It's weird to think that tens of thousands of years ago, humans were mating with different species—but they were. That's what DNA analyses tell us. When the Neanderthal genome was sequenced in 2010, it showed that as much as 1 to 4 percent of the DNA of non-Africans might have been inherited from Neanderthals.
LiveScience: The earliest known ancestors of modern humans might have reproduced with early chimpanzees to create a hybrid species, a new genetic analysis suggests. The earliest known ancestors of modern humans might have reproduced with early chimpanzees to create a hybrid species, a new genetic analysis suggests.
Their genomes are simply too different to come together and make something that will live. Their genomes cannot mix in any productive way.
As some of the first bands of modern humans moved out of Africa, they met and mated with Neandertals about 100,000 years ago—perhaps in the fertile Nile Valley, along the coastal hills of the Middle East, or in the once-verdant Arabian Peninsula.
The biological species concept
Thus all living Homo sapiens have the potential to breed with each other, but could not successfully interbreed with gorillas or chimpanzees, our closest living relatives. On this basis, 'species' that interbreed with each other cannot actually be distinct species.
It's thought that at one time, human ancestors did engage in chimp-like habits of sex and child-rearing, in which strong alpha males mated freely with the females of their choice, and then left the child-raising duties to them.
An ancient child from Siberia is believed to be the only know individual whose parents were from two different species. The studied remains belonged to a girl who had a Neanderthal mother and a Denisovan father.
In doing so, they found evidence that Homo sapiens not only had sex with Neanderthals, they also interbred with Homo erectus, the "upright walking man," Homo habilis, the "tool-using man," and possibly others.
While the new study confirms that modern humans interbred at least three times with ancient hominins—once with Neanderthals, and twice with the Denisovans—it also raises the possibility of even more extensive intermixing on the part of our ancient ancestors.
For humans, monogamy is not biologically ordained. According to evolutionary psychologist David M. Buss of the University of Texas at Austin, humans are in general innately inclined toward nonmonogamy.
No baby is born in such circumstances. It is impossible for one species to impregnate a member of another species. Good thing too, or we'd have alligators breeding with elephants.
In fact, such human-animal hybrids are often referred to as “chimeras”.
Cross-species fertilization: the hamster egg receptor, Juno, binds the human sperm ligand, Izumo1 - PMC.
Impregnation: Impregnation is actually the fertilization process in which sperm and ovum fuse to produce a zygote. Naturally, a human cannot impregnate a pig as there are many reproduction barriers between them.
Summary: Male physical competition, not attraction, was central in winning mates among human ancestors, according to an anthropologist in a new study. Male physical competition, not attraction, was central in winning mates among human ancestors, according to a Penn State anthropologist.
Broadly speaking, evolution simply means the gradual change in the genetics of a population over time. From that standpoint, human beings are constantly evolving and will continue to do so long as we continue to successfully reproduce.
With fewer Neanderthals breeding with each other and group sizes already small and scattered due to the environment, hybridisation outside of Neanderthal family groups could have helped push the species into decline.
To this day, there are people carrying genetic material from at least two different populations of Neanderthals, which one analysis suggests interbred with humans several times in both Europe and Asia. Read about the ancient teeth found in Jersey that show signs of interbreeding between Neanderthals and modern humans.
Roughly two percent of the genomes of Europeans and Asians are Neanderthal. Asians also carry additional Denisovan DNA, up to 6 percent in Melanesians. But African populations seemed to have largely been left out of this genetic shakeup.
Homo erectus characteristics
H. erectus is the oldest known species to have a human-like body, with relatively elongated legs and shorter arms in comparison to its torso. It had an upright posture.
The most recent fossil and archaeological evidence of Neanderthals is from about 40,000 years ago in Europe. After that point they appear to have gone physically extinct, although part of them lives on in the DNA of humans alive today.
This analysis suggested that Denisovans, much like Neanderthals, had a long, broad, and projecting face; large nose; sloping forehead; protruding jaw; elongated and flattened skull; and wide chest and hips. The Denisovan tooth row was longer than that of Neanderthals and anatomically modern humans.
Holarctic ravens and Californian ravens had been two separate species for 1.5 million years until tens of thousands of years ago when their regions overlapped and they began to merge into a new species. This new raven species contains genes coming from both the Holarctic and Californian raven.
Broadly speaking, different species are unable to interbreed and produce healthy, fertile offspring due to barriers called mechanisms of reproductive isolation. These barriers can be split into two categories based on when they act: prezygotic and postzygotic.
The results suggest that people deliberately sought partners beyond their immediate family, and that they were probably connected to a wider network of groups from within which mates were chosen, in order to avoid becoming inbred.