Timescales of human adaptation: the role of epigenetic processes.

Human biology includes multiple adaptive mechanisms that allow adjustment to varying timescales of environmental change. Sensitive or critical periods in early development allow for the transfer of environmental information between generations, which helps an organism track gradual environmental change. There is growing evidence that offspring biology is responsive to experiences encoded in maternal biology and her epigenome as signaled through the transfer of nutrients and hormones across the placenta and via breast milk. Principles of evolutionary and comparative biology lead to the expectation that transient fluctuations in early experience should have greater long-term impacts in small, short-lived species compared with large, long-lived species such as humans. This implies greater buffering of the negative effects of early-life stress in humans, but also a reduced sensitivity to short-term interventions that aim to improve long-term health outcomes. Taking the timescales of adaptation seriously will allow the design of interventions that emulate long-term environmental change and thereby coax the developing human body into committing to a changed long-term strategy, yielding lasting improvements in human health and wellbeing.