Extant humans are currently increasing their genetic load, which is informing present and future human microevolution. This has been a gradual process that has been rising over the last centuries as a consequence of improved sanitation, nutritional improvements, advancements in microbiology and medical interventions, which have relaxed natural selection. Moreover, a reduction in infant and child mortality and changing societal attitudes towards fertility have led to a decrease in total fertility rates (TFRs) since the 19thcentury. Generally speaking, decreases in differential fertility and mortality have meant that there is less opportunity for natural selection to eliminate deleterious mutations from the human gene pool. It has been argued that the average human may carry ~250–300 mutations that are mostly deleterious, as well as several hundred less-deleterious variants. These deleterious alleles in extant humans mean that our fitness is being constrained. While such alleles are viewed as reducing human fitness, they may also have had an adaptive function in the past, such as assisting in genetic complexity, sexual recombination and diploidy. Saying this, our current knowledge on these fitness compromising alleles is still lacking.

中文翻译：

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现存人类的遗传负荷和生物学变化

现存人类目前正在增加他们的遗传负荷，这为现在和未来的人类微进化提供了信息。这是一个渐进的过程，在过去的几个世纪里，由于卫生条件的改善、营养的改善、微生物学的进步和医学干预的进步，自然选择放松了。此外，自 19th世纪。一般来说，不同生育率和死亡率的降低意味着自然选择从人类基因库中消除有害突变的机会减少。有人认为，普通人可能携带约 250-300 个突变，这些突变大多是有害的，以及数百个不那么有害的变异。现存人类中的这些有害等位基因意味着我们的健康受到限制。虽然这些等位基因被认为会降低人类健康，但它们过去可能也具有适应性功能，例如协助遗传复杂性、性重组和二倍体。话虽如此，我们目前对这些影响健康的等位基因仍然缺乏了解。