PINKER: I think that there is a quasi-religious theory of human nature that is prevalent among pundits and intellectuals, which includes both empirical assumptions about how the mind works and a set of values that people hang on those assumptions. The theory is has three parts. One is the doctrine of "the blank slate": that we have no inherent talents or temperaments, because the mind is shaped completely by the environment—parenting, culture, and society. The second is "the noble savage": that evil motives are not inherent to people but come from corrupting social institutions.
These three idea ideas are increasingly being challenged by the sciences of the mind, brain, genes, and evolution, but they are held as much for their moral and political uplift as for any empirical rationale. People think that these doctrines are preferable on moral grounds and that the alternative is a forbidden territory that we should avoid at all costs. One of them is a simple logical point that no matter how important learning and culture and socialization are, they don't happen by magic.
There has to be innate circuitry that does the learning, that creates the culture, that acquires the culture, and that responds to socialization. Once you try to specify what those learning mechanisms are, you're forced to posit a great deal of innate structure to the mind. It's also been undermined by behavioral genetics, which has found that at least half of the variation in personality and intelligence in a society comes from differences in the genes. The most dramatic demonstration of this fact is that that identical twins who were separated at birth have fantastic similarities in their talents and tastes.
The Blank Slate has also undermined by evolutionary psychology and anthropology. For example, despite the undeniable variation among cultures, we now know that there is a vast set of universal traits that are common to all of the world's 6, cultures. Also, evolutionary psychology has shown that many of our motives make no sense in terms of our day-to-day efforts to enhance our physical and psychological well-being, but they can be explained in terms of the mechanism of natural selection operating in the environment in which we evolved.
A relatively uncontroversial example is our tastes for sugar and fat, which were adaptive in an environment in which those nutrients were in short supply but don't do anyone any good in a modern environment in which they are cheap and available anywhere. A more controversial example may be the universal thirst for revenge, which was one's only defense in a world in which one couldn't dial to get the police to show up if one's interests were threatened. A belligerent stance was one's only deterrent against other people whose interests were in conflict with one's own.
Another one is our taste for attractive marriage partners. As wise people have pointed out for millennia, this makes no sense in terms of how happy or compatible the couple will be. The curve of your date's nose, or the shape of her chin, doesn't predict how well one you're going to get along with her for the rest of your life. But evolutionary psychology has show that the physical features of beauty are cues to health and fertility.
Our fatal weakness for attractive partners can be explained in terms of our evolutionary history, not our personal calculations of well-being. The Blank Slate has also been undermined by brain science. The brain obviously has a great deal of what neuroscientists call plasticity—that's what allows us to learn. But the newest research is showing that many properties of the brain are genetically organized, and don't depend on information coming in from the senses.
The doctrine of the noble savage has been undermined by a revolution in our understanding of non-state societies.
- Human Culture, an Evolutionary Force.
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- Mutation, Not Natural Selection, Drives Evolution | pefawuqa.cf.
- NOTHING IN EVOLUTION MAKES SENSE EXCEPT IN LIGHT OF POPULATION GENETICS.
Many intellectuals believe that violence and war among hunter-gatherers is rare or ritualistic, and that the battle is called to a halt as soon as the first man falls. But studies that actually count the dead bodies have shown that the homicide rates among prehistoric peoples are orders of magnitude higher than the ones in modern societies—even taking into account the statistics from two world wars! We also have evidence that nasty traits such as psychopathy, violent tendencies, a lack of conscientiousness, and an antagonistic personality, are to a large extent heritable. And there are mechanisms in the brain, probably shared across primates, that underlie violence.
All these suggest that what we don't like about ourselves can't just be blamed on the institutions of a particular society. And the ghost in the machine has been undermined by cognitive science and neuroscience. The foundation of cognitive science is the computational theory of mind—the idea that intelligence can be explained as a kind of information-processing, and that motivation and emotion can be explained as feedback system.
Feats and phenomena that were formerly thought to rely on mental stuff alone, such as beliefs, desires, intelligence, and goal-directed behavior can be explained in physical terms. And neuroscience has most decisively exorcised the ghost in the machine by showing that our thoughts, feelings, urges, and consciousness depend completely on the physiological activity of the brain. The others are cognitive science, cognitive neuroscience and behavioral genetics. There's a sense in which all psychology is evolutionary. When it comes to understanding a complex psychological faculty such as thirst or shape perception or memory, psychologists have always appealed to their evolutionary functions, and it's never been particularly controversial.
It's no coincidence that the effects of thirst are to keep the amount of water and the electrolyte balance in the body within certain limits required for survival—without such a mechanism, organisms would plump up and split like a hot dog on a grill or shrivel up like a prune.
Likewise, it can't be a coincidence that the brain compares the images from the two eyeballs and uses that information to compute depth. Without such an ability we'd be more likely to bump into trees and fall off cliffs. The only explanation, other than creationism, is that those systems evolved because they allowed our ancestors to survive and reproduce better than the alternatives.
Evolutionary psychology is taking that mindset and applying it to more emotionally charged aspects of behavior, such as sexuality, violence, beauty, and family feelings. One reason that evolution is more controversial in these areas than it is in the study of thirst is that the implications of evolution are less intuitive in the case of emotions and social relations. You don't need to know much evolutionary biology to say that it's useful to have stereo vision or thirst. But when it comes to how organisms deal with one another, common sense is no substitute for good evolutionary theory.
We have no good intuitions about whether it's adaptive, in the narrow biologist's sense, to be monogamous or polygamous, to treat all your children equally or to play favorites, to be attracted to one kind of facial geometry or another. There you have to learn what the best evolutionary biology predicts. So evolutionary thinking in those fields is more surprising than in the rest of psychology.
PINKER: Both of them, to their great credit, have addressed what may be the most important puzzle in the history of psychology. It's one that most psychologists themselves don't appreciate, and that most intellectuals don't understand even when it's explained in Newsweek or the daily papers. Here's the puzzle. We know that genes matter in the formation of personalities.
Probably about half of the variation in personality can be attributed to differences in genes. People then conclude, well the other half must come from the way your parents brought you up: half heredity, half environment, a nice compromise. Concretely, here's what the behavioral geneticists have found.
Everyone knows about the identical twins separated at birth that have all of these remarkable similarities: they score similarly on personality tests, they have similar tests in music, similar political opinions, and so on. But the other discovery, which is just as important, though less well appreciated, is that the twins separated at birth are no more different than the twins who are brought up together in the same house with the same parents, the same number of TV sets in the house, same number of books, same number of guns, and so on.
