As it became possible to analyze an individual’s genetic makeup, it become apparent that there was much more variation within populations than prevailing evolutionary theory predicted. Indeed, individuals could have similar traits but very different gene sequences.
脱氧核糖核酸（DNA）的发现挑战了上述观点的可信性。因为现在可以对个人基因组成进行分析，人们逐渐了解到种群中存在的基因变异比主流进化论所做的预测要多得多。事实上，类似特征的人可以有完全不同的基因序列。而这显然违背了所谓的自然选择法则。