Introduction to the Philosophy Underlying the Study of Animal Behavior

Barry Sinervo©1997

Index

Prehistory and an "Adaptive" Appreciation of Animal Behavior

Typological Thinking and Classical Views of Species

An Aside on Typological Thinking and Humans

Darwin's Theory of Evolution by Natural Selection

Philosophical and Theological Objections to Darwin's Theory

Darwin Formulates a Theory of Sexual Selection

The Traditions of Animal Behavior

Ethology

Psychology and Behaviorism

The Debate on Nature versus Nurture

Behavioral Ecology and Sociobiology

Ultimate versus Proximate Causes

Cause, Development, Evolution, and Function

Introduction

The study of animal behavior has Darwin's ideas concerning evolution as its core. We will first treat the development of these ideas regarding evolution by natural and sexual selection. In treating the ideas in a field, it is important to consider where these ideas came from. This gives you an appreciation of the underlying philosophy behind a field which is essential for complete comprehension of the important concepts. In our treatment of philosophy and history, we could use Darwin as a starting point for modern ideas on animal behavior, but our understanding of animal behavior undoubtedly arose during our own prehistory. Presumably we learned, or evolved an instinctive understanding of behavior because such understanding has direct survival value.

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Prehistory and an "Adaptive" Appreciation of Animal Behavior

Just as the behavior of animals evolves and is shaped by natural selection, our own understanding of behavior was probably shaped by survival needs. By better understanding the behaviors of animals, a primitive hunter in a hunter-gatherer society would be able to catch and trap game. There is of course no way to see direct evidence of such observational skills in prehistoric humans as they are no longer in existence, however, samples of cave art from 40,000+ years ago present evidence that primitive humans made observations on the animals that they hunted. For example, animals that are found in herds (e.g., horses) are typically portrayed with like members of the species, whereas animals that are typically solitary (e.g., auroch [an ancient forest dwelling oxen -- ancestor of the cow], mammoths, rhinos and bears) are portrayed alone in the paintings on caves. In some cases the solitary animals are together, but it appears that they are interacting and facing one another in some contest. Such speculations on the meaning of cave art will remain unanswered. However, if you ever have the opportunity to follow an aboriginal tracker from any of the diverse biomes that they inhabitat, I am sure that they will teach you a thing or two about animal behavior.

Primitive man could readily have exploited the behaviors associated with this behavioral dichotomy to capture prey. Animals that travel in herds could have been driven over cliffs in large numbers provided that the lead animals were first driven over the precipice. In a curious way, humans first ideas regarding behavior were undoubtedly developed for the very reasons behaviors arose in all organisms -- because such behavior has adaptive value.

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Typological Thinking and Classical Views of Species

It is a large leap from such practical considerations of animal behavior to a consideration of the study of animal behavior as a discipline. The Greeks were interested making sense of the order in the world around them and they began to consider the origin of animals species and indeed those attributes of animal species that make them unique. Embodied in the Greek version of species was the concept of type or eidos. Underlying this way of thought is the notion that there is perfect type that underlies each an every species, much in the way geometrical shapes have an ideal (e.g., equilateral triangle is the ideal of all three-sided shapes that we call triangles). One of the key aspects that differentiates species is the kinds of behaviors that they demonstrate.

Classical Greek ideas on species and an underlying type that defined species persisted until Darwin's formulation of evolution. Theologians and Academics used these ideas in their formulation of the ladder of life. For example, Carrolus Linneaus' Systemae Naturae was developed in a large measure to categorize the types of animals and also show how the "Creator" had developed a set of types that lead to higher and higher types (from slugs to man) in a ladder-like sense of perfection.

This way of thought has been referred to as typological thinking by Ernst Mayr, an evolutionary biologist who was influential in the development of the Modern Synthesis of our ideas on Evolution. By focusing on type, Greeks, subsequent theologians, and pre-Darwinian scholars all ignored the interesting differences among individuals of a single species and considered them unimportant.