Growing up together doesn't make you more similar in intelligence or in personality over the long run. A corroborating finding is that adopted siblings, who grow up in the same house but don't share genes, are not correlated at all. They are no more similar than two people plucked off the street at random.
So no, it's not all in the genes, but what isn't in the genes isn't in the family environment either. It can't be explained in terms of the overall personalities or the child-rearing practices of parents. Both Harris and Sulloway, and a handful of other psychologists like David Rowe, Robert Plomin, and Sandra Scarr, have called attention to this puzzle: what are the non-genetic determinants of personality and intelligence, given that they almost certainly are not the family environment. Many people, still groping for a way to put parents back into the picture, assume that differences among siblings must come from differences in the way parents treat their different children.
Forget it. The best studies have shown that when parents treat their kids differently, it's because the kids are different to begin with, just as anyone reacts differently to different people depending on their personalities. Any parent of more than one child knows that children are little people, born with personalities. Where these two differ is that Sulloway argues that the unexplained variation comes from the way that children differentiate themselves from their siblings in the family.
They take these strategies for competing for parental attention and resources outside the family and react to nonrelatives using the same strategies that worked for them inside the family. Harris argues that the missing variance comes from how children survive within peer groups—how they find a niche in their own society and develop strategies to prosper in it. I think that Sulloway has captured something about the dynamics among siblings within the family.
But I'm not convinced that these strategies shape their personalities outside the family. What works with your little brother is not necessarily going to work with strangers and friends and colleagues. And indeed most of the data that support Sulloway come from studies in which siblings rate their siblings or parents rate their children, or in which siblings rate themselves with respect to their siblings.
The theory is not well-supported by studies that look at the personality of people outside the home. Indeed, it's a major tenet of evolutionary psychology that one's relationships with kin are very different from ones relationships with non-relatives. As for Judy Harris, I am completely persuaded by her argument that socialization takes place in the peer group rather than in the family.
This is not a banal claim—most child psychologists won't go near it. But it survives one empirical test after another. To take a few examples: kids almost always end up with the accent of their peers, never their parents. Children of culturally inept immigrants do just fine if they can learn the ropes from native-born peers. Children who are thrown together without an adult language to model will invent a language of their own. And many studies have shown that radical variations in parenting practice, such as whether you grow up in an Ozzie and Harriet family or a hippie commune, whether you have two parents of the same sex or one of each, whether you spent your hours in the family home or a day care center, whether you are an only child or come from a large family, or whether you were conceived the normal way or in a laboratory dish, leave no lasting marks on your personality, as long as you are part of a standard peer group.
What Harris's theory has not explained to my satisfaction, at least not yet, is the missing variation in personality per se. Personality and socialization aren't the same thing. Socialization is how you become a functioning person in a society—speak the language, win friends, hold a job, wear the accepted kinds of clothing and so on. Personality is whether you're nice or nasty, bold or shy, conscientious or lackadaisical. Here's the problem. Let's to go back to our touchstone: identical twins brought up together, who share both their genes and their environment, but nonetheless are not identical in personality.
They almost certainly will have grown up in the same peer groups, or at least the same kinds of peer groups, and their personalities and physical characteristics will tend to place them in the same niches within those peer groups. So peer groups by themselves can't explain the unexplained variation in personality. To be fair, Harris points out that which niche you fill in a peer group—the peacemaker, the loose cannon, the jester, the facilitator, and so on—might partly be determined by chance: which niche is left open when you find a circle of buddies to hang out with.
I think there's something to that, but it's a special case of what might be an enormous role for chance in the shaping of who we are. In addition to which niche was open in your peer group, there are other unpredictable events that happened to each of as we grew up. Which twin got the top bunk bed, which got the bottom bunk bed?
Did you get chased by a dog, or dropped on your head, or infected by a virus, or smiled on by a teacher? And there are even more chance events in the wiring of the brain in utero and the first couple of years of life. We know that there isn't nearly enough information in the genome to specify the brain down to the last synapse, and that the brain isn't completely shaped by incoming sensory information either. Based on studies of the development of simple organisms like fruit flies and roundworms, we know that much in development is a matter of chance.
You can have genetically homogeneous strains of roundworm brought up in the same monotonous laboratory conditions, and find that one lives three times as long as the other. Or two fruitflies from inbred strains, which are in effect clones, can be physically different—they can have different numbers of bristles under each wing, for example. If in simple organisms like worms and flies can turn out differently for capricious and unpredictable reasons, then surely chance plays an even bigger role in the way our brains develop. Decades ago he argued that our capacity for language is an innate ability of the human mind, and he connected his theories to enlightenment philosophers and political thinkers who acknowledged the importance of human nature.
The year-old challenge to Darwin that is still making waves in research : Nature News & Comment
In graduate school my mentors were Steve Kosslyn, who trained me to be an experimental psychologist, and Roger Brown, who invented the modern science of language acquisition and got me interested in the topic. Roger was also a gifted writer, with a great wit and panache. He certainly inspired me to pay attention to clarity, style, and breadth in writing. Joan Bresnan, a brilliant linguist, was my postdoctoral adviser, and she sharpened my formal and computational and mathematical competence.
I have been interested in behavioral genetics ever since I read about the work of Tom Bouchard and David Lykken in Science in the late s, but it was Judy Harris who really forced me to think through the implications of that work, and of work in social and personality development more generally.
Also, many of the child psychologists who are still stuck on parents as the shapers of childrens' personality and intelligence. Third, the neural network modelers who have tried to revive the laws of association as an explanation for all aspects of language and cognition. Fourth, some of the more extreme enthusiasts of neural plasticity, who believe that the brain is infinitely malleable, and that this holds great promise for education and child-rearing and successful aging. Fifth, people with sympathies for the romantic revolutionary politics of the 60s and 70s, which is where the initial opposition to sociobiology came from.
They have always been enraged by the claim that limitations on human nature might constrain our social arrangements. One example is architecture and urban planning. The 20th century saw the rise of a movement that has been called "authoritarian high modernism," which was contemporaneous with the ascendance of the blank slate. City planners believed that people's taste for green space, for ornament, for people-watching, for cozy places for intimate social gatherings, were just social constructions. They were archaic historical artifacts that were getting in the way of the orderly design of cities, and should be ignored by planners designing optimal cities according to so-called scientific principles.
Le Corbusier was the clearest example. He and other planners had a minimalist conception of human nature. A human being needs so many cubic of air per day, a temperature within a certain range, so many gallons of water, and so many square feet in which to sleep and work. Houses became "machines for living," and cities were designed around the most efficient way to satisfy this short list of needs, namely freeways, huge rectangular concrete housing projects, and open plazas.
