Eastman Charmane I, Tomaka Victoria A, Crowley Stephanie J
Biological Rhythms Research Laboratory, Behavioural Sciences Department, Rush University Medical Center, Chicago, IL, USA.
J Sleep Res. 2017 Oct;26(5):547-550. doi: 10.1111/jsr.12521. Epub 2017 Mar 23.
The endogenous, free-running circadian period (τ) determines the phase relationship that an organism assumes when entrained to the 24-h day. We found a shorter circadian period in African Americans compared to non-Hispanic European Americans (24.07 versus 24.33 h). We speculate that a short circadian period, closer to 24 h, was advantageous to humans living around the equator, but when humans migrated North out of Africa, where the photoperiod changes with seasons, natural selection favoured people with longer circadian periods. Recently, in evolutionary terms, immigrants came from Europe and Africa to America ('the New World'). The Europeans were descendents of people who had lived in Europe for thousands of years with changing photoperiods (and presumably longer periods), whereas Africans had ancestors who had always lived around the equator (with shorter periods). It may have been advantageous to have a longer circadian period while living in Europe early in the evolution of humans. In our modern world, however, it is better to have a shorter period, because it helps make our circadian rhythms earlier, which is adaptive in our early-bird-dominated society. European American women had a shorter circadian period than men (24.24 versus 24.41), but there was no sex difference in African Americans (24.07 for both men and women). We speculate that selection pressures in Europe made men develop a slightly longer period than women to help them track dawn which could be useful for hunters, but less important for women as gatherers.
内源性的、自由运行的昼夜节律周期（τ）决定了生物体在被调整到24小时一天时所呈现的相位关系。我们发现非裔美国人的昼夜节律周期比非西班牙裔欧洲裔美国人短（24.07小时对24.33小时）。我们推测，更接近24小时的短昼夜节律周期，对生活在赤道附近的人类是有利的，但当人类从非洲向北迁移时，那里的光周期随季节变化，自然选择青睐昼夜节律周期更长的人。最近，从进化角度来看，移民从欧洲和非洲来到美洲（“新大陆”）。欧洲人是数千年来生活在欧洲、经历光周期变化（可能周期更长）的人的后代，而非洲人的祖先一直生活在赤道附近（周期较短）。在人类进化早期生活在欧洲时，拥有较长的昼夜节律周期可能是有利的。然而，在我们现代社会，拥有较短的周期更好，因为这有助于使我们的昼夜节律更早，这在我们以早起者为主导的社会中是适应性的。欧洲裔美国女性的昼夜节律周期比男性短（24.24小时对24.41小时），但非裔美国人中没有性别差异（男性和女性均为24.07小时）。我们推测，欧洲的选择压力使男性的周期比女性略长，以帮助他们追踪黎明，这对猎人可能有用，但对作为采集者的女性来说不那么重要。
