Bronson F H
Department of Zoology, University of Texas, Austin 78712, USA.
Q Rev Biol. 1995 Jun;70(2):141-64. doi: 10.1086/418980.
Almost all human populations exhibit seasonal variation in births, owing mostly to seasonal variation in the frequency of conception. This review focuses on the degree to which environmental factors like nutrition, temperature and photoperiod contribute to these seasonal patterns by acting directly on the reproductive axis. The reproductive strategy of humans is basically that of the apes: Humans have the capacity to reproduce continuously, albeit slowly, unless inhibited by environmental influences. Two, and perhaps three, environmental factors probably act routinely as seasonal inhibitors in some human populations. First, it seems likely that ovulation is regulated seasonally in populations experiencing seasonal variation in food availability. More specifically, it seems likely that inadequate food intake or the increased energy expenditure required to obtain food, or both, can delay menarche, suppress the frequency of ovulation in the nonlactating adult, and prolong lactational amenorrhea in these populations on a seasonal basis. This action is most easily seen in tropical subsistence societies where food availability often varies greatly owing to seasonal variation in rainfall; hence births in these populations often correlate with rainfall. Second, it seems likely that seasonally high temperatures suppress spermatogenesis enough to influence the incidence of fertilization in hotter latitudes, but possibly only in males wearing clothing that diminishes scrotal cooling. Since most of our knowledge about this phenomenon comes from temperate latitudes, the sensitivity of spermatogenesis in both human and nonhuman primates to heat in the tropics needs further study. It is quite possible that high temperatures suppress ovulation and early embryo survival seasonally in some of these same populations. Since we know less than desired about the effect of heat stress on ovulation and early pregnancy in nonhuman mammals, and nothing at all about it in humans or any of the other primates, this is an important area for future research. Third, correlational data suggest that there may be some degree of regulation of reproduction by photoperiod in humans at middle to higher latitudes. Populations at these latitudes often show a peak in presumed conceptions associated with the vernal equinox. On the other hand, evidence gathered by neuroendocrinologists tends to argue against reproductive photoresponsiveness in humans.
几乎所有人类群体的出生都呈现季节性变化，这主要归因于受孕频率的季节性变化。本综述聚焦于营养、温度和光周期等环境因素通过直接作用于生殖轴对这些季节性模式的影响程度。人类的生殖策略基本上与猿类相同：人类有持续繁殖的能力，尽管速度缓慢，除非受到环境影响的抑制。在某些人类群体中，可能有两个甚至三个环境因素通常作为季节性抑制因素起作用。首先，在食物供应存在季节性变化的人群中，排卵似乎受季节调节。更具体地说，食物摄入不足或获取食物所需的能量消耗增加，或两者兼而有之，可能会延迟月经初潮，抑制非哺乳期成年人的排卵频率，并在这些人群中季节性地延长哺乳期闭经。这种作用在热带自给自足社会中最为明显，在那里，由于降雨的季节性变化，食物供应往往差异很大；因此，这些人群的出生往往与降雨相关。其次，季节性高温似乎足以抑制精子发生，从而影响较炎热纬度地区的受精率，但可能只对穿着减少阴囊散热衣物的男性有影响。由于我们对这一现象的了解大多来自温带地区，人类和非人类灵长类动物精子发生在热带地区对高温的敏感性需要进一步研究。在某些相同人群中，高温很可能季节性地抑制排卵和早期胚胎存活。由于我们对热应激对非人类哺乳动物排卵和早期妊娠的影响了解不足，对人类或其他灵长类动物更是一无所知，这是未来研究的一个重要领域。第三，相关数据表明，在中高纬度地区，光周期可能对人类生殖有一定程度的调节作用。这些纬度地区的人群通常在与春分相关的假定受孕方面出现高峰。另一方面，神经内分泌学家收集的证据往往反对人类存在生殖光反应性。