In extreme cases this led to the wastelands of planned cities like Brasilia; in milder cases it gave us the so-called urban renewal projects in American cities and the dreary highrises in the Soviet Union and English council flats. Ornamentation, human scale, green space, gardens, and comfortable social meeting places were written out of the cities because the planners had a theory of human nature that omitted human esthetic and social needs. Another example is the arts.
In the 20th century, modernism and post-modernism took over, and their practitioners disdained beauty as bourgeois, saccharine, and lightweight. Art was deliberately made incomprehensible or ugly or shocking—again, on the assumption that people's tastes for attractive faces, landscapes, colors, and so on were reversible social constructions. This also led to an exaggeration of the dynamic of social status that has always been part of the arts.
The elite arts used to be aligned with the economic and political aristocracy. They involved displays of sumptuosity and the flaunting of rare and precious skills that only the idle rich could cultivate. But now that any now that any schmo can afford a Mozart CD or can go to a free museum, artists had to figure out new ways to differentiate themselves from the rabble. And so art became baffling and uninterpretable without acquaintance with arcane theory.
By their own admission, the humanities programs in universities, and institutions that promote new works of elite art, are in crisis. People are staying away in droves. I don't think it takes an Einstein to figure out why. By denying people's sense of visual beauty in painting and sculpture, melody in music, meter and rhyme in poetry, plot and narrative and character in fiction, the elite arts wrote off the vast majority of their audience—the people who approach art in part for pleasure and edification rather than social one-upmanship.
Today there are movements in the arts to reintroduce beauty and narrative and melody and other basic human pleasures. And they are considered radical extremists! EDGE: Why do people still treat art and literary critics as the wisest and most relevant intellectuals? In terms of literature, why is it that in the leading cultural magazines, you can still find a lot more of Virginia Woolf, Lytton Strachey, and Bloomsbury, than discussions about the issues you and other scientists are raising?
Many studies show that that people hallucinate moral virtue in other people who are high in status—people who are good-looking, or powerful, or well-connected, or artistically or athletically talented.
Status and virtue are cross-wired in the human brain. We see it in language, where words like "noble" and "ugly" have two meanings. The deification of Princess Diana and John F. Kennedy Jr. I think this confusion leads intellectuals and artists themselves to believe that the elite arts and humanities are a kind of higher, exalted form of human endeavor. Anyone else having some claim to insights into the human condition is seen as a philistine, and possibly as immoral if they are seen as debunking the pretensions of those in the arts and the humanities. To be fair, there are other strands of the arts and humanities, sometimes brushed aside in the 20th century, that resonate quite well with the arguments that I've been making.
Many artists and scholars have pointed out that ultimately art depends on human nature. The aesthetic and emotional reactions that we have to works of art depend on how our brain is put together. Art works because it appeals to certain faculties of the mind. Music depends on details of the auditory system, painting and sculpture on the visual system.
Poetry and literature depend on language. In the two hours that elapsed before my ague fit was over I had thought out almost the whole of the theory, and the same evening I sketched the draft of my paper, and in the two succeeding evenings wrote it out in full, and sent it by the next post to Mr. Up to this time the only letters I had received from him were those printed in the second volume of his Life and Letters, vol.
The immediate result of my paper was that Darwin was induced at once to prepare for publication his book on the Origin of Species in the condensed form in which it appeared, instead of waiting an indefinite number of years to complete a work on a much larger scale which he had partly written, but which in all probability would not have carried conviction to so many persons in so short a time. I feel much satisfaction in having thus aided in bringing about the publication of this celebrated book, and with the ample recognition by Darwin himself of my independent discovery of "natural selection.
Instability of Varieties supposed to prove the permanent distinctness of Species. ONE of the strongest arguments which have been adduced to prove the original and permanent distinctness of species is, that varieties produced in a state of domesticity are more or less unstable, and often have a tendency, if left to themselves, to return to the normal form of the parent species; and this instability is considered to be a distinctive peculiarity of all varieties, even of those occurring among wild animals in a state of nature, and it constitute a provision for preserving unchanged the originally created distinct species.
In the absence or scarcity of facts and observations as to varieties occurring among wild animals, this argument has had great weight with naturalists, and has led to a very general and somewhat prejudiced belief in the stability of species. Equally general, however, is the belief in what are called "permanent or true varieties,"—races of animals which continually propagate their like, but which differ so slightly although constantly from some other race, that the one is considered to be a variety of the other.
Which is the variety and which the original species, there is generally no means of determining, except in those rare cases in which the one race has been known to produce an offspring unlike itself and resembling the other. This, however, would seem quite incompatible with the "permanent invariability of species,". It will be observed that this argument rests entirely on the assumption that varieties occurring in a state of nature are in all respects analogous to or even identical with those of domestic animals, and are governed by the same laws as regards their permanence or further variation.
But it is the object of the present paper to show that this assumption is altogether false, that there is a general principle in nature which will cause many varieties to survive the parent species, and to give rise to successive variations departing further and further from the original type, and which also produces, in domesticated animals, the tendency of varieties to return to the parent form. The life of wild animals is a struggle for existence. The full exertion of all their faculties and all their energies is required to preserve their own existence and provide for that of their infant offspring.
The possibility of procuring food during the least favourable seasons, and of escaping the attacks of their most dangerous enemies, are the primary conditions which determine the existence both of individuals and of entire species. These conditions will also determine the population of a species; and by a careful consideration of all the circumstances we may be enabled to comprehend, and in some degree to explain, what at first sight appears so inexplicable—the excessive abundance of some species, while others closely allied to them are very rare.
The general proportion that must obtain between certain groups of animals is readily seen. Large animals cannot be so abundant as small ones; the carnivora must be less numerous than the herbivora; eagles and lions can never be so plentiful as pigeons and antelopes; and the wild asses of the Tartarian deserts cannot equal in numbers the horses of. The greater or less fecundity of an animal is often considered to be one of the chief causes of its abundance or scarcity; but a consideration of the facts will show us that it really has little or nothing to do with the matter.
Even the least prolific of animals would increase rapidly if unchecked, whereas it is evident that the animal population of the globe must be stationary, or perhaps, through the influence of man, decreasing. Fluctuations there may be; but permanent increase, except in restricted localities, is almost impossible. For example, our own observation must convince us that birds do not go on increasing every year in a geometrical ratio, as they would do were there not some powerful check to their natural increase. Very few birds produce less than two young ones each year, while many have six, eight, or ten; four will certainly be below the average; and if we suppose that each pair produce young only four times in their life, that will also be below the average, supposing them not to die either by violence or want of food.
