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Human Interbirth Patterns

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The lives of humans and chimpanzees are controlled by life history. Their bodies decide when to provide energy for growth, repair, or reproduction. These decisions are most obvious in females who show the switch from growth to reproduction with menarche, and the end of the reproductive phase with menopause. Life history also involves looking at the time females take between the birth of each of their children and what happens after women stop reproducing. One way to get a good understanding of the long life history of chimpanzees and humans is to compare them and see how their life histories correlate in areas like becoming reproductively active, their interbirth intervals, and their post-reproductive phase.
The age at which female humans …show more content…

The Mahale chimpanzees were found to have a median interbirth interval of 68 months if the last offspring was a male and 66 months if the previous offspring was female (Nishida et al.). This rounds out to be about 5 ½ years between births. Human birth intervals are variable across cultures and socioeconomic statuses but, "Present day populations exhibiting natural fertility have a typical interbirth interval in the range of 3–5 years" (Thomas et al.). This is shown in groups like the !Kung San, hunter gatherers who live in Botswana and have 4 year birth intervals (Cartwright, 71). Other Sans people who lived in different local environments also had an optimal interbirth interval of about 4 years and the Ache hunter gatherers of Paraguay have a median interbirth interval of about 3 years (Thomas et al.). Human interbirth intervals are much shorter in rural/premodern societies where food resources are more abundant but where options like reliable contraceptives are not yet available (Cartwright, 73). Modern/Urban societies that do give women access to contraceptives allow women to decide the best interbirth interval for themselves. One reason that chimpanzees may have a slightly higher interbirth interval is that human babies are weaned earlier allowing the mothers to be more fertile (Thomas et al.). This however probably requires the mother to have a support networks of other humans willing to help raise her children. These would be expected to be kin and this might be one of the factor that leads to women staying alive long enough to become

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