Ontogeny

Ontogeny refers to the development of an individual from life to death. The study of ontogeny is also known as life history theory or the cycle of life, which describes the stages of growth and reproduction within one’s lifespan.

Within the animal kingdom, there is extreme diversity between life histories of different species. However, no animal grows and reproduces at the same time. The reproductive period can only begin after growth ends.

Key Events in a Life Cycle #

• Birth
• Childhood
• Maturation
• Reproduction
• Senescence

Key Traits in a Life Cycle #

• Size at birth
• Growth pattern
• Age and size at first reproductive event
• Semelparous (single reproductive event) vs iteroparous (multiple reproductive events)
• Number, size, sex ratio of offspring
• Reproductive lifespan
• Length of lifespan

Key Traits specific to humans #

1. Long lifespan
2. Support of reproduction by older post-reproductive individuals (grandparent effect)
   1. “it takes a village to raise a child” - active teaching by caregivers vs. individual learning in other species
3. Male support of reproduction
   1. Most other apes stay with mother, compared to 50% of childcare being done by mothers in human communities. Other apes often don’t meet or recognize their fathers
4. Extended period of juvenile dependence
   1. Humans take 8 years on average to fully develop brain, compared to 3 for other apes
   2. Don’t start getting own food until mid-adolescence
5. Short inter-birth interval
   1. 3 years between births on average - allows population to grow quickly