Yet at this rate how tremendous would be the increase in a few years from a single pair! A simple calculation will show that in fifteen years each pair of birds would have increased to nearly ten millions! With such powers of increase the population must have reached its limits, and have become stationary, in a very few years after the origin of each species.
It is evident, therefore, that each year an immense number of birds must perish—as many in fact as are born; and as on the lowest calculation the progeny are each year twice as numerous as their parents, it follows that, whatever be the average number of individuals existing in any given country, twice that number must perish annually, —a striking result, but one which seems at least highly probable, and is perhaps under rather than over the truth.
It would therefore appear that, so far as the continuance of the species and the keeping up the average number of individuals are concerned, large broods are superfluous. On the average all above one become. The number would really amount to more than two thousand millions! This is strikingly proved by the case of particular species; for we find that their abundance in individuals bears no relation whatever to their fertility in producing offspring.
Perhaps the most remarkable instance of an immense bird population is that of the passenger pigeon of the United States, which lays only one, or at most two eggs, and is said to rear generally but one young one. Why is this bird so extraordinarily abundant, while others producing two or three times as many young are much less plentiful?
The explanation is not difficult. The food most congenial to this species, and on which it thrives best, is abundantly distributed over a very extensive region, offering such differences of soil and climate, that in one part or another of the area the supply never fails. The bird is capable of a very rapid and long-continued flight, so that it can pass without fatigue over the whole of the district it inhabits, and as soon as the supply of food begins to fail in one place is able to discover a fresh feeding-ground.
This example strikingly shows us that the procuring a constant supply of wholesome food is almost the sole condition requisite for ensuring the rapid increase of a given species, since neither the limited fecundity nor the unrestrained attacks of birds of prey and of man are here sufficient to check it. In no other birds are these peculiar circumstances so strikingly combined. Either their food is more liable to failure, or they have not sufficient power of wing to search for it over an extensive area, or during some season of the year it becomes very scarce, and less wholesome substitutes have to be found; and thus, though more fertile in offspring, they can never increase beyond the supply of food in the least favourable seasons.
In the Light of Evolution: Volume I: Adaptation and Complex Design.
Many birds can only exist by migrating, when their food becomes scarce, to regions possessing a milder, or at least a different climate, though, as these migrating birds are seldom excessively abundant, it is evident that the countries they visit are still deficient in a constant and abundant supply of wholesome food. Those whose organisation does not permit them to migrate when their food becomes periodically scarce, can never attain a large population.
This is probably the. Thus the house sparrow is more abundant than the redbreast, because its food is more constant and plentiful,—seeds of grasses being preserved during the winter, and our farm-yards and stubble-fields furnishing an almost inexhaustible supply. Why, as a general rule, are aquatic, and especially sea-birds, very numerous in individuals? Not because they are more prolific than others, generally the contrary; but because their food never fails, the sea-shores and river-banks daily swarming with a fresh supply of small mollusca an crustacea. Exactly the same laws will apply to mammals.
Wild cats are prolific and have few enemies; why then are they never as abundant as rabbits? The only intelligible answer is, that their supply of food is more precarious. It appears evident, therefore, that so long as a country remains physically unchanged, the numbers of its animal population cannot materially increase. If one species does so, some others requiring the same king of food must diminish in proportion. The numbers that die annually must be immense; and as the individual existence of each animal depends upon itself, those that die must be the weakest—the very young, the aged, and the diseased—while those that prolong their existence can only be the most perfect in health and vigour—those who are best able to obtain food regularly, and avoid their numerous enemies.
It is, as we commenced by remarking, "a struggle for existence," in which the weakest and least perfectly organized must always succumb. The Abundance or Rarity of a Species dependent upon its more or less perfect Adaptation to the Conditions of Existence. It seems evident that what takes place among the individuals of a species must also occur among the several allied species of a group,—viz. Between these extremes the species will present various degrees of capacity for ensuring the means of preserving life; and it is thus we account for the abundance or rarity of species.
Our ignorance will generally prevent us from accurately tracing the effects to their causes; but could we become perfectly acquainted with the organisation and habits of the various species of animals, and could we measure the capacity of each for performing the different acts necessary to its safety and existence under all the varying circumstances by which it is surrounded, we might be able even to calculate the proportionate abundance of individuals which is the necessary result. If now we have succeeded in establishing these two points—1st, that the animal population of a country is generally stationary, being kept down by a periodical deficiency of food, and other checks; and, 2d, that the comparative abundance or scarcity of the individuals of the several species is entirely due to their organisation and resulting habits, which, rendering it more difficult to procure a regular supply of food and to provide for their personal safety 1 in some cases than in others, can only be balanced by a difference in the population which have to exist in a given area —we shall be in a condition to proceed to the consideration of varieties, to which the preceding remarks have a direct and very important application.
Useful Variations will tend to Increase; useless or hurtful Variations to Diminish. Most or perhaps all the variations from the typical form of a species must have some definite effect, however slight, on the habits or capacities of the individuals. Even a change of colour might, by rendering them more or less distinguishable, affect their safety; a greater or less development of hair might modify their habits.
More important changes, such as an increase in the power or dimensions of the limbs or any of the external organs, would more or less affect their mode of procuring food or the range of country which they could in-. But it must be remembered that the writer had no opportunity of correcting the proofs of this paper. It is also evident that most changes would affect, either favourably or adversely, the powers of prolonging existence. An antelope with shorter or weaker legs must necessarily suffer more from the attacks of the feline carnivora; the passenger pigeon with less powerful wings would sooner or later be affected in its powers of procuring a regular supply of food; and in both cases the result must necessarily be a diminution of the population of the modified species.
If on the other hand, any species should produce a variety having slightly increased powers of preserving existence, that variety must inevitably in time acquire a superiority in numbers. These results must follow as surely as old age, intemperance, or scarcity of food produce an increased mortality. In both cases there may be many individual exceptions: but on the average the rule will invariably be found to hold good.
- Science in History: Volume 1: The Emergence of Science.
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- They Were You?
- Playing Dead.
All varieties will therefore fall into two classes—those which under the same conditions would never reach the population of the parent species, and those which would in time obtain and keep a numerical superiority. Now, let some alteration of physical conditions occur in the district—a long period of drought, a destruction of vegetation by locusts, the irruption of some fresh carnivorous animal seeking "pastures new"— any change in fact tending to render existence more difficult to the species in question, and tasking its utmost powers to avoid complete extermination,—it is evident that, of all the individuals composing the species, those forming the least numerous and most feebly organised variety would suffer first, and, were the pressure severe, must soon become extinct.
