When we speak simply of evolution there are two basic types. The first is macro-evolution which is what most people are acquainted with. That is, the theory that man evolved from lower species to higher species such as in the case of H. erectus evolving into early modern man (Cro-magnon). But there is another evolutionary theory that speaks of micro-evolution.
Micro-evolution is a horizontal model of human evolution rather than a vertical one such as macro-evolution. An example of microevolution is dog breeding. We breed different breeds or species of dogs to get the qualities we want. Under this theory the same principle applies to human evolution.
Microevolution holds that there were different species (breeds) of ancient humans such as H. erectus, H. habilis, H. ergaster, etc. The idea is that modern humans, Homo sapiens, did not evolve from anything. Rather, the various species of humans interbred and the result was hybrid modern humans, US!
Microevolution explains much about human evolution and under this theory there are no “missing links” while macro-evolution has many such “missing links” (transitional species). There are no missing links (transitional forms) because we didn’t evolve from anything but, rather, we interbred with different species (breeds) of humans.
This is why we can look at modern humans, Homo sapiens, and see various traits from other species of humans such as Neanderthals and Homo erectus! Some of our ancient ancestors interbred more with one human species than others. For example, we see very distinct Neanderthal traits in some modern humans while in others we see no Neanderthal traits at all. The same with Homo erectus. In some modern humans we see clear erectine traits such as remnants of a sagittal crest atop the head and even perhaps a somewhat more pronounced browridge! We might also see in some humans with more prognathism in the face (meaning their lower face protrudes outward) such as we find in Homo habilis, “Handyman.”
This also explains some atavism we encounter in people including newborns such as a modern human child born with excessive body hair, prognathism, a tail, etc. All of these oddities, microevolution holds, are not the result of vertical evolution (macro-evolution) but are the result of various ancient human species (breeds) interbreeding with one another.
Occam’s Razor, also known as Ockham’s Razor, is a problem solving principle from philosophy that, simply, holds that when two or more theories are presented the one with the LEAST assumptions should be chosen as it is most likely the correct theory. When it comes to human evolution and the two models I’ve presented here Microevolution is the theory with the least assumptions while macro-evolution is the one with the most assumptions. Thus, using the principle of Ockham’s Razor, Microevolution would be the most correct theory when it comes to human evolution!
It is the microevolution model that I adhere to as it explains far more about modern human origins than does the macro model. To me the interbreeding of different species of ancient humans is evident by just looking at modern humans, Homo sapiens. We are all Homo sapiens but we did not all evolve from the same ancient species of humans. Rather, we are the products of the interbreeding between various species (breeds) of ancient humans (hybrids). Some of our ancestors interbred more with, say, Homo erectus while others preferred to interbreed with Neanderthals and that is why we see some ancient human traits in modern humans from one ancient human species in some more than others. So, we modern humans arrived via interbreeding as HYBRIDS. We didn’t evolve from anything! Human evolution is a horizontal line or twisted vine and NOT a vertical line or ladder. Ancient human ancestors didn’t go extinct. They were assimilated into new human species via human species interbreeding. And this microevolution model also explains why we find anomalies such as why later Homo erectus appears more archaic that earlier Homo erectus et al. In the case of this anomaly with H. erectus it’s not a matter of evolution nor is it a mystery. In fact, later H. erectus appears more archaic than earlier H. erectus due to retrobreeding (back-breeding) which also occurred.