Q47 - Williams' Evolutionary Theory of Senescence
Organismal senescence is the aging of the whole organism. It is a widespread phenomenon in nature but the exact etiology is still largely unclear. An evolutionary theory was proposed by George C. Williams which involves the following assumptions:
- Soma (referring to all somatic cells in the body) is essential for reproductive success, but it does not pass on to the offspring.
- Alleles are affected by Natural selection.
- Pleiotropic genes can have opposite effects on fitness at different ages or somatic environments.
- The probability of reproduction decreases with increasing age. Williams suggested the following example: Perhaps a gene was selected for because it codes for calcium deposition in bones, which promotes juvenile survival, but the same gene promotes calcium deposition in arteries.
Using the information and data, determine which of the statements are true or which are false.
A. Lower adult death rates can be associated with lower rates of senescence, according to the theory.
B. Where there is a sex difference, the sex with higher rate of decrease in fecundity after maturation (but with equal death rate to the other sex) should undergo the more rapid senescence, according to the theory.
C. The frequencies of an allele in a gene that behaves similar to the aforementioned calcium deposition gene in a cohort will be smallest at early age and greatest at late age.
D. This model views senescence as an adaptation.
Question reproduced from IBO 2018, Theoretical Paper 1, licensed under CC BY-NC-SA 4.0 - attributed to the International Biology Olympiad. Open the full exam PDF · Community solutions (unofficial)