The same causes continuing in action, the parent species would next suffer, would gradually diminish in numbers, and with a recurrence of similar unfavourable conditions might also become extinct. The superior variety would then alone remain, and on a return to favourable circumstances would rapidly increase in numbers and occupy the place of the extinct species and variety.
The variety would now have replaced the Species, of it would be a more perfectly developed and more organised form. It would be in all respects better a. Such a variety could not return to the original form; for that form is an inferior one, and could never compete with it for existence. Granted, therefore, a "tendency" to reproduce the original type of the species, still the variety must ever remain preponderant in numbers, and under adverse physical conditions again alone survive.
But this new, improved, and populous race might itself, in course of time, give rise to new varieties, exhibiting several diverging modifications of forms, any of which, tending to increase the facilities for preserving existence, must, by the same general law, in their turn become predominant. Here, then, we have progression and continued divergence deduced from the general laws which regulate the existence of animals in a state of nature, and from the undisputed fact that varieties do frequently occur.
It is not, however, contended that this result would be invariable; a change of physical conditions in the district might at times materially modify it, rendering the race which had been the most capable of supporting existence under the former conditions now the least so, and even causing the extinction of the newer and, for a time, superior race, while the old or parent species and its first inferior varieties continued to flourish. Variations in unimportant parts might also occur, having no perceptible effect on the life-preserving powers; and the varieties so furnished might run a course parallel with the parent species, either giving rise to further variations or returning to the former type.
All we argue for is, that certain varieties have a tendency to maintain their existence longer than the original species, and this tendency, must itself felt; for though the doctrine of chances or averages can never be trusted on a limited scale, yet, if applied to high numbers, the results come nearer to what theory demands, and, as we approach to an infinity of examples, become strictly accurate. Now the scale on which nature works is so vast—the numbers of individuals and the periods of time with which she deals approach so near to infinity—that any cause, however slight, and however liable to be veiled and counteracted by accidental circumstances, must in the end produce its full legitimate results.
Let us now turn to domesticated animals, and inquire how varieties produced among them are affected by the principles here enunciated. The essential difference in the condition of wild and domestic animals is this,—that among the former, their well-being and very existence depend upon the full exercise and healthy condition of all their senses and physical powers, whereas, among the latter, these are only partially exercised, and in some cases are absolutely unused.
A wild animal has to search, and often to labour, for every mouthful of food—to exercise sight, hearing, and smell in seeking it, and in avoiding dangers, in procuring shelter from the inclemency of the seasons, and in providing for the subsistence and safety of its offspring. There is no muscle of its body that is not called into daily and hourly activity; there is no sense or faculty that is not strengthened by continual exercise. The domestic animal, on the other hand, has food provided for it, is sheltered, and often confined, to guard it against the vicissitudes of the seasons, is carefully secured from the attacks of its natural enemies, and seldom even rears its young without human assistance.
Half of its senses and faculties become quite useless, and the other half are but occasionally called into feeble exercise, while even its muscular system is only irregularly brought into action. Now when a variety of such an animal occurs having increased power or capacity in any organ or sense, such increase is totally useless, is never called into action, and may even exist without the animal ever becoming aware of it.
In the wild animal, on the contrary, all its faculties and powers being brought into full action for the necessities of existence, any increase becomes immediately available, is strengthened by exercise, and must even slightly modify the food, the habits, and the whole economy of the race. It creates as it were a new animal, one of superior powers, and which will necessarily increase in numbers and outlive those which are inferior to it. Again, in the domesticated animal all variations have an equal chance of continuance; and those which would decidedly render a wild animal unable to compete with its fellows and continue its existence are no disadvantage what-.
Our quickly fattening pigs, short-legged sheep, pouter pigeons, and poodle dogs could never have come into existence in a state of nature, because the very first steps towards such inferior forms would have led to the rapid extinction of the race; still less could they now exist in competition with their wild allies. The great speed but slight endurance of the racehorse, the unwieldly strength of the ploughman's team, would both be useless in a state of nature.
If turned wild on the pampas, such animals would probably soon become extinct, or under favourable circumstances might each gradually lose those extreme qualities which would never be called into action, and in a few generations revert to a common type, which must be that in which the various powers and faculties are so proportioned to each other as to be best adapted to procure food and secure safety,—that in which, by the full exercise of every part of its organisation, the animal can alone continue to live. Domestic varieties, when turned wild, must return to something near the type of the original wild stock, or become altogether extinct.
We see, then, that no inferences as to the permanence of varieties in a state of nature can be deduced from the observations of those occurring among domestic animals. The two are so much opposed to each other in every circumstance of their existence, that what applies to the one is almost sure not to apply to the other. Domestic animals are abnormal, irregular, artificial; they are subject to variations which never occur, in a state of nature: their very existence depends altogether on human care—so far are many of them removed from that just proportion of faculties, that true balance of organisation, by means of which alone an animal left to its own resources can preserve its existence and continue its race.
The hypothesis of Lamarck—that progressive changes in species have been produced by the attempts of animals to. Those individuals which do not vary sufficiently will perish. The powerful retractile talons of the falcon and the cat tribes have not been produced or increased by the volition of those animals; but among the different varieties which occurred in the earlier and less highly organised forms of these groups, those always survived longest which had the greatest facilities for seizing their prey.
Neither did the giraffe acquire its long neck by desiring to reach the foliage of the more lofty shrubs, and constantly stretching its neck for the purpose, but because any varieties which occurred among its antitypes with a longer neck than usual at once secured a fresh range of pasture over the same ground as their shorter-necked companions, and on the first scarcity of food were thereby enabled to outlive them.
Even the peculiar colours of many animals, more especially of insects, so closely resembling the soil or leaves or bark on which they habitually reside, are explained on the same principle; for though in the course of ages varieties of many tints may have occurred, yet those races having colours best adapted to concealment from their enemies would inevitably survive the longest.
We have also here an acting cause to account for that balance so often observed in nature,—a deficiency in one set of organs always being compensated by an increased development of some others—powerful wings accompanying weak feet, or great velocity making up for the absence of defensive weapons; for it has been shown that all varieties in which an unbalanced deficiency occurred could not long continue their existence.
The action of this principle is exactly like that of the centrifugal governor of the steam-engine, which checks and corrects any irregularities almost before they become evident; and in like manner no unbalanced deficiency in the animal kingdom can ever reach any conspicuous magnitude, because it would make itself felt at the very first step, by. An origin such as is here advocated will also agree with the peculiar character of the modifications of form and structure which obtain in organised beings—the many lines of divergence from a central type, the increasing efficiency and power of a particular organ through a succession of allied species, and the remarkable persistence of unimportant parts, such as colour, texture of plumage and hair, form of horns or crests, through a series of species differing considerably in more essential characters.
