Ch. 3 Evolution, genes, environment and behavior

Ch. 3 Evolution, genes, environment and behavior

Evolution by natural selection

• Biological evolution refers to
• gradual change in organic life that may culminate in the emergence of new
• species. Charles Darwin was the first person to suggest a viable mechanism by
• which evolution could occur: natural selection.
• Natural selection is based upon
• biological variation, high reproduction and mortality rates and competition
• over limited resources. If a biologically variable and heritable trait conveys
• an advantage in terms of higher reproductive success that trait will increase
• in frequency in a given population.
• Genetic mutation is necessary
• if biological variation is to exceed the sum of a trait found in the parental
• stock of population.

Mendellian genetics

• Gregor Mendel showed how
• inheritance could occur without eliminating biological variation. In elegant
• breeding experiments with pea plants, he laid down the foundations of genetic
• science.
• Since Mendel, scientists have
• uncovered many of the details of the molecular and biochemical processes
• underlying genetic inheritance. We know now that genes are segments of
• deoxyribonucleic acid or DNA that encode for particular proteins.
• Some inherited traits are
• monogenic (based upon the influence of one gene). However, complex traits such
• as intelligence and personality are most probably polygenic (based upon the
• influence of many genes). However, all genetically influenced traits interact
• with environmental influences.
• 

Inherited behavioural adaptations

• The environment exerts its
• effects largely through processes of learning that are made possible by innate
• biological mechanisms. Humans and other organisms can learn which stimuli are
• important and which responses are likely to result in goal attainment.
• Since learning always occurs
• within environments, it is important to distinguish between different kinds of
• environments. Behavioural genetics researchers make an important distinction
• between shared and unshared environmental influences.

Behavioural genetics

• Hereditary potential is carried
• in the genes, whose commands trigger the production of proteins that control
• body structures and processes. Genotype (genetic structure) and phenotype
• (outward appearance) are not identical, in part because some genes are dominant
• while others are recessive. Many characteristics are polygenic in origin, that
• is, they are influenced by the interactions of multiple genes.
• Behavioural geneticists study
• how genetic and environmental factors contribute to the development of
• psychological traits and behaviours. Adoption and twin studies are the major
• research methods used to disentangle hereditary and environmental factors.
• Especially useful is the study of identical and fraternal twins who were
• separated early in life and raised in different environments. Identical twins
• are more similar on a host of psychological characteristics, even when reared
• apart. Many psychological characteristics have appreciable heritability.

Diapositiva 6

• Intelligence has a strong
• genetic basis, with heritability, coefficients in the .50 to .70 range. Shared
• family environment is also important (particularly at lower socio-ecpnomic
• levels), as are educational experiences.
• Personality also has a genetic
• contribution, though not as strong as that for intelligence. In contrast to
• intelligence, shared family environment seems to have no impact on the
• development of personality traits. Unshared individual experiences are far more
• important environmental determinants.

Gene-environment interactions

• Genetic and environmental factors
• rarely operate alone; they interact with one another in important ways. Genetic
• factors may influence how different people experience the same environment, and
• the environment can influence how genes express themselves.
• Genetic factors can influence
• the environment in three important ways. First, genes shared by parents and
• children may be expressed in the parents’ behaviours and the environment they
• create. Second, genes may produce characteristics that influence responses
• evoked from others. Finally, people may self-select or create environments that
• are consistent with their genetic characteristics.

Genetic manipulation and control

• Genetic and environmental
• factors interact in complex ways to influence phenotypic characteristics.
• Genetic reaction range sets upper and lower limits for the impact of
• environmental factors. Where intelligence is concerned, environmental factors
• may create differences as large as 20 IQ points. Genotype can influence the
• kind of environments to which children are exposed, as when intelligent parents
• create an enriched environment. Genetically influenced behaviour patterns also
• have an evocative influence, influencing how the environment responds to the
• person. Finally, people often select environments that match genetically
• influenced personal characteristics.
• Genetic manipulation allows
• scientists to duplicate and alter genetic material or, potentially, to repair
• dysfunctional genes. These procedures promise ground-breaking advances in
• understanding genetic mechanisms and in treating physical and psychological
• disorders. Moreover, our ability to analyse people’s genotypes allows for
• genetic screening and raises a host of practical and ethical issues.

Evolution and human nature

• Evolutionary psychology focuses
• on biologically based mechanisms sculpted by evolutionary forces as solutions
• to the problems of adaptation faced by species. Some of these genetically based
• mechanisms are general (e.g., the ability to learn from the consequences of our
• behaviour), whereas others are thought to be domain-specific, devoted to
• solving specific problems, such as mate selection.
• Evolution is a change over time
• in the frequency with which particular genes, and the characteristics they
• produce, occur within an interbreeding population. Evolution represents an
• interaction between biological and environmental factors.
• The cornerstone of Darwin’s
• theory of evolution is the principle of natural selection. According to this
• principle, biologically based characteristics that contribute to survival and
• reproductive success increase in the population over time because those who
• lack the characteristics are less likely to pass on their genes.
• -
• Among the aspects of human
• behaviour that have received evolutionary explanations are human mate selection
• and personality traits. In research on mate selection, evolutionary
• explanations have been tested against hypotheses derived from social structure
• theory, which emphasizes the role of cultural factors.