Photo credit: M. GardeFerdinand (CC BY-SA 3.0)
We all know how AMHs (Anatomically Modern Humans) evolved, right? We have all seen the picture… A string of small, hunched over, knuckle dragging monkeys gradually stood more upright until they blossomed into the magnificent specimens that one might see standing behind the counter at any McDonalds in the modern era. At one point around 60,000 years ago, a small, tightly knit family of these spear holding AMHs made the brave decision to leave East Africa and venture into the beyond; to the Middle-East and Europe. Over time they spread to every corner of the Earth, with different populations evolving new traits such as the ability to metabolise alcohol and digest animal milk. Well, sorry to disappoint but this is bollocks.
For starters, the familiar cartoon entitled “The Road to Homo Sapiens”, embodies the now discredited “March of Progress” theory which postulated that evolution is a progressive process. It isn’t. In fairness though, it was originally designed for publication in the 1965 work: the Early Man volume of the Life Nature Library, by F. Clark Howell, who explicitly explained that the evolution of mankind probably wasn’t a progressive process. The image was designed merely to get the reader’s noggin a-jogging. As the old saying goes though, a picture can say a thousand words and because of its substantial emotive power, “The Road to Homo Sapiens” became a meme almost instantly. We have all seen the parodies, millions of years of evolution having culminated in a slouching Homer Simpson. Indeed, the brilliant evolutionary biologist Steven Jay Gould, in his book “Wonderful Life” explained:
“The march of progress is the canonical representation of evolution – the one picture [“The Road to Homo Sapiens”] immediately grasped and viscerally understood by all. … The straitjacket of linear advance goes beyond iconography to the definition of evolution: the word itself becomes a synonym for progress. … [But] life is a copiously branching bush, continually pruned by the grim reaper of extinction, not a ladder of predictable progress”.
Unfortunately, the quibbles with this image do not end there, oh no. There are things other than the implied progressive nature of evolution that are wrong with the schematic representation. Chiefly amongst these is that humans did not evolve from Chimpanzees! Or anything like them for that matter.
Let’s back up for a moment. As Stephen Jay-Gould said, the process of evolution does not produce a straight line of organisms but a copiously branching bush. This is a vital point. Any Turtle fossil that a palaeontologist finds almost certainly did not produce offspring that in turn produced offspring that eventually formed a long line that producing modern day turtles. No. In fact, these fossilised turtles form branches on a tree. These fossilised specimens are probably slightly different from the actual ancestors of modern-day turtles. This is the same with human ancestors!
Human beings are part of a group of primates known as the Great Apes or “Hominids”. The Hominids include four genuses: Pan, containing the Chimpanzees; Pongo, containing the Orangutans; Gorilla, containing the Gorillas and Homo. AMHs (us) have the species name sapiens; Homo is the name of our genus. Hominin is the term applied to any member of the genus Homo.
It is vital to understand that at some point in history, all these four genuses shared one common ancestor. This ancestor then gave rise to a long lineage which was subject to evolution and diversified into many subsequent groups: some of these groups went extinct long ago! These four genuses are the ones that have survived over time. miRNA studies have suggested that the first extant (group that still exists) genus to split off from the common ancestor was pan with the next to split off being Gorilla. The current genetics literature cites data that show Homo is most closely related to Pan. There was a common ancestor of Pan and Homo, but these two groups eventually split apart. There are many extinct species of Homo and (remember the turtles) most of these Hominins are branches on the tree; not directly related to sapiens through unbroken lineage. These branches produced many familiar species such as the Homo neanderthalensis, Homo erectus and Homo heidelbergensis. It should be clear that we did not evolve from Chimpanzees.
Now, scientifically speaking, we could give Rudolph Zallinger (the illustrator of “The Road to Homo Sapiens”) the benefit of the doubt here. He could have understood that, contained within his image, are organisms from different Hominid genuses from various times in history: this does not imply progression, just a visual device designed to activate the reader’s almonds… No! Even if this is the case, it suggests that humans evolved from a Chimp-like ancestor just too strongly to be excusable.
The hunched-over, knuckle dragging form, akin to a Chimpanzee, appears near the start of the illustration. It suggests that early Hominins walked like a chimp and then evolved a more upright stature. This isn’t the case. The earliest Hominids (Hominins included) probably looked something like Nakalipithecus (a tree-dwelling monkey-like organism). As the climate changed and trees begin to become fewer in number, the ancestors of Hominins climbed down from the trees and started living a more ground dwelling life; they never knuckle dragged. The ancestors of Gorilla and Pongo evolved knuckle walking independently of each other after they split off from hominins! So yes, shame on you Mr Zallinger.
Moreover, the theory that one small group of AMHs evolved for around 200,000 years and finally travelled “out of Africa” around 60,000 years ago is also wrong. You may be familiar with the phrase “Mitochondrial Eve”. This is from a paper published in 1987 in which human Mitochondrial DNA from 145 different populations was sequenced and made into a gene genealogy tree. The data suggested that through maternal inheritance, all modern-day humans could be traced back to one woman most likely living in East Africa a few hundred thousand years ago. This is also very wrong.
Thanks to the recent meteoric advancement in both gene sequencing and information technologies, much more DNA can be sequenced and compared than ever before. Thanks to the recent sequencing of genes found in the bones of ancient Hominins as well as the sequences of different kinds of genes, many ancestral African AMH groups existing at various time periods have been identified. This throws into doubt the hypothesis that all AMHs are descended from one family group, some of whose descendants left Africa. In fact, it suggests that there were many Hominin groups across Africa, all of whom bred with each other, transferring newly evolved genetic and cultural traits around the continent. Then when some brave humans did venture out of Africa, they were not alone: they kept interbreeding with other groups to leave as well as with different species such as Neanderthals and Denisovans.
There you have it. Most of what scientists used to think about human evolution is incorrect and that bloody cartoon has wilfully misinformed many generations. Alas, at least we can drink milk and beer; they did get that right.