A TIMELINE FOR THE PLANET click for Home Page

Modern humans appear

Opinions differ about when modern humans emerged. Around 200 ky seems about right these days, though this is a good deal earlier than used to be thought.

Taking over the planet The Genetic contribution The Rise of Culture Weaving & the Venus figurines language & symbolic thought the Neanderthals

It was during the worst glacial period. Our immediate predecessors are believed to have been a fairly insignificant species, Homo. antecessor.

Part of the reason why our arrival time is uncertain is that, to begin with, we made very little impact. For possibly 150,000 years we continued to live the primitive lifestyle of our forebears. Then, as we’ll see later, we exploded on to the scene and changed the world.

It’s thought that we began like this.

Towards the start of the cold period, a small group of H. antecessor may have been isolated in a small haven in East Africa, possibly near the mouth of the Red Sea. It seems that Sumatra’s Mount Toba erupted and produced a 100-year long ice age. My guess is that Toba’s emanations actually had a longer-term effect than that. So, for possibly quite a long time, these guys were suffering from seriously hard times.

Geneticists believe that there was a time when there were only some 10,000 of us, and that our total population remained that small for “a long time” (whatever they may mean by that). And this period seems as good a candidate for such a ‘bottleneck’ as any. The reason they believe this is that the variation in human DNA is extraordinarily small. A single group of chimps has wider DNA variation than the entire human race.

But that’s not all. The DNA variation of the world’s non-African population is much smaller still. I’ve read that a single African village has more variation in its DNA than that of the entire rest of the world. We’ll discuss why this might be later.

We should mention the ‘Aquatic ape’ theory. It’s a highly controversial theory that evokes strong passions on both sides. It suggests that we may have had to take to the water at some point, and that to survive we had to become semi-aquatic. The only evidence for the theory lies in certain features of modern humans. But some of these are quite striking – like our exceptional swimming ability, or the fact that we can safely give birth underwater. Even today, our babies are born with the right instincts and capabilities to cope. There’s also the layer of fat that we have under our skin. This is ‘buoyant’ white fat, not insulating brown fat. Many aquatic animals have this, but no other ape does. There are other striking features too.

Many scientists reject the idea completely. No hard evidence, you see. But I’ve always been a bit of a water-baby and I fancy it. If there was an aquatic phase then again this seems as good a time as any for it to have happened. We must remember that Darwin found the folk of Tierra del Fuego living naked in temperatures around freezing. They were quite happy to swim in water with ice chunks floating in it!

The Neanderthals appear to have emerged in Europe from Homo erectus, at about the same time as we evolved in Africa from H. antecessor. Although anatomically we were significantly different, we lived very similar lifestyles for a long time. This is rather odd actually, but it does seem to be so. The Neanderthals had icy Europe to themselves and we occupied warmer Africa. We even appear to have used the same toolkit (more). It’s not clear which of us invented it.

How was this possible? We did have an opportunity to sample each others’ toolkits during the last interglacial, some 120,000 years ago. We expanded northwards and the Neanderthals expanded southwards. And the common ground was Israel. Note the weasel words though. I’m not clear whether we met face to face, or whether the see-sawing weather led to us taking turns to occupy the same set of caves. Either way we would each have been introduced to the other’s tools and other artefacts. There’s usually only one ‘right’ way to make a tool. Modern flint knappers have ‘reverse engineered’ many ancient toolmaking techniques, purely by experiment. Both we and the Neanderthals were certainly smart enough to do the same (more).

We may have reached southeast Asia. But we still didn’t make much impact. The Neanderthals remained in charge in Europe and Homo erectus in Asia. Then the cold returned with a vengeance and we had to retreat back to Africa.

Taking over the planet

Modern humans were not the first to expand out of Africa and to take over other parts of the planet. This prize goes to the mighty hunter, Homo erectus, nearly 2 million years ago – or possibly to the even earlier australopithecines, see the same link. And, between ice ages, folk have been living as far north as Britain for quite a lot of the time since.