In retrospect, it is not surprising that typological thinking took hold of our concept of species for so long. Species have what we in the present-day terms refer to as species-typical behaviors. Such species typical displays are most clearly seen during mating, which is "highly ritualized" and stereotyped in all animals. Animals also display other species typical behaviors during the other activities of daily life such as foraging, preening, social interactions, however, the mating behaviors are especially stereotyped as insuring that an animal mates with a member of the same species is critical (this seems so obvious, however, in terms of the origin of new species, this step is a key in the differentiation of a new species). One of the classic examples of species-typical behavior are the push-up displays of lizards. Here is an example of two male side-blotched lizards displaying <3 meg video> in rapid succession to one another.

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An Aside on Typological Thinking and Humans

Typological thinking and its application to the species question was to have a hold on to the study of organisms for two millennia until the time of Darwin. It is tempting to speculate whether or not such a stumbling block to understanding evolutionary processes and the origin of the species might actually have a biological basis in the way humans (and other organisms) process information. For example, the cognitive processes of humans may be structured in a way that is conducive to a form of stereotyping which would allow one to make sense and order the world around us. By categorizing objects and other organisms into types and sub-types we would limit the amount of information necessary to remember salient features that define a group of things. Moreover, sub-typing and typing would allow for efficient information retrieval if the type "label" is used as a handle to pull information out of long-term memory. The study of Animal Behavior has been, and will always be controversial. It is a subject that explores many "loaded questions" of biology. Such questions explore the biological basis of our own species and this example is meant to illustrate how such study might indeed have power in explaining behavior patterns in our own species.

In terms of modern human society and culture, stereotyping might have a strong downside. Many people seem to apply stereotypes to racial and ethnic groups and in most cases, such stereotyping has a definite negative effect. The application of stereotypes to one group ignores the fact that individuals are unique and this uniqueness is what should be recognized as important. Some might argue that rooting up such examples of biological determinism to behavior is going to cause troubles and it could be used as a scape-goat which divorces us from our actions. That could not be further from the aim of such research. Such research gets at the cause of behavior. Period. Just an explanation for the way the world works.

Returning to the concept of typological thinking, by locking in on the why species are the same ignores all the variation in a single species. It is in fact all of this variation that Darwin realized was important in the origin of species. This was Darwin's seminal contribution to scientific thought and it revolutionized the study of Biology, and indeed launched the discipline of Animal Behavior.

The study of animal behavior explores issues that are at the roots of why we can even ask questions about ourselves. Now this is a mind-bending concept if there was one. Are we constrained in how we think and has this limited the way we have developed ideas concerning our own human origins? How is it that the human brain evolved, and how does it enable us to ask questions about ourselves? The study of behavior and indeed the study of the brain, the source of most interesting behavior, is a field that challenges our minds to the utmost. We use our own minds to fathom the origins of our own minds. [Don't think too hard about this one or it might start to hurt].

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Darwinian Ideas on Evolution

Darwin's interest in the variation within a single species was the key shift in paradigm that revolutionized thoughts concerning evolution and by association the study of animal behavior. A paradigm is a world view or a theoretical basis, for explaining the world. Prior to Darwin's contribution, the paradigm that people operated under was that species arose by special creation, and that species were immutable (unchangeable) after this act of special creation. By asserting that organisms were non-changing the question of the origin of species or the evolution of species was de facto, a non question.

Certainly other evolutionists existed prior to Darwin. The most famous of these evolutionists was Lamarck. Lamarckian theories of species change have been caricatured in modern textbooks on evolution, but it is important to realize that Lamarck was the champion of evolutionary thought, he just happened to get the mechanisms of evolutionary change wrong. In Lamarck's theory, organisms adapt to their environment by acquiring changes in their lifetime and passing on such changes to their offspring. If such a theory operated in practice, then Arnold Schwartzenegger would tend to produce offspring with phenomenal or at least above average muscle development largely because of the characters Arnold acquired during his own youth. This is the theory of evolution by the process of the inheritance of acquired characters.

