Chapter 15: Evolution and Human Behaviour

Why Evolution Is Relevant to Human Behaviour

The application of evolutionary principles to understanding human behaviour is controversial

All phenotypic traits, including behavioural traits, reflect the interactions between genes and the environment

The nature-nurture debate is based on a false dichotomy

It assumes that there is a clear distinction between the effects of genes and the effects of the environment

However, gene are not like blueprints that specify phenotype

Every trait results from the interaction of a genetic program with the environment

The expression of any genotype always depends on the environment

The expression of behavioural traits is usually more sensitive to environmental conditions than is the expression of morphological and physiological traits

Traits that develop uniformly in a wide range of environments, such as finger numbers, are said to be canalized

Traits that vary in response to environmental cues, such as subsistence strategies, are said to be plastic

Every trait however, results from the unfolding of a developmental program in a particular environment

Natural selection can shape developmental processes so that organisms develop different adaptive behaviours in different environments

There is a misunderstanding that natural selection cannot create adaptations unless behavioural differences between individuals are caused by genetic differences

If this were true, adaptive explanations of human behaviour must be invalid because there is no doubt that most of the variation in behavioural traits, such as foraging strategies, is not due to genetic differences, but is instead the product of learning and culture
Belief is false because natural selection shapes learning mechanism so that organisms adjust their behaviour to local conditions in an adaptive way
Ex. Male soapberry bugs guard their mates when females are scarce, but not when females are abundant
Individual males vary their behaviour adaptively in response to local sex ratio
In order for this flexibility in behaviour to evolve, there had to be small genetic differences in male propensity to guard a mated female and small genetic differences in how mate guarding is influenced by local sex ratio
If such variation exists, then natural selection can mold responses of males so that they are locally adaptive
In any given population, most of the observed behavioural variation is due to fact that individual males respond adaptively to environmental cues

The crucial point is that evolutionary approaches do not imply that differences in behaviours among humans are product of genetic differences between individuals

Understanding How We Think

Evolutionary analyses provide important insights about how our brains are designed

Natural selection hasn't just made our brains big, it has shaped our cognitive abilities in very specific ways and molded the way we think

Even the most flexible strategies are based on special-purpose psychological mechanisms

A considerable body of empirical evidence indicates that animals are predisposed to learn some things and not others

Ex. Rats quickly learn to avoid novel foods that make them sick
Based solely on taste of a food that has made them sick, not the food's size, shape, colour or other attributes
Makes sense because rats live in a very wide range of environments, where they frequently encounter new foods and usually forage at night when it is dark

There are certain limits to the flexibility of this learning mechanism
Certain items that rats will never sample and in this way their diet is rigidly controlled by genes
Learning process not affected equally by all environmental contingencies
Ex. Rats are affected more by the association of novel tastes with gastric distress than they are with other possible associations

Our brains may be designed to solve the kinds of problems that our ancestors faced when they lived in