course book biol. psy : Darwinism, variation, heridity, competition & natural selection

main topics

In which book is the theory of evolution explained

“on the origin of species by means of natural selection”

Which 2 major problems on the understanding of livings things does the theory of natural evolution solve?

1) problem of history

2) problem of design

Solvation in terms of eachother by natural selection: organisms have the design they have because of their history & the history they have primarly because of changes in their design and natural selection is the causal mechanism

problem of history

where do all the types of organisms come from?

• one single ancestral from which all current forms have decendent

Problem of design

Q: Why do organisms have well designed characteristics for the requirements of living that they have/tasks they have to perform? 

A: cummulative effect of non-random survival of beneficial characteristics

Hierarchial organization in nature

two species that are similar in the details of system A tend also to be more similar in the details of system B

Modern thesis

Darwins theory integrated with Mendel’s genetics: natural selection = changes in the relative frequencies of different forms of genes (alleles) in the population over generations

homologies & analogies

homologies = common origin

analogies = convergent evolution

genes

functional unit: sequences of DNA bases that code for proteins

• 25.000 genes in humans

• only 1% of the human genome actually codes for proteins

the genotype gives rise to … (2)

1) phenotype

2) genotype of the next generation

Ultimate origin of genetic variaton = ?

mutation

• many mutations have no phenotypic effect (bcs they occur in non-coding DNA), but the ones that have one are often deleterious

  • why deleterious?

    • mutation = undirected : effect of mutation is totally unrelated to the physiological needs & functions of the phenotype

      • The phenotype is already a fairly well- functioning system thanks to evolution => undirected modification of some part is thus much more likely to make it function less well than it is to make it function better 

• occur during mitosis & meiosis

behaviour is part of the phenotype => idea of ‘genes for behaviour’ = legitimate

from genotype to phenotype

genes (sequences of DNA bases) —> proteins (sequences of amino acids) —> bodies

diploid

individuals who have 2 copies of each gene

mendelian diseases

single gene diseases

genome size doesn’t correlate directly with complexity

In eukaryotes, as complexity increases:

• Proportion of coding DNA decraeses (exons)

• Proportion of introns, intergenic regions, and repetitive sequences increases

Polygenic traits

In these traits variation in the phenotype is related to which allele is present across a number of genes (eg. height)

• underlying genes are much harder to reliably localize than those underlying Mendelian diseases

incomplete dominance

the phenotype of the heterozygote is intermediate in form between those of the two homozygotes

• eg. homoz. red carnations crossed with homoz. white ones → heterozygotes with pink flowers

  • not the same as blending inheritance!! (only the phenotypic effects have been blended - not the underlying alleles) => in the next generation pure white/red is again possible

Genetic drift

= in small populations alleles will fluctuate dramatically from generation to generation

• occasionaly a new mutation will fluctuate all the way to fixation

  • P(fixation) = 1/(2N)

neutral theory of molecular evolution

the amount of divergences between the DNA sequences of any two populations basically reflects the time since their common ancestor

Heritability within vs between species

High heritability within a population does not imply that differences between populations are genetic 

• Example: IQ and SES

  • High SES: IQ mostly explained by genetics (A large, C near 0).

  • Low SES: IQ more influenced by shared environment (C large, A near 0)

→ Interpretation: In deprived environments, environmental inequality matters most; in enriched environments, genetic variation explains more of the remaining differences

Heritability of a trait determines how effectively natural selection can change it

precondition for natural selection to be effective

some heritable genetic variation for the characteristic

evolutionary stable strategy

characteristic or behaviour that , once commen in a population, cannot be out-competed by any alternative behavioural policy

• innovations that enhance the interests of the group at the expense of the individual are UNlikely to be evolutionary stable

• eg. selfishness (not altruism) 

• natural selection will always find the ESS in the end

Intra-genomic conflict

some genes persue their own interests at the expense of the whole

• => cooperation isn’t perfect

Kin selection

= evolutionary mechanism whereby natural selection favours traits that promote the reproductive success of relatives, even if this is at the expense of the individual itself

• idea : helping genetically related individuals indirectly contributes to passing on shared genes to subsequent generations

eusociality

eg. ants, bees, wasps

= a whole colony of individuals work together to further the reproduction of one or just a few of their number

• eusocial colony of a bee or wasp can be viewed as a kind of organism rather than a group of individuals (just as you can be viewed as an organism rather than a coalition of genes)