Final answer:
The fact that human traits vary independently demonstrates why populations are not alike. When populations are geographically separated, their allele frequencies gradually become more different, and different adaptations may be favored by natural selection.
Step-by-step explanation:
The fact that human traits vary independently demonstrates why populations are not alike. This is because populations can become geographically discontinuous, leading to the independent evolution of different traits in each population. When populations are geographically separated for a long period of time, their allele frequencies gradually become more and more different due to new alleles arising by mutation. Additionally, environmental conditions can differ between populations, causing natural selection to favor different adaptations in each group.