文明的纠结-朋友之间拥有相似的基因组？

  最近美国科学院院刊（PNAS)发表了一篇文章，该文比较了朋友之间和陌生人之间的SNP相似度，研究者发现朋友之间基因组内的SNP享有0.1%的相似度，不同于陌生人之间。这大约相当于中国“五服”之内的SNP相似度。

注：五服，是指从自己算起至自己的爷爷和自己的孙子，如果按照西方的算法，应该是自己儿子的儿子的儿子的儿子，即重孙子的孩子们之间具有的SNP相似度。

     http://www.pnas.org/content/early/2014/07/10/1400825111

More than any other species, humans form social ties to individuals who are neither kin nor mates, and these ties tend to be with similar people. Here, we show that this similarity extends to genotypes. Across the whole genome, friends’ genotypes at the single nucleotide polymorphism level tend to be positively correlated (homophilic). In fact, the increase in similarity relative to strangers is at the level of fourth cousins. However, certain genotypes are also negatively correlated (heterophilic) in friends. And the degree of correlation in genotypes can be used to create a “friendship score” that predicts the existence of friendship ties in a hold-out sample. A focused gene set analysis indicates that some of the overall correlation in genotypes can be explained by specific systems; for example, an olfactory gene set is homophilic and an immune system gene set is heterophilic, suggesting that these systems may play a role in the formation or maintenance of friendship ties. Friends may be a kind of “functional kin.” Finally, homophilic genotypes exhibit significantly higher measures of positive selection, suggesting that, on average, they may yield a synergistic fitness advantage that has been helping to drive recent human evolution.

 这篇文章所得出的结论引发巨大争议。很多人指出研究者局限在一个小城居民不妥。

这确实是个问题。

但除此之外，研究者所得出的结论也不符合逻辑。假如研究者的结论是合理的，那么你应该期待“夫妻”之间的基因组会更相似，而夫妻之间生育的子女会明显趋向于降低等位基因的遗传多样性。而这不利于其子女适应环境，与进化论的观点是相悖的。