Table 1.

Primary hypotheses for the evolutionary basis of ontogenescence.

hypothesis name	hypothesis: death rate decreases with age in developing cohorts because…
quality control hypothesis	… kin terminate potentially inviable individuals early so as to avoid bearing unnecessary costs.
growth trade-off hypothesis	… as individuals grow, they can decrease their relative need for continued growth and therefore accept fewer growth-enabling mortality risks.
robustness hypothesis	… as individuals develop, they acquire characteristics that increase their robustness to insults.
heterogeneous frailty hypothesis	… the frailest individuals die first, causing mean frailty to decline with age.
transitional timing hypothesis	… transcriptional, developmental and environmental transitions are dangerous, and these are concentrated early in life.