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Darwin's Theory of Evolution by Natural Selection

Darwin came up with a theory that had a non-Lamarckian basis for the the variation that leads to adaptation. Let us consider Darwin's paradigm shift in greater detail. The following is a synopsis of Darwin's formulation of the theory of evolution by the process of natural selection:

Darwin assumed that organisms naturally vary in almost every attribute that they display.
Such variation might lead to differences in survival or reproduction.
Because an excess number of progeny are produced in all organisms, there is a competition amongst them to produce successful progeny, or what Darwin called a "struggle for existence."
If the variation that leads to differences in survival or reproduction is heritable, then those individuals that produce the most progeny will also tend to have offspring that resemble the parents, and the species will evolve by a process that Darwin referred to as natural selection.
New species arise from old species by the acquisition of slow changes in traits, behavioral traits included, and such changes are driven by the blind force of natural selection.

The key to Darwin's argument is that there are heritable differences among individuals of a single species, and that such differences lead to heritable changes from generation to generation, ultimately leading to evolutionary changes in the species or perhaps the origin of an entirely new species. This is dramatically different from typological thinking in which similarity among species is the focus of attention. By focusing on the minute differences among individuals of a species Darwin came up with the mechanism of natural selection -- the driving force behind evolutionary change. However, evolution by natural selection is really blind, because the ultimate source of all genetic variation, the raw material for natural selection, is the process of mutation.

This is why natural selection is described above as being blind. At its core, natural selection is what is referred to as a stochastic process. Individuals die and survive and reproduce as a function of their traits, but it is a probabilistic outcome. In the same way, mutations arise in a probabilistic fashion. Sometimes the mutations are beneficial, but, more often than not the mutations are detrimental and such detrimental mutations are weeded out by natural selection. Natural selection tends to sift out those beneficial mutations that tend to arise only rarely in a population. It is not necessarily the case that a beneficial mutation will be passed on to subsequent generations. What if the bearer of the mutation does not pass on that copy of the gene to its offspring.

Probability of a beneficial mutation making it through segragation

Remember that diploid organisms have two copies of each gene, and the beneficial mutation only has 50% chance of being passed on to each offspring. If an organisms with a beneficial mutation has four progeny, then there is a probability that no progeny receive the beneficial mutation and that probability is given by:

1/2 x 1/2 x 1/2 x 1/2 = 1/16.

Each of the progeny has a 1/2 chance of not getting the gene. The probability of one offspring not getting the beneficial mutation is independent of the other offspring not getting the gene and by the laws of probability we multiply successive independent events to achieve the probability that no progeny get the beneficial mutation. If the unique beneficial mutation is not passed on to the progeny then more time will be required to see yet another beneficial mutation arise in the population before natural selection can promote its spread.

Darwin formulated his ideas concerning natural selection over the course of many years, and his voyages on the "Beagle" in which he was charged with collecting species on a world tour, seemed to provide Darwin with a time to generate raw natural history observations on species. Upon returning to England, Darwin began to sketch his ideas on evolution in several "sketch books". He held onto his ideas for nearly 20 years before publishing it, and he only moved to publish because of the fear of being scooped. Alfred Russell Wallace had sent Darwin a manuscript to read and Wallace was asking Darwin's advice on the manuscript before he presented to the scientific community. Darwin then moved to publish and Wallace and Darwin communicated a joint paper to the Royal Society's meetings during 1858 in which the advocated their ideas concerning the role of natural selection in evolution. Darwin (1858) then published his famous "On the Origin of the Species" and this set of a firestorm of controversy in the Victorian world that was England.

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Philosophical and Theological Objections to Darwin's Theory

What was very controversial to the lay public and some scientists alike was that Darwin stated that humans were subject to the same biological process as all animals. Application of evolutionary theory to humans even in todays world elicits a similar controversy. Another aspect of controversy was the notion that evolution has no direction, no progress, natural selection is a purely blind and mechanical process. The relentless elimination of less fit variants ran against the notion of a design in nature. These philosophical objections are wonderfully summarized by John Dewey (1909) a contemporary philosopher:

"The Darwinian principle of natural selection cut straight under this philosophy [that of design]. If all organic adaptations are due simply to constant variation and the elimination of those variations which are harmful in the struggle for existence that is brought about by excessive reproduction, there is no call for a prior intelligent causal force to plan and preordain them. Hostile critics charged Darwin with materialism and with making chance the cause of the universe."

