Our consciousness sets us apart from all other life. Yet, its evolutionary appearance highlights the accidental nature of our origins, writes Darren Curnoe
The beginning of our species is one of the most significant events in the Earth's — some say the universe's — history. At its centre is answering big questions like the beginnings of consciousness.
The 20th century luminary of biology, Julian Huxley, believed the evolutionary arrival of humans was so profound an event in Earth's history that he dubbed the geological period when it occurred the "Psychozoic Era".
That is, the geological era of the soul or mind.
Contemporary cosmologists like Paul Davies have even argued that the evolution of humans gave the universe self-awareness.
We humans have always thought of ourselves as rather unique in the natural world — even special — a vast intellectual gulf seemingly separating us from all other life.
To reinforce this, we have constructed cosmologies placing humans at the centre of the cosmos: the Sun orbiting the Earth — as seen for example in Ptolemy's geocentric model of the universe.
This view changed of course with Copernicus who showed some 1,300 years later that the Sun was at the centre of universe; well the solar system more accurately, the Earth being just one of several celestial or extraterrestrial bodies orbiting the Sun.
Four hundred years later came the space race. Humans, through the Apollo missions, ventured beyond our Earthly — our evolutionary — home, setting foot on our extraterrestrial neighbour.
We were struck by our seeming aloneness and insignificance in the universe: our pale blue dot of a home set against the vast black expanse of the universe.
This event also marked the serious search for life in outer space, and there's something rather poignant about our desire to see just whether we ARE actually alone in the universe.
So far we seem to be one of a kind. Yet, it hasn't always been this way, being alone I mean.
Living with the cousinsOur ancestors shared the planet with other intelligent life not so long ago — the blink of an eye in evolutionary time — with creatures a lot like us.
Our ancestors shared their world with them for most of our evolutionary history stretching back to around eight million years ago, to the beginning of two-footed apes.
Being alone, as we are today, is the unusual state of affairs.
You've undoubtedly heard of the Neanderthals, Homo neanderthalensis? They lived up until just 40,000 years ago.
The so-called 'Hobbit' — or Homo floresiensis — from the island of Flores. It lived up until around 17,000 years ago.
Or, the Red Deer Cave people, one of my own discoveries with my colleague Ji Xueping, from southwest China. Cousins that lived even more recently, up until about 10,000 years ago.
Arrival of the mindOur species evolved only about 200,000 years ago: probably the newest arrival on the evolutionary scene.
Yet, if we look at the evidence for the behavior our ancestors — the archaeological record — we can scarcely distinguish the behaviour of sapiens-humans from our cousins.
That is, until somewhere in the geological window of time around 50, 60 or 70 thousand years ago. Roughly three quarters of the way through our species' evolution.
At this time, we saw a major event which archaeologists have dubbed the 'Human Revolution'.
At this time we saw the first examples of jewellery being made.
Also at this time, humans took their first steps out of Africa — the humans who went on to the found the world's living populations across the globe.
People lived for the first time in previously unoccupied areas; like rainforests, intensely arid zones including deserts, high mountain ranges, and they quickly settled the Arctic region.
East Asia was also settled about 50,000 years ago for the first time by humans, as was the island continent of Australia.
All of this occurred about the time our kind left Africa. Not earlier, and sometimes a little later. And despite the fact we had existed as an unremarkable species for around 150,000 years.
We saw the first cave paintings at this time, in Europe, Asia and Australia. Symbolic representations of the internal and external world through vivid paintings of cave and rock shelter walls.
And we saw a much wider range of tools being made, with rapid innovation in tool form and use.
Tools called 'microliths': tiny tools that replaced in many places the bigger, chunkier tools made by our earlier ancestors and relatives.
In short, we saw humans in all of our glory: with our vivid internal world and imagination, and living in virtually every nook and cranny the planet has to offer.
Gift from a departing relativeSo, why the 'Human Revolution' then and not some other time during the 200,000-year span of our species?
We can piece together the evidence to develop a rather surprising scenario: a truly remarkable narrative of our origins, based on the latest science.
At about 60,000 years ago, when our human ancestors were beginning to make their journey to settle new parts of Africa and the rest the Old World the planet was a very different place to today.
It was a world inhabited by our close relatives: cousins living in parts of Africa, and in Asia and Europe.
Now, something rather extraordinary seems to have occurred about this time, as has been shown by the work of some very clever geneticists.
When our ancestors moved into these new places they did something that seems to be a first in human evolution — they mated with the locals.
Now our genome, it turns out, is like a patchwork quilt. It's estimated that up to five per cent of the DNA of people living in North Africa and outside of Africa today comprises Neanderthal genes.
And a similar value also for the Denisovans — a mysterious species from Siberia we know from a single tooth and finger bone, but also its genome.
It might strike you as odd that different species interbreed. But, in fact, between species mating is common in nature and is actually an important source of evolutionary innovation right across life.
The Denisovans, for example, probably gave us a raft of genes associated with immune function and genes that allowed people living today in the Himalayas to survive at high altitude.
Accidental origin of usThere's another really fascinating and potentially profound genetic gift they gave us on their way out: a variant of the microcephalin gene.
This gene plays a key role in brain size in humans and there is ample evidence it has been under strong selection in recent evolution.
Now, genetic studies suggest this gene may actually have been added to our genome through interspecies interbreeding with a close cousin. Maybe even with the Neanderthals.
I don't wish to suggest this is THE gene for consciousness, for without doubt something as complex as the human mind or consciousness must involve multiple genes or even networks of genes.
But, the microcephalin gene is likely to be a key gene, without which consciousness might not exist.
So, it could be that the psychozoic of Huxley, or the universal consciousness of Davies, resulted from the incorporation of a gene we received from a close evolutionary relative.
Isn't this the ultimate irony? We get the gene, send them to extinction, and claim universal consciousness while we're at it!
Science constantly updates and knowledge progresses. And, without doubt, this story will change as well. But, in the end, this doesn't really matter because it highlights one really important aspect of our evolution.
It is clear that we humans, and our remarkable consciousness, were not planned, nor inevitable, and not built into some design for the universe or the fabric of the cosmos.
Instead we were accidental, our evolution contingent.
The very feature we hold so dearly may in fact result from a chance encounter in a dark alley, even an evolutionary one-night stand.
This article is based on a TEDX Brisbane talk given on 5 October 2014. A longer version is available on Walking on Two Feet.
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 blog. His work with colleague Ji Xueping is featured in the documentary Enigma Man: A Stone Age History. He also appears regularly on ABC 702.