Convoluted human evolution: a branch is missing (Introduction)

by David Turell , Friday, July 28, 2017, 19:35 (2675 days ago) @ David Turell

No fossils found but a compound in human saliva says someone is missing:

http://bigthink.com/philip-perry/researchers-found-evidence-of-a-human-ancestor-weve-ne...

"We know that humans, Neanderthals, and Denisovans had a common ancestor named Homo heidelbergensis, who lived 700,000 to 200,000 years ago. H. heidelbergensis had a short, wide body which preserved heat. As such, it was the first hominin who was able to live in colder climates.

"H. heidelbergensis was no slouch. It used spears for hunting and had fire. It was also the first to make shelters out of rocks or stones, and the first to hunt large game. Somewhere around 300,000 to 400,000 years ago, a group of them migrated out of Africa. Sometime after that, it split off into Neanderthals and Denisovans. While Neanderthals settled in Europe and Western Asia, Denisovans migrated to central and Southeast Asia, traveling as far as the Pacific Islands and even Australia.

"Somewhere around 130,000 years ago our ancestors, Homo sapiens, came onto the scene. Although, new evidence may push their arrival much farther back, to 300,000 years ago, according to a newly discovered skull, excavated from a cave in Morocco last June. Supposedly, humans didn’t start migrating out of Africa in large numbers until 125,000-60,000 years ago. Some scholars believe a smaller, earlier migration took place before the larger one.  

***

"Now a team of experts, led by two professors at the University of Buffalo, report findings that fragment our understanding even further. They’ve isolated a gene from an ancient hominin species we’ve never encountered before. It’s some kind of genetic missing link. The gene known as MUC7 is present in the saliva of all humans. But it’s radically different from one lineage to the next.

***

“'Our research traced the evolution of an important mucin protein called MUC7 that is found in saliva,” he said. “When we looked at the history of the gene that codes for the protein, we see the signature of archaic admixture in modern day Sub-Saharan African populations.”

"MUC7 is the gene which produces mucin, the substance that makes saliva thick and sticky. As such, it binds to microbes in an effort to protect the body from infection.  Not all of the MUC7 genes are the same, however. It is these variations which can help scientists untangle the different strains leading to different lineages.

"Researchers examined MUC7 within the genomes of 2,500 participants. Those from Sub-Saharan Africa had a type that varied considerably from those from other regions. The gene was so different in fact, Neanderthal and Denisovan genomes were more closely aligned with ours more than this variety. The evolutionary path of us and this “ghost” ancestor split 500,000 to 2.5 million years ago. Our ancestors are thought to have admixed with them somewhere between 200,000 and 150,000 years ago.

"Dr. Gokcumen said:

"Based on our analysis, the most plausible explanation for this extreme variation is archaic introgression — the introduction of genetic material from a ‘ghost’ species of ancient hominins. This unknown human relative could be a species that has been discovered, such as a subspecies of Homo erectus, or an undiscovered hominin. We call it a ‘ghost’ species because we don’t have the fossils."

Comment: Like the Denisovans about whom we only have a tooth and a little finger, in this case we have genetics but no bones. H. naledi bones (15 individuals) were just discovered. How many other branches are yet to be found. There appears to be a large bush of hominins, when nothing else advanced. Looks like a purposeful push toward H. sapiens.