The impact of Darwin's Theory of Evolution by Natural Selection on Society was immediate, dramatic, and long-lasting -- a few examples:

Social Darwinism (1890's) was formulated, and attempts were made to link social change via competition, (e.g., Adam Smith) with evolution (Darwin described such comparisons as foolish).
Karl Marx used Darwin's theory of the law of development of organic nature for his ideas on the law of development of human history (technological evolution). Marx dedicated a copy of Das Kapital to Darwin.
Later (1930's), the notion of fittest was used to rationalize eugenics (e.g., Nazi party in Germany are the most notorious, however, the movement was worldwide) and resulted in the mass murder of millions. Even in the United States, some individual states had sterilization laws on the books, for "feeble-mindedness" until the late 1950's.
In a reaction to Eugenics, Lysenkoism arose to prominence in the Soviet Union (Lysenko was an agricultural advisor of Stalin). Lysenko had neo-Larmarkian views on the role of environment and species change and these views dominated Soviet agriculture through the 1950's (many geneticists were imprisoned during his power). Denunciation of genetics by communism).
Modern ideas arose concerning the "selfish gene" in human evolution and society. More recently, we have seen the emergence of the discipline of evolutionary psychology, which applies the ideas of behavioral ecology on animals to the human species.
Modern ideas concerning cultural evolution arose in part as a reaction to the notion that all human behavior is genetically based. For example, human culture can evolve by non-genetic transmission of ideas (see above). Because, culture forms the basis for many aspects of behavior, it is argued that environment plays a major role in shaping our (collective) psyches.

The application of evolutionary theory to humans and ethics is succinctly summarized by T. H. Huxley in an essay he wrote on Evolution and Ethics (1893). Just as an aside, Huxley was noteworthy as the champion of Evolutionary Theory in a famous debate with Bishop Wilberforce.

"There is another fallacy which appears to me to pervade the so-called 'ethics of evolution'. It is the notion that because, on the whole, animals and plants have advanced in perfection of organization by means of the struggle for existence and the consequent 'survival of the fittest'; therefore men in society, men as ethical beings, must look to the same process to help them towards perfection. I suspect this fallacy has arisen out of the unfortunate ambiguity of the phrase 'survival of the fittest'. 'Fittest' has a connotation of 'best'; and about 'best' there hangs a moral flavour. In cosmic nature, however, what is 'fittest' depends on conditions."

As we will find out in subsequent readings, natural selection could operate on aspects related to "human morality", but the defining process underlying much of human behavioral evolution is that selection leads to patterns of behavior that benefit the individual or the "inclusive fitness of the individual" that would include the individuals closely related kin.

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Darwin Formulates a Theory of Sexual Selection

Darwin did not let the uproar die down for too long, before he published (1871) yet another controversial book entitled "The Descent of Man and Selection in Relation to Sex". If Darwin's theory of evolution forms the core of evolutionary theory, we could consider this book the core to Animal Behavior and really the first book to treat problems of animal behavior within this new evolutionary framework. Darwin attempted to explain many curious puzzles regarding animal behavior and morphology in animals, in addition to the origin of emotions and thought in man. Darwin realized that traits related directly to reproduction, in particular mate choice or competition for mates, were distinctly different from other traits under natural selection (e.g., foraging ability) and he coined a new term for them -- sexual selection.

The theory of sexual selection could explain why certain traits that appeared to have little survival value or perhaps were even maladaptive, could evolve. For example, why does a male peacock drag around an elaborate, expensive-to-produce tail which might even lead to a higher risk of predation? In another example, the bower bird constructs an elaborate bower, which he decorates with "flashy items". The sole function of the bower is to entice females into copulation. If such traits, increase the number of mates that a male gets then such sexual selection could overwhelm the force of natural selection and traits that appear to be maladaptive could spread through the population. We will consider Darwin's theory of sexual selection in great detail in subsequent sections, but for the moment we will define sexual selection to distinct from natural selection and consider it to be variation in mating success among individuals in a population that arises from either:

the choices that females make regarding showy ornaments that males display, or
male-male competition for females.

