Evolution And Theories Of Ageing Flashcards
What is ageing?
Progressive loss of function accompanied by decreasing fertility and increasing mortality with advancing in age.
When does fertility in women stop?
45-50 years old
Why do women stop being fertile?
We have a finite number of egg cells, eventually we run out of coccyges.
What is the issue with proximate cause of women becoming infertile?
Why wouldn’t natural selection not produced a longer lasting ovary.
Why would the difficulty of birth lead to women becoming infertile later in life?
May be a fitness advantage to limiting reproduction to ages when it is comparatively safe so women can raise existing offspring to independence
Why is the ‘grandmother hypothesis’?
Woman avoid danger of childbirth but benefit as a grandmother to help care for offspring.
Why do we age?
Diversity in longevity betweenspecies show there maybe genes for ageing
Is ageing programmed?
No
How do we know ageing isn’tprogrammed?
- There is no evidence of ageing genes
- Group selection necessary for ageing doesn’t work
- selection is weak at old age
How does extrinsic mortality drive ageing?
Sources of extrinsic mortality imposes a limit on life span
Genes are selected to ensure survival for expected lifespan and no more
What are evolutionary theories of ageing?
- Mutation accumulation
- Antagonistic pleiotropy
- Disposable soma
Who came up with the mutation accumulation theory?
Peter Medawar in 1952
What is the mutation accumulation theory?
Deleterious mutations are selected against at a young age.
Expressed at a later stage of life because you have already passed on your genes.
Selection is weaker later in life.
Why is selection weaker in life?
Extrinsic mortality
Mutation accumulate
What is Huntington’s disease?
Genetically determined (dominant)
Neurological disorder
Severe symptoms
When does Huntington’s disease occur?
40-50 years (after reproduction)
What disease proves the mutation accumulation theory?
Huntington’s disease because it occurs after reproduction.
What is in antagonistic pleiotropy theory of aging?
Mutations that are beneficial early in life (before reproduction) but are deleterious later in life do not get selected out of a population because selection is less efficient later in life.
How is oestrogen an example of antagonistic pleiotropy?
In early life it provides higher fertility but later in life high levels of oestrogen may lead to breast cancer.
Who came up with the antagonistic pleiotropy theory?
George Williams in 1957
What is the evidence for a genetic contribution to ageing?
Comparing longevities of mono- and di-zygotic twins suggest that 25% of variability in ageing is explained by genes.
What is the issue with the evidence for a genetic contribution to ageing?
Some studies suggest only 10% of the variability in longevity is explained by genes.
What is the disposable soma theory?
Ageing is caused by accumulation of damage.
Deprivation orresources
Maintenance vs. Reproduction
What predictions are made in the disposable soma theory?
Multiple types of damage.
Long-lived species should have better defences and accumulates damage more slowly.
