Evolution Of Cognition Research Paper

1. The Functional Complexity Of The Brain And Its Processes

One of the characteristic features of living things is their complex, functionally organized structure— living things appear to be designed to solve the problems confronting them in ways that are often ingenious, elegant, and economical. Humans are no different. Indeed, the human brain is probably the paramount example of a complex, functionally organized structure in the biological world. Viewed macroscopically, there is nothing particularly remarkable about the human brain. A little more than a liter in volume, it simply looks like a wrinkled mass of tissue. However, the brain, as is now generally recognized, is a cognitive organ. It represents, stores, and processes information, and it is in the information processing abilities of the brain that its functional complexity resides. But how did the cognitive architecture of the brain arise?

One of the great puzzles of biological life is the origin of the kind of complex, functional organization that the brain so clearly illustrates. According to the laws of physics, organized systems should tend toward disorder; but biological systems are not only highly ordered, they seem to increase in complexity with time (Dawkins 1986). Ordered structures can persist, however, if they reproduce themselves faster than they fall apart. By reproducing themselves, biological entities initiate a process—evolution through natural selection—that Darwin recognized could account for ever increasing refinement of complex, functional organization. Features of an organism’s design that confer an advantage in acquiring resources for reproduction will enhance their own spread through differential reproduction. The slow accretion of such incremental improvements in the design of organisms can eventually result in the evolution of the ingenious, elegant and economical structures (called adaptations) that are so common in living things.

Because organisms in all their complexity develop from single cells, some might argue that the complex functional organization of the brain requires a developmental explanation, rather than an evolutionary one. However, the development of the brain and learning are exceedingly complicated processes, just as much in need of an evolutionary explanation as the final product, adult cognition. Development can evolve, precisely because it is repeated from generation to generation with variation in developmental trajectories, where some lead to fitness-enhancing improvements and some to less fit products. Natural selection will act on these developmental trajectories to produce ever more adaptive ones.

Moreover, an evolutionary view of cognitive development leads one to expect the same economy and efficiency of design in developmental mechanisms (Elman et al. 1996). From an evolutionary point of view, what is important is whether an adaptation develops reliably, that is, whether the trait is reproduced reliably, in the sorts of environment typical of the species. If this can be accomplished by exploiting the information structure of the environment, then there is reason to believe that natural selection would favor the use of such information. Evolution through natural selection is not synonymous with the ‘genetic coding’ of functional architecture. Darwin, after all, was able to formulate his theory of natural selection without any knowledge of genetic coding.

A corollary of this view is that what often appears to be cognitive ‘flexibility’ can, in fact, be the result of selection for developmental efficiency. Evolved mechanisms may be designed to tolerate some kinds of variation in developmental inputs, particularly variation that is not functionally relevant to the adaptive problem the mechanism solves. Consider language, for example. Modern English, Japanese, and Quechua are all evolutionarily novel inputs to the mechanisms for acquiring and processing language, yet each of these modern languages solves the problem of communication effectively, for which language abilities were presumably selected. Hence, viewed from one perspective, the developmental mechanisms are flexible in being able to accommodate a wide range of novel inputs, but viewed from another angle, they have functional design constraints that all modern languages satisfy. From an adaptationist point of view, what is important is that adults develop reliably functional competence in linguistic communication.

Rather than offering mutually exclusive accounts mental structure, development and evolution complement each other. Development provides a proximate explanation for how mental complexity is constructed during the course of a lifetime, while evolution through natural selection explains why such complex developmental processes arose over evolutionary time. Recently, there has been considerable interest in how complexity can emerge through interactions of various kinds between evolutionary and developmental processes. Such emergent phenomena admit of various kinds of explanation. Some theorists prefer to locate the explanation for emergent complexity in the local interactions that produce it. However, it is unclear whether complexity that arises in the absence of natural selection is organized functionally in a way that provides an adaptive fit between the organism and its environment. For this reason, many theorists prefer to focus on natural selection as the cause of functionally organized complexity. Adaptations are not merely complex traits, but are also organized functionally. This functional organization is observed at various levels of biological organization: biochemical, physiological, anatomical, and cognitive, with developmental mediation playing a greater role at higher levels of organization.

