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The evolutionary path to us: straight line or forks in the road?

The depiction of human evolution as a simple linear affair is not only laden with historical baggage, it incorrectly portrays the true complexity of our past, argues Darren Curnoe.

Search "human evolution" in Google images and what you'll get is an abundance of stereotypical images of an idea deeply embedded in our subconscious, the inevitable line or ladder of human evolution:

Step 1, crouching hairy ape resembling a chimpanzee with a bad back;

Step 2, ancient ape learns to squat;

Step 3, ape corrects bad posture;

Step 4, upright ape begins to loose skin colour;

Step 5, almost-human creature has picked up a spear, grown a beard and donned a roughly hewn leather skirt; and

Step 6, big-brained pale skinned man wearing a tailored leather mini (or Armani suit if you prefer) arrives in crowing glory, carrying a beautifully crafted spear (or brief case or even mobile phone).

Now, not only is this a woefully outdated, laconic and highly inaccurate portrayal of our evolutionary history, it's one the plays right into the hands of wannabe scientists like creationists, showing our evolution to be a programmed series of steps leading inevitably to humankind.

This ridiculously simple image would also have appealed to the racialist anthropologists who dominated my field during the 19th and, sadly, a good part of the 20th Century — scientists like Samuel Morton, Carlton Coon and many other race supremacists.

We might well also ask the obvious question: what happened to the other 50 per cent of humanity, womankind? There's more than a hint of Genesis (2:23) about it: "this is now bone of my bones, and flesh of my flesh, she shall be called Woman because she is taken out of Man."

But, what I don't really get is why this kind of drivel still pervades the internet well into the 21st Century and even on some pretty reputable sites that claim some kind of authority on evolution.

So, what's the truth about how we evolved? How should we be portraying the broad sweep of our evolutionary history?

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The ultimate twig

A giant of 20th Century biology, George Gaylard Simpson, observed in a 1964 article in the journal Science in which he poured cold water over the fledgling field of "exobiology" (what we today call "astrobiology") that:

The fossil record shows very clearly that there is no central line leading steadily, in a goal-directed way, from a protozoan to man. Instead there has been continual and extremely intricate branching, and whatever course we follow through the branches there are repeated changes both in the rate and in the direction of evolution. Man is the end of one ultimate twig.

Sadly, 50 years after Simpson wrote these words, the public portrayal of human evolution hasn't changed much, if the internet, many people's font of all wisdom, is truly representative.

The portrayal of evolution as a ladder, just like the equally misleading term "missing link", harks back to the Great Chain of Being of 17th and 18th Century philosophers who believed it was their divine duty to order and name nature in accordance with God's plan: simple things at the bottom and humans, especially the white man, at the top, closest to God.

Carl Linnaeus, the 18th Century father of biological classification, whom we have to thank for the system of scientific names we use today to label all living things, was one such creationist.

He classified humans in the Order Primates and today this label still holds, humankind sitting in a biological group with the lemurs, lorises, tarsiers, monkeys and other apes.

Being dubbed a Primate is one of the highest honours a church can bestow on a clergyman, particularly a bishop, and Linnaeus' classification reflected his bias that humans were also, like clerical primates, close to God.

But, while the label "primate" remains today, religious baggage no longer clouds our ideas about scientific classification.

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Reading the fossil record

Beginning in the first half the 19th Century, anthropologists began to amass thousands of fossils, now spanning a period of seven million years, and this record of our evolution recovered from the Earth's crust shows unequivocally that diversity was the rule.

Latest count is more than 30 species or twigs of two-footed ape (or 'hominin') relatives in our evolutionary bush: or many forks in the road to us, most of them dead ends.

It's true that most of the fossils we have are broken skulls or teeth, sitting in or out of their respective jaws, but just occasionally nature throws up a more complete skull or even nearly complete skeleton for us to find: take Australopithecus sediba as a recent example.

Yet, what's even more fascinating to me, as odd as it may seem, is what we don't know by way of extinct species!

The fossil record is continually throwing up surprises for us when we look in places we've not looked before, or sediments spanning previously neglected periods of time.

Take the Hobbits from Flores (strictly Homo floresiensis), or my own discovery with Chinese colleague Ji Xueping, the 'Red Deer Cave people': anthropologists would never have predicted either of them to have existed based on what we previously knew.

That's the joy of evolutionary science — not to be confused with another biological pastime — just when we think we know it all, along comes another big surprise to forces us out of old habits!

We know very little about human evolution for most of the planet, especially for vast areas like Asia, and even for most of the massive African continent.

Similarly, there are big gaps in time: until the year 2000, the human fossil record ran out at about four million years ago, but then within a few years of each other, new discoveries in Kenya, Ethiopia and Chad pushed it back another three million years, filling a vast chasm.

While the image of the "bush of human evolution" promoted by a bell-bottom wearing Stephen Jay Gould back in the 1970s might not be very glamorous it is the perfect analogy on many levels.

Not only does it accurately portray the evolutionary history of a very diverse, and rather short lived group of two-footed apes, it shrinks our collective ego back to a more realistic and moderated place, right where is should be.

About the author: Associate Professor Darren Curnoe is an evolutionary biologist at the University of New South Wales. He writes about all aspects of evolution on his blog Walking on Two Feet.



In 2008, Curnoe and colleagues discovered the remains of ancient humans dubbed the 'Red Deer Cave people'. This discovery is featured in the documentary Enigma Man: A Stone Age History, which airs tonight on ABC 1 at 8.30 pm.



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