Our Tangled Family Tree

Consider Homo naledi.  A humanoid species whose remains were found several years ago in a cave in South Africa, it had a smaller brain than our direct ancestors, walked upright, and may have used tools.  And, scientists now believe, it lived between 236,000 and 335,000 years ago — which means it would have been alive and kicking when early humans were, too.

mm8345_20150306_134-3The dating of the remains of Homo naledi suggests that the family tree of human beings is a lot more tangled than people once thought.  As scientists focus more and more on searching for fossil evidence of human-like species, they are uncovering new information that reveals a number of different species romping around the pre-historic world.  The Smithsonian page on human ancestry now shows more than 15 early human species.  With so many variations of humanoids, there are bound to be evolutionary dead ends — and, the more human-like remains that are found, the more likely it is that the different offshoots of the evolutionary tree overlapped in time and may have interacted.

Scientists already believe that, around 300,000 or so years ago — or about the same time as the dates suggested for Homo naledi — there were three different offshoots of one of the root humanoid ancestors, Homo heidelbergensis.  Humans remained in Africa, Neanderthals ventured from Africa into Europe, and Denisovans moved east, into Asia.  We know that, for many years thereafter, there was physical interaction between human ancestors and Neanderthals, because many modern humans have a small percentage of Neanderthal DNA.  With three groups of humanoids around, it’s not much of a stretch to imagine Homo naledi existing in that same time frame.   And who knows whether scientists will unearth evidence of other distinct, humanoid species that also date from that same time period?

The intriguing question is:  what happened to those other species?  Did the human ancestors simply prove to be superior in brainpower, body design, tool-making ability, and other attributes that gave them an evolutionary advantage and allowed them to simply out-compete the other species for food, living space, and other conditions that made humans more successful in reproducing . . . or did the early humans slaughter those who were different and drive them into extinction?  Maybe there is a reason that the remains of Homo naledi were found in a cave — they were desperately hiding from our ancestors.

Species-Saving Sex

Don’t look now, but the history of homo sapiens — and of human-like creatures on planet Earth — is getting progressively weirder and more titillating.

article-2029559-0d8dcb7300000578-310_1024x615_largeScientists conducting studies of human genes are learning lots of interesting information about the development of our species.  One of the more provocative findings is that our genetic information indicates that there were multiple instances of significant homo sapien interbreeding with other human-like species — specifically, the Neanderthals, and a mysterious, largely unknown species called the Denisovans —  that left indelible marks in the DNA of modern humans.  And it also appears that the cross-breeding provided us with some useful genetic material, including genes that enhanced the operation of the human immune system and helped our ancestors fight off pathogens.

Not much is known about human history before the dawn of civilization.  Most of what we understand comes from looking at fossils of human ancestors and attempting to piece together the gnarled branches of the human family tree.  Human genetic analysis provides a different kind of window to the past of our species.  It’s now obvious that the early days of the human species saw our ancestors competing with — and apparently having lots of sex with — other hominid species.  We couldn’t have been too much different from them, because the genome evidence means that when humans had sex with Neanderthals and those enigmatic Denisovans, their one-night stands produced pregnancies and non-sterile offspring that, in turn, shared their genes through mating.  All of that cross-breeding among different species helped to make humans what they are today.

We might never learn what happened to the Neanderthals, or the enigmatic Denisovans, and why they died out while humans survived and became the dominant species on the planet.  What we can now say with some confidence is that human ancestors apparently were as interested in sex as modern humans are, and weren’t particularly troubled about who — or what species — they were having sex with, either.