Regardless of the level of organization that is involved, what matters is that a trait in some way enhances its own reproduction. In the course of competing for resources, such as food, shelter, and mates, the individual is faced with many different challenges that vary with the ecological and social environments encountered. It is by virtue of its ability to solve such adaptive problems that an adaptation furthers its own reproduction, and hence is said to have the function of solving that problem (Williams 1966). Mobile species, in particular, are highly dependent upon cognitive adaptations that can interpret and integrate information in order to respond adaptively to a heterogeneous environment. The animal kingdom is filled with many striking examples of cognitive adaptation, such as the ability of Clark’s nutcrackers (Nucifraga columbiana) and other food-caching birds to recall the location of thousands of widely scattered food stores after a delay of several months (Gallistel 1990, pp. 155–8).

2. Consequences Of Cognitive Evolution

The evolutionary account of adaptation has three important consequences for cognitive functioning. The first is that traits must be evaluated from a practical, ecological perspective. Traits with no impact on an organism’s reproductive success cannot evolve through natural selection. From an evolutionary point of view, one would only expect cognitive adaptations for the sorts of problem that could conceivably have an impact on reproductive success. Typically, this will mean traits that have a real impact on the organism’s interactions with the physical, biological, and social world upon which successful reproduction ultimately depends. Natural selection, therefore, gives rise to practical cognitive mechanisms that can solve the real world problems confronting the organism. While the ability to solve evolutionarily novel tasks may indeed be beneficial, it is important to keep in mind that performance on artificial tasks, such as laboratory tasks often used in cognitive psychology, may depend on the degree to which these tasks reflect aspects of adaptive problems faced by organisms during their evolutionary history.

The second important consequence is that, in order to understand the adaptive organization of cognition, one needs to consider the past history of the species. Evolution is a slow, historical process. Complex adaptations take many generations to evolve, so the evolved design of an organism will reflect the sorts of problem that confronted ancestral members of the species and not necessarily the problems confronting the species currently. Hence, it is often useful to make a distinction between the proper and actual function of a cognitive adaptation (Millikan 1984). The proper function of an adaptation is the function that it served in ancestral environments, by virtue of which it persisted and proliferated over successive generations. The actual function of an adaptation is the use that it serves currently in a particular individual. The actual function of a mechanism may or may not correspond to its proper function. Consider object segregation in vision. The properties of light have changed very little, if at all, since the mechanisms of object segregation began to evolve in ancestral vertebrates. Hence, there is every reason to believe that object segregation in modern humans functions much as it always has: the proper and actual functions of the mechanisms are identical. Compare the situation with language. The best available evidence suggests that languages evolved as a spoken form of communication (Pinker 1994). Written language, on the other hand, shows evidence of being a relatively recent cultural invention with an origin dating to only a few thousand years ago. Reading and writing employ some of the same cognitive processes as spoken language, but this does not make reading and writing part of the proper function of these mechanisms. Reading, writing, and speech are all part of the actual function of linguistic processes, while speech alone constitutes the proper function of the mechanism. The distinction between proper and actual functions is important to bear in mind, because the structure of an evolved mechanism is best explained by its proper function, not its actual function, and mechanisms which may appear to be maladaptive in present environments might not have been so in past ones.

The third important consequence is that cognitive adaptations are exhibited universally among individuals with an identical history of selection. Although individual variation is crucial for the evolutionary process, natural selection systematically sifts through this variation, retaining those variants that are relatively beneficial and displacing those variants that are less adapted to their environment. Eventually all variation with reproductive consequences is eliminated from the species, leading to universal, speciestypical cognitive adaptations, and a residue of variation with no systematic reproductive consequences. Hence, there are three basic products of the evolutionary process that are expressed in the individual: adaptations, by-products, and random effects (Buss et al. 1998). Adaptations are complex, functionally organized structures that evolved as the accumulated product of natural selection acting on variants solving a specific problem. Adaptations often appear as though they were designed to solve specific problems, and are therefore said to show evidence of special design (Williams 1966). By-products are incidental features of adaptations that played no role in an adaptation’s selective history. Because they derive their structure from adaptations, by-products may also appear complex and functionally organized. Random effects are random features of an organism with no functional organization, no history of systematic selection, and tending to show individual differences in their expression.

