Copyright © 2006 by Allyn and Bacon Chapter 2 Evolution, Genetics, and Experience Thinking about...

Copyright © 2006 by Allyn and Bacon

Chapter 2 Evolution, Genetics, and

ExperienceThinking about the Biology of Behavior

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From Dichotomies to Relations and Interactions


Is it physiological or psychological?

Descartes


Is it inherited or is it learned?


Is the “nature-nurture” debate alive today?


Problems with Traditional Dichotomies – Mind-brain dualism

Brain damage impacts psychological functioning


Problems with Traditional Dichotomies – Nature-or-nurture

“


A model of the biology of behavior

All behavior is the product of the interaction of three factors:GenesExperiencePerception of the current

situation


Thinking about Human Evolution

Evolution does not proceed in a single line.

Humans have only been around for a brief period of time.

Rapid evolutionary changes do occur. Fewer than 1% of all known species

are still in existence.



Evolution is a tinkerer, not an architect – results are not perfect.

Not all existing behaviors or structures are adaptive.Spandrels – incidental non-adaptive by-

products (such as the human belly button)



Not all existing adaptive characteristics evolved to perform their current function.Exaptions – evolved to do one thing, but now

do something else (such as bird wings) Similarities among species do not

necessarily mean that the species have common origins.



Homologous structures – similar structures due to a common evolutionary origin

Analogous structures – similar structures without a common origin

Convergent evolution – the evolution of similar solutions to the same enivironmental demands by unrelated species


Evolution of the Human Brain

There is no relationship between brain size and intelligence.

Brain size is generally correlated with body size.

More informative to look at relative size of different brain regions.



Brain stem regulates reflex activities that are critical for survival.

Cerebrum is involved in complex adaptive processes such as learning, perception, and motivation.



The human brain has increased in size during evolution.

Most of the increase in size has occurred in the cerebrum.

Increased convolutions in the cerebrum have served to increase the volume of the cerebral cortex.


Fundamental Genetics

Dichotomous traits

True-breeding lines

Mendel studied dichotomous traits in true-breeding lines of pea plants


Mendel’s Experiments

Crossed a line bred true for brown seeds with one bred true for white

First generation offspring all had brown seeds

When the first generation were bred, the result was ¾ brown and ¼ white seeds.



True-breeding linesWhite (ww)Brown (BB)

Brown was the dominant trait, appearing in all of the 1st generation offspring (Bw)



Phenotype – Genotype –



gene alleles Homozygous Heterozygous


Chromosomes, Reproduction, and Linkage Genes Chromosomes Meiosis


Chromosomes, Reproduction, and Linkage Gametes, eggs and sperm, are produced

by meiosis When egg and sperm combine to form a

fertilized egg (zygote), 23 pairs of chromosomes are again present

Mitosis – a form of cell division that yields daughter cells that have 23 pairs of chromosomes


Chromosomes, Reproduction, and Linkage Meiosis leads to diversity as the 23 pairs

of chromosomes are randomly sorted into the 2 gametes produced

Linkage – the tendency of traits encoded on the same chromosome to be inherited together

Crossing over – increases diversity, “shuffles the genetic deck”


Sex Chromosomes and Sex-Linked Traits Sex chromosomes, X and Y, look different and

carry different genes Female = XX Male = XY

Sex-linked traits - influenced by genes on the sex chromosomes

Dominant traits on the X chromosome will be seen more commonly in females, recessive ones in males


The Interaction of Genetic Factors and ExperienceOntogeny –Phylogeny –Ontogenetic development is a product

of gene-experience

Copyright © 2006 by Allyn and Bacon Chapter 2 Evolution, Genetics, and Experience Thinking about...

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