It also furnishes us with a reason for that "more specialised structure" which Professor Owen states to be a characteristic of recent compared with extinct forms, and which would evidently be the result of the progressive modification of any organ applied to a special purpose in the animal economy. We believe we have now shown that there is an tendency in nature to the continued progression of certain classes of varieties further and further from the original type—a progression to which there appears no reason to assign any definite limits—and that the same principle which produces this result in a state of nature will also explain why domestic varieties have a tendency, when they become wild, to revert to the original type.
This progression, by minute steps, in various directions, but always checked and balanced by the necessary conditions, subject to which alone existence can be preserved, may, it is believed, be followed out so as to agree with all the phenomena presented by organised beings, their extinction and succession in past ages, and all the extraordinary modifications of form, instinct, and habits which they exhibit. THERE is no more convincing proof of the truth of a comprehensive theory than its power of absorbing and finding a place for new facts, and its capability of interpreting phenomena which had been previously looked upon as unaccountable anomalies.
It is thus that the law of universal gravitation and the undulatory theory of light have become established and universally accepted by men of science. Fact after fact has been brought forward as being apparently inconsistent with them, and one after another these very facts have been shown to be the consequences of the laws they were at first supposed to disprove. A false theory will never stand this test. Advancing knowledge brings to light whole groups of facts which it cannot deal with, and its advocates steadily decrease in numbers, notwithstanding the ability and scientific skill with which it may have been supported.
The great name of Edward Forbes did not prevent his theory of "Polarity in the distribution of Organic beings in Time" from dying a natural death; but the most striking illustration of the behaviour of a false theory is to be found in the "Circular and Quinarian System" of classification propounded by MacLeay, and developed by Swainson, with an amount of knowledge and ingenuity that has rarely been surpassed. This theory was eminently attractive, both from its symmetry and completeness, and from the interesting nature of the varied analogies and affinities.
Swainson developed it in most departments of the animal kingdom, made it widely known; and in fact for a long time these were the best and almost the only popular text-books for the rising generation of naturalists. It was favourably received too by the older school, which was perhaps rather an indication of its unsoundness. A considerable number of well-known naturalists either spoke approvingly of it, or advocated similar principles, and for a good many years it was decidedly in the ascendant.
With such a favourable introduction, and with such talented exponents, it must have become established if it had had any germ of truth in it; yet it quite died out in a few short years; its very existence is now a matter of history; and so rapid was its fall that its talented creator, Swainson, perhaps lived to be the last man who believed in it.
Such is the course of a false theory. That of a true one is very different, as may be well seen by the progress of opinion on the subject of Natural Selection. In less than eight years The Origin of Species has produced conviction in the minds of a majority of the most eminent living men of science. New facts, new problems, new difficulties as they arise are accepted, solved, or removed by this theory; and its principles are illustrated by the progress and conclusions of every well established branch of human knowledge.
It is the object of the present chapter to show how it has recently been applied to connect together and explain a variety of curious facts which had long been considered as inexplicable anomalies. Perhaps no principle has ever been announced so fertile in results as that which Mr. Darwin so earnestly impresses upon us, and which is indeed a necessary deduction from the theory of Natural Selection, namely—that none of the definite facts or organic nature, no special organ, no characteristic form of marking, no peculiarities of instinct or of habit, no relations between species or between groups of species—can exist, but which must now be or once have been useful to the individuals or the races which possess them.
The adaptation of the external colouring of animals to their conditions of life has long been recognised, and had been imputed either to an originally created specific peculiarity, or to the direct action of climate, soil, or food. Where the former explanation has been accepted it has completely checked inquiry, since we could never get any further than the fact of the adaptation.
There was nothing more to be known about the matter. The second explanation was soon found to be quite inadequate to deal with all the varied phases of the phenomena, and to be contradicted by many well known facts. For example, wild rabbits are always of gray of brown tints well suited for concealment among grass and fern. But when these rabbits are domesticated, without any change of climate or food, they vary into white or black, and these varieties may be multiplied to any extent, forming white or black races.
Exactly the same thing has occurred with pigeons; and in the case of rats and mice, the white variety has not been shown to be at all dependent on alteration of climate, food, or other external conditions. In many cases the wings of an insect not only assume the exact tint of the bark or leaf it is accustomed to rest on, but the form and veining of the leaf or the exact rugosity of the bark is imitated; and these detailed modifications cannot be reasonably imputed to climate or to food, since in many cases the species does not feed on the substance it resembles, and when it does, no reasonable connection can be shown to exist between the supposed causes and the effect produced.
It was reserved for the theory of Natural Selection to solve all these problems, and many others which were not at first supposed to be directly connected with them. To make these latter intelligible, it will be necessary to give a sketch of the whole series of phenomena which may be classed under the head of useful or protective resemblances.
Concealment, more or less complete, is useful to many animals, and absolutely essential to some. Those which have numerous enemies from which they cannot escape by rapidity of motion find safety in concealment. Those which prey upon others must also be so constituted as not to alarm them by their presence or their approach, or they would soon die of hunger.
Now it is remarkable in how many cases nature gives this boon to the animal, by colouring it with such tints as may best serve to enable it to escape from its enemies or to entrap its prey. Desert animals as a rule are desert- coloured. The lion is a typical example of this, and must be almost invisible when crouched upon the sand or among desert rocks and stones.
Antelopes are all more or less sandy-coloured. The camel is pre-eminently so. The Egyptian cat and the Pampas cat are sandy are earth-coloured. The Australian kangaroos are of the same tints, and the original colour of the wild horse is supposed to have been a sandy or clay-colour. The desert birds are still more remarkably protected by their assimilative hues. The stonechats, the larks, the quails, the goatsuckers and the grouse, which abound in the North African and Asiatic deserts, are all tinted and mottled so as to resemble with wonderful accuracy the average colour and aspect of the soil in the district they inhabit.
The Rev. Tristram, in his account of the ornithology of North Africa in the first volume of the Ibis, says: "In the desert, where neither trees, brushwood, nor even undulation of the surface afford the slightest protection to its foes, a modification of colour which shall be assimilated to that of the surrounding country is absolutely necessary. Hence without exception the upper plumage of every bird, whether lark, sylvain, or sand-grouse, and also the fur of all the smaller mammals, and the skin of all the snakes and lizards, is of one uniform isabelline or sand colour.
Almost equally striking are the cases of arctic animals possessing the white colour that best conceals them upon. The polar bear is the only bear that is white, and it lives constantly among snow and ice. The arctic fox, the ermine, and the alpine hare change to white in winter only, because in summer white would be more conspicuous than any other colour, and therefore a danger rather than a protection; but the American polar hare, inhabiting regions of almost perpetual snow, is white all the year round.