3. Methods And Evidence In The Study Of Cognitive Evolution

The hallmark of adaptation by natural selection is functional specialization, or special design. In general, the principles of adaptive design are similar to the principles of good engineering: efficiency, precision, reliability, and so on. Just as the features of a well-engineered machine can be distinguished from the products of chance, so can the features of evolved adaptations (Williams 1966). To demonstrate the existence of an adaptation it is necessary to demonstrate design for a specific adaptive function, but not just complex organization per se, because it is important to distinguish adaptations from by-products. Some of the sources of evidence for special design are the following.

3.1 Laboratory Studies Of Cognition

It is useful to study an organism in its natural environment in order to understand the adaptive problems that it faces and the selection pressures operating on it. In this respect, observational studies are very important, but they have their limitations when it comes to elucidating the nature of the psychological mechanisms underlying observable behavior. For this purpose, controlled laboratory studies using methods from cognitive psychology are ideal. For example, in order to test the proposal that human resource acquisition is sensitive to variability in returns, as predicted by evolutionary theories of foraging behavior (Stephens 1981). Rode et al. (1999) employed a standard procedure used by cognitive psychologists studying people’s decision making. They offered people a choice between two gambles with the same expected return, but with more or less variability in returns. By introducing a minimal requirement that people had to satisfy in order to win any money, Rode et al. (1999) were able to manipulate whether people selected the more or less variable option in a manner predicted by Stephens’ (1981) risk sensitive foraging theory, but not by standard models of human decision-making. These laboratory studies complement nicely the observational field studies performed by human behavioral ecologists studying traditional foraging peoples (e.g., Smith and Winterhalder 1992).

3.2 Neuropsychological Dissociations

If the mind of an organism is composed of different, functionally specific adaptations, then these adaptations should, in principle, be dissociable: a particular competence may be disabled, either temporarily or permanently, while others are left largely intact. Such dissociations can be an important source of evidence for special design, because while it can be difficult for the observer to identify distinct cognitive abilities in the behavior of normally functioning individuals, the absence of a specific competence can bring its nature and boundaries into strong relief, against a backdrop of intact skills. Many such dissociations have been identified in humans, and the study of patients with particular kinds of neurological impairment has been a valuable source of data for testing hypotheses about the functional building blocks of the mind. For example, the study of autism, in which social cognition is impaired relative to nonsocial competences, has provided evidence for the existence of a variety of cognitive mechanisms whose hypothesized evolved function is to interpret and predict the behavior of others (Baron-Cohen 1995).

3.3 Developmental Studies

One reason among many for studying cognitive development is that potentially it can illuminate the functional components that underlie adult competences. Many such competences, although they appear to function seamlessly in adults, are in fact composed of separate components whose individual operation can be observed more readily in children. For example, many mammalian species orient spatially using the large-scale structure of the environment (Gallistel 1990). Adult humans use many spatial cues to orient themselves during navigation, obscuring the separate subcomponents of this competence. However, this core mammalian competence is observed more readily in young children (Hermer and Spelke 1994).

3.4 Phylogenetic Comparative Approaches

Even if one’s interest is in human cognition, there are still valuable insights to be gained from the study of nonhuman species. Such studies provide yet another way of isolating the adaptive components of cognition. For example, it has been claimed that the human adult number competence—specifically, the ability to count and perform other manipulations with numbers—is derived from a core number competence, observable in infants (Carey and Spelke 1994 see). However, such a core competence has also been found in Rhesus monkeys (Macaca mulatta) (Hauser et al. 1996), suggesting that the competence seen in human adults has other components as well.

4. Conclusion: Evolutionary Theory As Computational Theorizing

In his classic book on vision, Marr (1982) stressed the importance of beginning investigations of complex systems with a computational theory—a task analysis of the problem to be solved: What are the available inputs? What are the desired outputs? What are the constraints on the system? The answers to these questions serve as an important guide when formulating hypotheses about the cognitive mechanisms that actually solve the task. Although Marr’s theory has been highly influential in vision research where there is some intuitive appreciation of the functions of mechanisms in the visual system, his theory has not been applied as readily in other areas of psychology. The merging of Marr’s approach with insights from evolutionary theory offers promise for many areas of psychology outside perception. Evolutionary biology is a rich source of task analyses for a variety of adaptive problems that require cognitive solutions, in many practical domains. Moreover, cognitive psychology is a rich source of theoretical constructs for describing the psychological mechanisms that can solve such problems. Hence, evolutionary theorizing and cognitive psychology are well suited to play complementary roles in the study of the mind’s design.

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