Question

From an evolutionary perspective, why do humans (and some, but not all other complex eukaryotes) senesce?
Why do they slowly deteriorate with age, rather than staying perfectly healthy until eventually getting
hit by a bus or eaten by a lion? Explain and explore one evolutionary explanation for senescence.

Answer 1

senescence may be cellular aging or senescence of whole organism. here the questionn deals about wenescence of whole organism.

senescence is thought to be evolved due to the reduction in chances of an older organism to live, that may be due to predation or accidents.

Plietropy theory explains that shorter life span with higher reproductive rate at young age results in higher reproductive success that is favored by natural selection. Even ifwe think under the context of natural selection or survival of fittest, the older organisms are relatively incapable of doing many things compared to younger organisms. Therefore the nature eliminates such organisms to maintain the population healthy.

Aging is the important factor that contributes to investment of resources in reproduction rather than maintenance of body for longer periods. According to selection shadow, Deleterious mutations or genetic drift mechanisms accumulate over the age of any organism. Higher accumulation of deleterious mutations are found in older organism that may make the whole population unstable. This is also known as mutation accumulation theory. This theory states that the force of natural selection becomes weak with increasing age and leads to accumulation of mutations in older age.

Pleiotropy is the process where a single gene controls multiple traits. Some of these traits increase fitness at early stages of life but may have negative effects in later stages of life. That means earlier stages have positive effects on fitness whereas older age have negative effects. Positive effects are strongly selected over negative effects by nature.