Human beings are a lot more diverse than you first thought.
It turns out that some hybrid species are more vigorous and better-suited to their environment than their speciated parents. They are not all mules. For example, the European bison is a successful hybrid arising from a steppe bison and an auroch, both now extinct. The human race has benefitted from hybridisation too. We have all heard that humans other than those from sub-Saharan African have some Neanderthal DNA in them. The benefits extend to hair, skin and disease resistance. Many people in the Far East have Denisovan DNA in them. One of the benefits from that hybridisation is the ability for Tibetans to live comfortably at high altitudes. Some sub-Saharan Africans carry DNA from ancient species that have not so far even been identified.
You may also like to browse other evolution posts: https://www.thesentientrobot.com/category/evolution/