The age distribution of human populations is unique among animal species. Children remain dependent on their parents for an extended time, and the elderly live long after the end of their reproductive period. Some scientists now speculate that microorganisms may be responsible for this unusual aspect of human nature. To test this idea, researchers created mathematical models of early hunter-gatherer societies and divided each population into three age groups: juvenile, reproductive, and senescent. They then analyzed how different gut bacteria might influence fertility and mortality rates, and concluded that evolution has favored microbes that preferentially increase death rates in the elderly. By targeting the aging, more resources could be allocated to procreating members of society, improving survivorship and stability of the overall population — especially in the face of environmental challenges, such as famine or virulent disease. While interesting, their modeling efforts lack physical validation, and relies heavily on the assumption that microbes are robustly passed between generations. Although mother-to-infant microbial transmission has been well studied, just how long specific microbes subsist within a maturing human remains unclear.
Acknowledgments: Many thanks to Elizabeth Brown, a graduate student in Human Evolutionary Biology at Harvard University, for her expertise and commentary on the topic.
Managing Editor: Laura L. Smith
Microbiome May Have Shaped Early Human Populations (Phys.Org)
Population Pyramids: Powerful Predictors of the Future (TedEd)