Darwin had formulated a theory of natural and sexual selection that has stood the test of time. A revolution occurred in biology in which everybody accepted that evolution took place, and Darwin can be credited with initiating that revolution. Surprisingly, scientists did not accept that evolution took place by the process of natural and sexual selection, and this issue was not resolved until long after Darwin's death in 1893. Just as an aside, Darwin did not get everything correct. First, he did not have the proper mechanism for transmission of genetic variation across generations. Darwin did not know that differences in the two alleles at a genetic locus formed the basis for variation, which was discovered by Gregor Mendel. Second, Darwin did not understand how new genetic variation was created. A mutation at one copy of the allele yields new genetic variation, and Hugo de Vries credited with formulating a theory of mutation or "mutationstheorie". Because Darwin missed these key points, his theory of natural selection did not gain the widespread acceptance in the scientific community that it now garners today.

The Neo-Darwinian Synthesis, which occurred after 1910 brought together all the opposing views into a single unified theory of evolution. Evolution occurs by natural selection. However, natural selection depletes genetic variation, and new heritable variation that natural selection can act upon arises by the process of mutation. Major players in the neo-Darwinian synthesis include the theoreticians Ronald Fisher, Sewall Wright and J. B. S. Haldane who developed a mathematical formulation for evolution that seemed to add much needed rigor to the arguments. Ronald Fisher also went on to elaborate on Darwin's theory of Sexual Selection and illustrated the fundamental reason why natural selection should be distinct from sexual selection. We will consider the details of this theory later, but the gist of his ideas is that sexual selection can lead to a runaway process in which females choose ever showier males even if such choices have strong maladaptive consequences for male survival.

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The Traditions of Animal Behavior

Ethology

The study of animal behavior per se, also has a tradition that stretches beyond the time of Darwin. The field of ethology, the study of the evolution and functional significance of behavior originates with C. O. Whitman in the 1800's. Whitman studied the display patterns of pigeons and coined the term instinct to describe such behaviors. The ethogram or a graphing of the time course or switch points in a behavioral series became a way of categorizing species differences in behavior. Many of these instincts are triggered by various environmental stimuli and von Uexkull termed such triggers of instinctive stereotyped behaviors sign stimuli.

A classic sign stimulus (see 3 Meg video) triggers the courtship display of male three-spined sticklebacks. The enlarged belly of a female triggers the zig-zag dance in male sticklebacks and this dance is used to entice the female to enter the nest that the male has built. In this video, the male is more likely to court a super gravid dummy (a more extreme or supernormal sign stimulus) than the normal gravid dummy. Jenny Jenkins of Indiana University set up this encounter of a male and two dummy females which differ in the degree of enlargement of the belly.

Much of the work of early ethologists was synthesized by two Nobel Laureates, Niko Tinbergen and Konrad Lorenz. Lorenz is noted for his work on genetically programmed behaviors in young and for studies on imprinting, during critical developmental periods in young. A classic example of imprinting occurs in goslings when they form an image of parent just after hatching and if they first encounter a human (such as Konrad) they will imprint on him and follow him around as if he were their mother. A third Nobel Laureate, Karl von Frisch, pioneered studies in bee communication and foraging.

Tinbergen's seminal contribution to Behavior was to formulate a method studying animal behavior, and this method forms the basis for how I have structured my presentation of material. Tinbergen listed four areas of inquiry that could be used to understand issues of animal behavior. The following mnemonic can be used to remember these four areas ABCDEF:

A -- Animal

B -- Behavior

C -- Causation

D -- Development

E -- Evolution

F -- Function

Causation refers to the proximate causes of behavior such as the hormones, genes, nerve impulses that control the expression of behaviors. Development refers to the ontogeny of behaviors such as imprinting, or in the case of cognition, issues of learning. Evolution refers to the phylogenetic context in which the behaviors are found. For example, the prevalence of parental care in birds, but not reptiles (with some exceptions) is an example of the taxonomic affiliations of some behaviors. Function refers to the adaptive value or contribution that the behavior makes to fitness.

These issues are central to developing a philosophical approach to animal behavior and to the structure of these lectures and I treat this in greater detail below. The ethological approach had a strong Darwinian tradition underlying its development, and as such much of the work was aimed at understanding the ultimate evolutionary reasons for behavior.

