Evolution of ageing

Question 1

What is the inevitability theory of ageing?

Answer 1

Ageing is inevitable, it didn’t evolve, it just happens.

Question 2

How do we know the inevitability theory of ageing isn’t correct?

Answer 2

Some animals don’t age - urticina felina and hydras

Question 3

What is the mutation accumulation theory?

Answer 3

After Haldane’s observations and thoughts on Huntington’s (the later the effect of the mutation, the weaker the force of natural selection against it), Medawar stated mutations with late life deleteroius effects will accumulate in population causing ageing.

Fewer bearers survive to express later-acting mutations because of the impact of extrinsic hazard, and the force of natural selection against them therefore declines with age. These late-acting mutations can therefore reach a higher frequency under mutation-selection balance. Under this theory, ageing is evolving as a side-effect of mutation pressure

Question 4

What did the trade-off/pleitropy suggest?

Answer 4

Suppose there are mutations are beneficial in youth, but at the price of a higher rate of ageing. More individuals will survive to express the early beneficial effect than will survive to suffer the later higher rate of ageing, because of the impact of extrinsic hazard. Mutations like this can therefore be incorporated by natural selection. This is the pleiotropy (means a single mutation with more than one phenotypic effect) or trade-off theory. Here ageing is evolving as a side-effect of natural selection in favour of mutations that cause a benefit during youth

Question 5

What is the difference between the mutation accumulation theory and the trade off theory of ageing?

Answer 5

Mutation accumulation would imply that we can slow down ageing without affecting events earlier in life, while trade-off theory suggests that a lowered rate of agein could be achieved only at the expense of fitness of youth.

Question 6

What are the 3 predictions and do experiments in drosophila support mutation accumulation theory?

Answer 6

1. Relatives should resemble each other for traits related to fitness more when they are old than young. Experiments don’t support this.
2. Must be late age specific mutations.
3. Walls of death after post-reproductive age but we don’t

Question 7

What is another early evolutionary theory?

Answer 7

Ageing is an adaption. It is for the good of the species - removes worn out individuals so reduces competition for limited resources.

Question 8

How do we know ageing isn’t an adaption?

Answer 8

Test against modern evolutionary theory which is based on selection of traits. It doesn’t work.