Other animals inhabiting the same Northern regions do not, however, change colour. The sable is a good example, for throughout the severity of a Siberian winter it retains its rich brown fur. But its habits are such that it does not need the protection of colour, for it is said to be able to subsist on fruits and berries in winter, and to be so active upon the trees as to catch small birds among the branches.
So also the woodchuck of Canada has a dark-brown fur; but then it lives in burrows and frequents river banks, catching fish and small animals that live in or near the water. Among birds, the ptarmigan is a fine example of protective colouring. Its summer plumage so exactly harmonises with the lichen-coloured stones among which it delights to sit, that a person may walk through a flock of them without seeing a single bird; while in winter its white plumage is an almost equal protection.
The snow-bunting, the jer-falcon, and the snowy owl are also white-coloured birds inhabiting the arctic regions, and there can be little doubt but that their colouring is to some extent protective. Nocturnal animals supply us with equally good illustrations. Mice, rats, bats and moles possess the least conspicuous of hues, and must be quite invisible at times when any light colour would be instantly seen.
Owls and goatsuckers are of those dark mottled tints that will assimilate with bark and lichen, and thus protect them during the day, and at the same time be inconspicuous in the dusk. It is only in the tropics, among forests which never lose their foliage, that we find whole groups of birds whose chief colour is green.
The parrots are the most striking example, but we have also a group of green pigeons in the East; and the barbets, leaf-thrushes, bee-eaters, white-eyes, turacos, and several smaller groups, have so much green in their plumage as to tend greatly to conceal them among the foliage.
The conformity of tint which has been so far shown to exist between animals and their habitations is of a somewhat general character; we will now consider the cases of more special adaptation. If the lion is enabled by his sandy colour readily to conceal himself by merely crouching down upon the desert, how, it may be asked, do the elegant markings of the tiger, the jaguar, and the other large cats, agree with this theory? We reply that these are generally cases of more or less special adaptation.
The tiger is a jungle animal, and hides himself among tufts of grass or of bamboos, and in these positions the vertical stripes with which his body is adorned must so assimilate with the vertical stems of the bamboo as to assist greatly in concealing him from his approaching prey. Among birds, the ptarmigan, already mentioned, must be considered a remarkable case of special adaptation. Another is a South American goatsucker Caprimulgus rupestris , which rests in the bright sunshine on little bare rocky islets in the Upper Rio Negro, where its unusually light colours so closely resemble those of the rock and sand that it can scarcely be detected till trodden upon.
The Duke of Argyll, in his Reign of Law, has pointed out the admirable adaptation of the colours of the woodcock to its protection. The various browns and yellows and pale ash-colour that occur in fallen leaves are all reproduced in its plumage, so that when, according to its habit, it rests upon the ground under trees, it is almost impossible to detect it.
In snipes the colours are modified so as to be equally in harmony with the prevalent forms and colours of marshy vegetation. Lester, in a paper read before the. See Darwinism, p. Rugby School Natural History Society, observes: "The wood-dove, when perched amongst the branches of its favourite fir, is scarcely discernible; whereas, were it among some lighter foliage, the blue and purple tints in its plumage would far sooner betray it. The robin redbreast too, although it might be thought that the red on its breast made it much easier to be seen, is in reality not at all endangered by it, Since it generally contrives to get among some russet or yellow fading leaves, where the red matches very well with the autumn tints, and the brown of the rest of the body with the bare branches.
Reptiles offer us many similar examples. The most arboreal lizards, the iguanas, are as green as the leaves they feed upon, and the slender whip-snakes are rendered almost invisible as they glide among the foliage by a similar coloration. How difficult it is sometimes to catch sight of the little green tree-frogs sitting on the leaves of a small plant enclosed in a glass case in the Zoological Gardens; yet how much better concealed must they be among the fresh green damp foliage of a marshy forest.
There is a North American frog found on lichen-covered rocks and walls, which is so coloured as exactly to resemble them, and as long as it remains quiet would certainly escape detection. Some of the geckos which cling motionless on the trunks of trees in the tropics are of such curiously marbled colours as to match exactly with the bark they rest upon. In every part of the tropics there are tree-snakes that twist among boughs and shrubs, or lie coiled up on the dense masses of foliage.
These are of many distinct groups, and comprise both venomous and harmless genera; but almost all of them are of a beautiful green colour, sometimes more or less adorned with white or dusky bands and spots. There can be little doubt that this colour is doubly useful to them, since it will tend to conceal them from their enemies, and will lead their prey to approach then unconscious of danger. Gunther informs me that there is only one genus of true arboreal snakes Dipsas whose colours are rarely green, but are of various shades of black, brown, and olive, and these are all nocturnal reptiles, and there can be little doubt conceal themselves during the day in holes, so that the green.
Fishes present similar instances. Many flat fish, as for example the flounder and the skate, are exactly the colour of the gravel or sand on which they habitually rest.
Among the marine flower gardens of an Eastern coral reef the fishes present every variety of gorgeous colour, while the river fish even of the tropics rarely if ever have gay or conspicuous markings. A very curious case of this kind of adaptation occurs in the sea-horses Hippocampus of Australia, some of which bear long foliaceous appendages resembling seaweed, and are of a brilliant red colour; and they are known to live among seaweed of the same hue, so that when at rest they must be quite invisible.
It is, however, in the insect world that this principle of the adaptation of animals to their environment is most fully and strikingly developed. In order to understand how general this is, it is necessary to enter somewhat into details, as we shall thereby be better able to appreciate the significance of the still more remarkable phenomena we shall presently have to discuss. It seems to be in proportion to their sluggish motions or the absence of other means of defence, that insects possess the protective colouring.
In the tropics there are thousands of species of insects which rest during the day clinging to the bark of dead or fallen trees; and the greater portion of these are delicately mottled with gray and brown tints, which, though symmetrically disposed and infinitely varied, yet blend so completely with the usual colours of the bark, that at two or three feet distance they are quite undistinguishable.
In some cases a species is known to frequent only one species of tree. This is the case with the common South American long-horned beetle Onychocerus scorpio , which, Mr. It is very abundant, but so exactly does it resemble the bark in colour and rugosity, and so closely does it cling. An allied species O. Both these insects are abundant, and we may fairly conclude that the protection they derive from this strange concealment is at least one of the causes that enable the race to flourish. Many of the species of Cicindela, or tiger beetle, will illustrate this mode of protection.