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Psychology and Behaviorism

The ethological approach typified by the studies of Lorenz, Tinbergen, and von Frisch was largely concerned with the workings of organisms and their environment. A large group of scientists were also concerned with the study of animal behavior, but the focus for these researchers was on model organisms (e.g., Norway rat) in a controlled laboratory setting. The focus of much of this work was aimed at answering the mechanistic underpinnings of behavior. Classic work by B. F. Skinner lead to the development of the paradigms of learning, the Skinner Box remains a vital tool in animal psychology.

This included a rich development of research involving the psychological sciences and include the following topical areas:

perceptual psychology -- reception of environmental stimuli through the senses, and subjective perceptual interpretation of these sensory stimuli,
physiological psychology -- an attempt to relate physiological properties within an organism to external behaviors (e.g., measuring nerve impulse transmission in sensory and motor nerves),
functionalism -- a study of the mind (e.g., John Dewey) and how the mind operates.
behaviorism -- a study of how experiences accumulate in an animal and are written on the tabula rasa or blank slate that is found at birth,
animal psychology -- initially related to the study of learning, but in modern form encompasses a large body of work related to cognition in a diverse group of animals.

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The Debate on Nature versus Nurture

These fields of animal psychology, which originated in America, viewed behaviors as being largely the product of the environment. In contrast, the field of ethology, which originated in Europe, looked to the genetic underpinnings of behavior. Differences between the ethology and animal psychology led to a debate on the causes of behavior that has been captured in the phrase "nature versus nature". Are the behaviors seen in organisms a product of their genetic background, or their environment? As we will see, despite the controversial nature of this debate, it is not an answer that can be simply answered in terms of either one or the other, but behavior can be the result of a complex interaction between genes and the environment.

Behavioral Ecology and Sociobiology

Students of Behavioral Ecology have attempted to synthesize both the evolutionary traditions of Ethology, and the mechanistic studies of Comparative Psychology. This is a relatively new movement compared to ethology and psychology and has developed over the last decade. The study of behavioral ecology focuses on organisms interacting in natural environments. Researchers are interested in both the mechanistic underpinnings of behavior, but they are also interested in the fitness consequences of such behavioral traits. This tradition could be traced by to Tinbergen as his four study areas (Causation, Development, Evolution and Function) seem to best approximate the breadth of questions addressed by behavioral ecologists. Behavioral ecology is not limited to questions of behavior, but draws in issues of energetics and physiology as these factors are often used as proxies for the fitness traits (e.g., differences in survival and reproduction) that are of interest to behavioral ecologists.

The newest approach to studying behavior involves a consideration of social systems in a diverse group of organisms. This field has taken off since the publication of Sociobiology by E. O. Wilson. As many of these ideas have been applied to humans, the theory has been the target of much controversy. Sociobiology attempts to develop rules that explain the evolution of social systems and as such it has a strong Darwinian Tradition.

More recently, the field of Evolutionary Psychology has arisen and has applied all the traditions and arguments that are used to study social animals directly to the behavior of humans. The approaches of behavioral ecology and sociobiology have been used to explain the adaptive origins of human behaviors as diverse as foraging, to siblicide, to female choice. Humans are considered subject to the same "organic rules" that other organisms operate under.

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Ultimate versus Proximate Causes

The dichotomy between Ethology with its concern of adaptation, and Comparative Psychology with its concern for mechanism can be succinctly described as a concern for ultimate versus proximate causes. Ernst Mayr describe the pursuit of those ultimate causes as a concern for the "Why Questions." Why does a bird give parental care? Why is a bee brightly colored? In contrast, the pursuit of proximate causes is concerned with the way the world works or the "How Questions." How does a bat transmit echoes? How do nerves carry impulses? Where are memories stored?

Tinbergen's four study areas also block out into ultimate versus proximate causation. For example, causation in Tinbergen's view is concerned with Proximate Causation or mechanism. Development is also considered to be in the category of proximate cause. However, evolution or phylogenetic context is squarely in the field of ultimate cause, as is the issue of function as such issues of adaptive value or fitness are directly related to evolution and evolutionary change. Our study of animal behavior begins with a consideration of the ultimate causes of evolutionary change -- adaptation and natural selection.

