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what did Darwins' ideas contradict?


and Cartesian dualism= Idea that the body and the mind are two separate things- body is subject to biological processes but mind is distinct- but Darwin argued brain is the same as the body and limited by biological processes.


define genetic evolution

a change in (allele frequencies in) the gene pool over successive generations


what cases evolution?

random variation of traits (coded by genes)

forces of selection acting on those traits which are
1) genetic shift (random)
2) selection systematic


what is a gene

– a sequence of DNA that occupies a specific location on a chromosome


what does a gene provide?

– provides the instructions for the assembly of amino acids into proteins


what is an allele?

• An allele is one member of a pair or set of genes that occupy a specific position on a specific chromosome


how can variation arise?

– Recombination in meiosis- variety of maternal and paternal genes hence siblings can be far more and far less related to each other.
– Sexual reproduction
– Mutation (copying error)


what forces of selection are there?

Genetic drift (random) and selection


when does selection occur?

o Occurs when a genetically controlled trait or preference results in differential survival and reproduction by those who possess it versus the people who have a different version of the trait.


what ways can selection work?



what is directional selection? and give an example

-higher (or lower) values increase fitness
-a particular value of that trait is particularly useful and everyone shifts in that direction

e.g. anthropoid brain size


what is stabilizing selection? and give an example

– No fitness advantage to very high or low values; rapidly fluctuating selection pressures so that medium values have best of both worlds
– Keeps everything at one point in the spectrum

e.g. giraffes long necks


what is disruptive selection and give an example

creates two different populations
– No real advantage to a medium so you end up with a population of two subgroups

e..g anisogomy (sperm and egg of males and females are different- far more effort into ovum than sperm creation)
– Small gametes have quantity advantage (carry no nutrients so are cheaper and can make more)
– Large gametes have quality advantage (carry nutrients so more likely to survive/ be viable regardless of size of partner gamete)


what is the different sizes in gametes referred to as?



what two modes of selection did Darwin propose?

1) Natural Selection
2) Sexual Selection


explain natural selection

• Differential reproduction due to differential survival
• (Survival of fittest- not acc coined by Darwin)
• Characteristics which enhance survival are passed into the next generation
• Differential reproduction due to differential survival


give an example of natural selection

The evolution of beak shape in Galapagos medium ground finches (data from Grant & Grant, in Boyd & Silk: How Humans Evolved.)
During drought seasons, seeds on the Galapagos islands become bigger and harder. Ground finches eat these seeds. We know that beak depth is useful for cracking seeds- bigger jaw and more muscle can eat bigger and harder seeds. Post selection (drought) there is more representation and more survival with those with big beaks. Over the period of the drought start of with shallower drought it goes up and then stays up as in 1978 compared to 1975 year before drought those who are around are those who survived/ offpring of those who survived the drought- stays high because gene pool has been changed.


explain sexual selection

• Differential reproduction given survival
• “survival of the prettiest”
• Characteristics which enhance reproductive success are passed into the next generation
• You can live to 80 but if you don’t produce offspring your genes can’t be passed on.
• Many morphological and behavioural differences between males and females are likely to have evolved via sexual selection


what are the two forms of sexual selection

intersexual and intrasexual selection


what is intersexual selection

compete by exhibiting traits that are desirable to the opposite sex


give an example of intersexual selection

- intersexual selection in widowbirds
– Andersson (Nature 1982)
– Females visit male territories, the mail display their tail and the females are attracted.
– Manipulated tail length -tail cut or tail extended with cut off feathers
– Extremely well done, controlled study – control where tails cut off and then put on again- needed because need to check that just having tail messed with alone doesn’t do anything
– Females preferred experimentally longer tails
– This is sexual selection via female choice


what is intrasexual selection

compete by direct contest to establish within-sex dominance or territorial control (e.g. chimps fighting other males)


give an e.g. of intrasexual selection

• Intra-sexual selection in Red-winged blackbirds
– Hanson and Rohwer (1986)
– Males defend territories and attract females to their territory
– However this is probably not due to female choice- females are going to territory and the male is there so they mate with him
– Birds with experimentally blackened epaulets (i.e. not red)
• receive more challenges for their territory (left)
• produce a lessened response when they challenge
• (I.e., they are considered less of a threat). Is not about showing females but is about signaling to other males that you are a threat and they should stay away


what have evolutionary psychologists mainly restricted 'sexual selection' to

to intrasexual or intersexual competition for mating opportunities


what is it important to remember when considering natural and sexual selection?

sometimes natural and sexual selection are in conflict things that help you survive might not help you reproduce and vice versa. When you get this in a situ is important to remember these two things are happening. Can think of sexual selection as a component of natural selection or something that can act in conflict and can be independent.


what is the 'essence' of evolutionary theory?

• In a given ecological niche, certain characteristics will enhance an organism’s ability to survive and/or reproduce within that population/ niche.
• Where a characteristic does enhance survival and reproduction, the genes ‘coding’ for that characteristics will be more likely to be passed on to..
o Children
o Grandchildren
o Great-grandchildren
o Until most of the population have it … or something else gets in the way
o Or until the niche changes and that trait is no longer of use.


what are common misunderstandings about natural selection?

1. Group selection
2. Evolution of complex traits is impossible
3. All evolution is gradual
4. Explaining an immediate cause negates the need for evolution
5. Evolutionary approaches are biologically determinist


what is wrong about group selection?

gene is a unit of selection gene frequency is what’s important doesn’t matter what is happening to individual/ group/ species as long as the gene is going into the next generation.


who suggested an example for group selection but what is the issue here?

Wilson and Sober (1994)

• Have to go quite a long way to come up with an idea about how group selection may work- one one island a genetic mutation produces increased feeding efficiency. Individuals with the gene have higher survival and reproductive success, and over time replace those without the gene. However, the group on the island then outstrips its resources, and goes extinct. In this case, group level characteristics are useful for thinking about natural selection: although selection occurs at the level of genes within individuals, the characteristics of groups can be important determinants of changes in gene frequencies over time (i.e., evolution).”


What does group selection require? And what does this mean?

• Group isolation – so no genetic exchange with other groups
• Rapid group extension – so can’t adapt to circumstances
• Very strong selection- acting on some groups and not others
Hence this is so rare especially in humans where we can see genomes travel huge distances so doesn’t really apply to humans.