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PSYB65 chapter 12.docx

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Ted Petit

PSYB65 Chapter 12 - Evolution = variation, inheritance, differential reproduction - Darwin suggested these mechanisms happen because of natural selection. Which requires all individuals that have reproductive advantage will result in magnification of these traits in population. - When trait results in reproductive advantage it’s called adaptation - Sexual selection o Intersexual selection – choosing mate based on traits o Intrasexual selection – members of same sex compete for partners of opposite sex - Original theory of evolution is called the historical theory of evolution Modern synthesis is what we refer to the current version of evolution - It is based on what we know about genes, DNA, chromosomes and population biology - We have 23 pairs of chromosomes, we have about 26000 to 40000 genes - Genotype is your genetic composition and is invariant during lifetime - Phenotype is your genotype and environment interaction. - Only genotype is passed on to children - Genes don’t make traits, they make proteins. - More than one form of a given gene – alleles. There is allele for different characteristic that makes protein for it - Mendel discovered inheritance through dominant and recessive alleles - Both alleles are same = homozygous - 2 alleles are different = heterozygous - But genes are not simplistic, it takes multiple genes to affect a trait – polygenic - Genes usually go together (brown hair + brown eyes, blonde hair + blue eyes) - Inherited traits are most likely polygenic traits - Modern synthesis o Certain environments select certain phenotypes o Although genes occur at the level fo individual, evolutionary change occurs at level of populations o Species represent different gene pools, rather than fundamentally unique groups. Focus on genotype rather than phenotype - Difference between modern synthetic theory and historical evolutionary theory: o Modern theory recognizes traits are results of genes inherited by parents and interact with environment o Recognition that there are mechanisms rather than natural selection that effect evolutionary change o Recognition that species are only differences in gene pools not totally distinct or new organisms out of nowhere Evolution of the nervous system - Brain deteriorates quickly so it does not fossilize - Only way to examine brains is looking at fossilized skulls. - Skull size has increased over time, but it’s not skull size that leads to “humanness” . eg. The tree shrew has a bigger brain to body ratio than us - it’s the increase in cortex that increases ability to perform complex behaviours - Another way to examine skull is to make an endocast/mold. That way you can look at major sulci and gyri o found that brains are asymmetrical and degree of asymmetry has increased over time. o Frontal lobe development has been associated with language o Switch from olfactory analyssi to complex reasoning tasks (switch form olfactory to frontal lobe). Largest change is in parietal lobe, became more rounded and increased size. Associated with tool making and hunting o However endocast not that reliable because there are few and it could just be due to individual variation - Studying our relatives like the chimp also show less hemispheric asymmetry, reduced frontal linguistic area, and smaller parietal lobes o Relative size of brainstem and cortex also different - Comparisons of brainstem focus on 3 major points of difference among species o Newer species have larger brains o Increase
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