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Cause, Development, Evolution, and Function

Tinbergen's breakdown can be used as useful summary of the material covered thus far. I prefer to make the breakdown a little more detailed and my breakdown includes other approaches that have been added more recently by Behavioral Ecologists and Sociobiologists: Genes, Ecology, Physiology, Development and Learning, Evolution, and Sociality. My breakdown is slightly finer than Tinbergen's but it also provides the structure for this text and a schema for understanding the process of adaptation in behaviors at a variety of temporal scales. Paul Sherman (1988) would add yet another category to the list -- Cognition. However, as cognitive theory is an outgrowth of development and learning, I will include it in those categories. Cognition in Behavioral Ecology is undergoing a large-scale renaissance as researchers attempt to move the classically-developed ideas of Psychology into wild populations.

The first two subjects in the sequence Genes and Ecology will cover the basics of Darwinian natural and sexual selection as it applies to animal behavior. To further cope with environmental variation, the organism evolves adaptations of physiology that promote successful survival or reproduction. Such physiological changes could act at the level of endocrinology, neurophysiology, metabolism, or any of the myriad proximate mechanisms that operate in an organism. These proximate mechanisms are used to help the organism cope with both abiotic (e.g., the extremes of weather, navigation, etc.) and biotic environmental factors (e.g., the social environment, predation, etc.). An additional component to an organisms life are the developmental changes and learning that occur from ovum/sperm to maturity that are also adaptations to a particular way of life. Whereas physiology operates in the very short term, development unfolds during the lifespan of an organism. With an understanding of these genetic, ecological, physiological, developmental and cognitive processes in hand we will be ready to tackle the concepts of the evolution of behavior per se.

Constraints on the Evolution of Behavior

Up to this point, I have operated under the premise that adaptation is the sole process that governs the evolution of behavior. However, in recent years, students of animal behavior have become more sensitive to the limitations of organic systems to change in an evolutionary sense. Organisms may be well adapted, but such adaptation is constrained by limitations in organismal design. Such constraints on organisms reside at the level of proximate mechanism. In addition, organisms are also constrained by the effects of history or their own phylogeny.

For example, all birds lay eggs and this is because the ancestors of birds, some reptile-like dinosaur, also laid eggs. However, mammals are live bearers and this is because in the remote past a new kind of mammal-like reptile evolved a different mode of life and this novel trait was passed on to all subsequent species in the lineage or phylogeny. A famous exception to this mammalian generalization includes the monotreme mammals of Australia, the platypus and echidna. It is thought that the monotremes branched off from the main stock of mammals so early in the past that they retain the more ancestral mode of egg-laying reproduction. Such differences in reproduction constrain both birds and mammals in terms of the kind of parental care behaviors that evolve in each group. For example, many bird species have evolved male and female parental care, because rearing of the young can be accomplished by both parents. In contrast, evolution of the mammary gland as the primary source of nutrition, tends to lead to species of mammals displaying a preponderance of maternal care, and there are far fewer examples of male care in mammals. In order to understand such phylogenetic constraints, we need a working knowledge of the proximate mechanisms, as well as the process of natural selection. Accordingly, I leave the discussion of such higher order macroevolutionary process until late in the book.

Finally, I leave the discussion of sociality until the very end, because it includes even more complex interactions that occur between organisms. The added complexity of sociality makes the study of behavior very rich indeed. Just a simple example will suffice. In our developing paradigm for animal behavior, we have assumed that all changes that are passed on between generations are largely genetic and that populations evolve and genes change by the process of natural and sexual selection because behavioral traits have a genetic basis. Social evolution and the advent of culture introduces another mode of longstanding transmission of behavioral traits between generations. For example, consider humans and the advent of libraries. Libraries are a vehicle whereby information is passed on to subsequent generations of humans, but there is no genetic basis to libraries. The theory of cultural evolution holds that many behavioral changes in humans might have a large non-genetic component that arises from such cultural transmission of information.

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