Our common Cicindela campestris frequents grassy banks, and is of a beautiful green colour, while C. A great number of the species found by myself in the Malay islands are similarly protected. The beautiful Cicindela gloriosa, of a very deep velvety green colour, was only taken upon wet mossy stones in the bed of a mountain stream, where it was with the greatest difficulty detected. A large brown species C. Where the sandy beach was coralline and nearly white, I found a very pale Cicindela; wherever it was volcanic and black, a dark species of the same genus was sure to be met with.
Kirby and Spence mention the small beetle Onthophilus sulcatus as being like the seed of an umbelliferous plant; and another, a small weevil, which is much persecuted by predatory beetles of the genus Harpalus, is of the exact colour of loamy soil, and was found to be particularly abundant in loam pits. A number of our small brown and speckled weevils at the approach of any object roll off the leaf they are sitting on, at. The distribution of colour in butterflies and moths respectively is very instructive from this point of view. The former have all their brilliant colouring on the upper surface of all four wings, while the under surface is almost always soberly coloured, and often very dark and obscure.
The moths on the contrary have generally their chief colour on the hind wings only, the upper wings being of dull, somber, and often imitative tints, and these generally conceal the hind wings when the insects are in repose. This arrangement of the colours is therefore eminently protective, because the butterfly always rests with his wings raised so as to conceal the dangerous brilliancy of his upper surface.
It is probable that if we watched their habits sufficiently we should find the under surface of the wings of butterflies very frequently imitative and protective. Wood has pointed out that the little orange-tip butterfly often rests in the evening on the green and white flower heads of an umbelliferous plant, the wild chervil, 1 and that when observed in this position the beautiful green and white mottling of the under surface completely assimilates with the flower heads and renders the creature very difficult to be seen.
It is probable that the rich dark colouring of the under side of our peacock, tortoiseshell, and red-admiral butterflies answers a similar purpose. Two curious South American butterflies that always settle on the trunks of trees Gynecia dirce and Callizona acesta have the under surface curiously striped and mottled, and when viewed obliquely must closely assimilate with the appearance of the furrowed bark of many kinds of trees. But the most wonderful and undoubted case of protective resemblance in a butterfly which I have ever seen, is that of the common Indian Kallima inachis, and its Malayan ally, Kallima paralekta.
The upper surface of these insects is very striking and showy, as they are of a large size, and are adorned with a broad band. The under side is very variable in colour, so that out of fifty specimens no two can be found exactly alike, but every one of them will be of some shade of ash or brown or ochre, such as are found among dead, dry, or decaying leaves.
The apex of the upper wings is produced into an acute point, a very common form in the leaves of tropical shrubs and trees, and the lower wings are also produced into a short narrow tail. Between these two points runs a dark curved line exactly representing the midrib of a leaf, and from this radiate on each side a few oblique lines, which serve to indicate the lateral veins of a leaf. We come now to a still more extraordinary part of the imitation, for we find representations of leaves in every stage of decay, variously blotched and mildewed and pierced with holes, and in many cases irregularly covered with powdery blackdots gathered into patches and spots, so closely resembling the various kinds of minute fungi that grow on dead leaves that it is impossible to avoid thinking at first sight that the butterflies themselves have been attacked by real fungi.
But this resemblance, close as it is, would be of little use if the habits of the insect did not accord with it. We might be sure, however, from the analogy of many other cases, that the habits of the insect are such as still further to aid its deceptive garb; but we are not obliged to make any such supposition, since I myself had the good fortune to observe scores of Kallima paralekta, in Sumatra, and to capture many of them, and can vouch for the accuracy of the following details.
These butterflies frequent dry forests and fly very swiftly. They were never seen to settle on a flower or a green leaf; but were many times lost sight of in a bush or tree of dead leaves. On such occasions. On one or two occasions the insect was detected reposing, and it could then be seen how completely is assimilates itself to the surrounding leaves. The little tails of the hind wing touch the branch, and form a perfect stalk to the leaf, which is supported in its place by the claws of the middle pair of feet, which are slender and inconspicuous.
The irregular outline of the wings gives exactly the perspective effect of a shrivelled leaf. We thus have size, colour, form, markings, and habits all combining together to produce a disguise which may be said to be absolutely perfect; and the protection which it affords is sufficiently indicated by the abundance of the individuals that possess it. Joseph Greene has called attention to the striking harmony between the colours of those British moths which are on the wing in autumn and winter, and the prevailing tints of nature at those seasons.
In autumn various shades of yellow and brown prevail, and he shows that out of fifty-two species that fly at this season, no less than forty-two are of corresponding colours. Orgyia antiqua, O. In winter, gray and silvery tints prevail, and the genus Chematobia and several species of Hybernia which fly during this season are of corresponding hues. No doubt if the habits of moths in a state of nature were more closely observed, we should find many cases of special protective resemblance. A few such have already been noticed. Agriopis aprilina, Acronycta psi, and many other moths which rest during the day on the north side of the trunks of trees, can with difficulty be distinguished from the gray and green lichens that cover them.
The lappet moth Gastropacha querci closely resembles both in shape and colour a brown dry leaf; and the well-known buff-tip moth, when at rest, is like the broken end of a lichen-covered branch. There are some of the small moths which exactly resemble the dung of birds dropped on leaves, and on. Bryophila Glandifera and Perla are the very image of the mortar walls on which they rest; and only this summer, in Switzerland, I amused myself for some time in watching a moth, probably Larentia tripunctaria, fluttering about quite close to me, and then alighting on a wall of the stone of the district which it so exactly matched as to be quite invisible a couple of yards off.
Caterpillars are also similarly protected. Many exactly resemble in tint the leaves they feed upon; Others are like little brown twigs, and many are so strangely marked or humped, that when motionless they can hardly be taken to be living creatures at all. Andrew Murray has remarked how closely the larva of the peacock moth Saturnia pavoniaminor harmonises in its ground colour with that of the young buds of heather on which it feeds, and that the pink spots with which it is decorated correspond with the flowers and flower-buds of the same plant.
The whole order of Orthoptera, grasshoppers, locusts, crickets, etc. This is carried to the furthest possible extent in the wonderful genus, Phyllium, the "walking lead" in which not only are the wings perfect imitations of leaves in every detail, but the thorax and legs are flat, dilated, and leaf-like; so that when the living insect is resting among the foliage on which it feeds, the closest observation is often unable to distinguish between the animal and the vegetable.
They hang loosely about shrubs in the forest, and have the extraordinary habit of stretching out their legs unsymmetrically, so as to render the deception more complete. One of these creatures obtained by myself in Borneo Ceroxylus laceratus was covered over with foliaceous excrescences of a clear olive green colour, so as exactly to resemble a stick grown over by a creeping moss or jungermannia.