As we’ve just seen, modern humans had a go 120,000 years ago. But it didn’t work out.

Then, about 45,000 years ago, the climate warmed again and a small group of us had another go. I say ‘small group’, because that would explain why the DNA of the rest of the world is so much more restricted than that of the African population. (We may have done it in two waves, 60 and 40 odd thousand years ago. Reports differ.)

This time we swept all before us. We drove Homo erectus from southeast Asia, and we drove the Neanderthals from Europe. The details of where we had reached by various times is ‘subject to considerable debate’. So we won’t get bogged down in it.

But an article in New Scientist (27.10.07) gives what seems to be the latest theory, as this map shows. The broad arrows indicate general movements, as indicated by genetic studies. The narrow ones suggest possible actual routes. The article doesn’t explain the blue arrows, depicting Atlantic and Pacific crossings.

Apparently there were two routes north from our possible refuge. One was through the Sahara desert. There were various times when the Sahara was humid and inviting. So if the timing was right, this could have been an attractive route. We mentioned earlier our primitive ancestors, the Australopithecines. They are thought to have wandered aimlessly northwards, right out of Africa and into eastern Asia millions of years before, ‘just following the grass’. We must imagine these modern humans doing much the same. They needn’t have been on any great mission to populate the planet. They could simply have been following their food source and/or seeking better living conditions. We discuss later that a population explosion may have had something to do with it. Unfortunately it’s not known what the region was like at the appropriate time, and therefore whether this route was actually plausible..

The second route is across the mouth of the Red Sea and up the coast. Interglacial or not, this was the depth of the Ice age when the sea level was much lower. So the crossing would have been easy. The evidence is all gone under the rising waters. But it’s known that these folk were into seafood, so this route would have provided good eating whatever the climate. To me the coastal route seems much more plausible. But then I like the idea of our already being into boats. This same link discusses the theory that, much later, the same folk found their way to America, again by the coastal route. On this occasion they were ‘just following the kelp’, which is home to a particularly rich seafood fauna.

Colonising south-east Asia and even Australia was fairly easy, because again, all folk had to do was to follow the coast. We appear to have reached Australia within some ten thousand years of leaving Africa. We will have had to do a bit of seafaring, though it’s not clear how much because sea levels were much lower at that time. H. erectus was already there of course. But I’ve not seen how much of a problem they were for us.

But expanding northwards was more of a problem. It seems to have taken another then thousand years for us modern humans to follow the Australopithecines into eastern Europe, for example. Not only was it colder for us, and we had to invent warm clothes. But the Neanderthals were already there, and pretty well as advanced as us. I’ve read that it took about 10,000 years to supplant them. During that time we seem to have co-existed, with a certain amount of interaction. Did we interbreed? Opinions differ.

America was an even bigger problem and, as we’ve seen, it took a lot longer still.

Why were we so much more successful this time? Theories abound. Warm clothes are nowhere near enough to explain it. Our brains seem to have remained exactly the same size although, as we discuss elsewhere, intelligence and brain size don’t go together nearly as closely as you might think. Some scientists argue that our ‘small group’ acquired a mutation that improved the way our brains were wired up.

The Genetic contribution

As we’ve said, the broad arrows on the map reflect what genetic evidence is telling us. Genetic evidence has had a chequered history.

The theory goes thus. Organisms’ genomes are continually acquiring minor mutations. There’s no ‘method’ to this. They appear in a thoroughly disorganised and random fashion. Some prove beneficial, and help the organism in its fight for survival. Even if the benefit is small, beneficial mutations become more common. Other mutations of course are harmful, so naturally they become rarer.

But the vast majority of these mutations have no practical effect at all. They just accumulate, at a roughly constant rate, for maybe hundreds of millions of years. Inter-breeding ensures that all the members of a particular species carry the same selection of useless mutations. (That’s the theory anyway.) But when a species splits into two, this interbreeding stops, and each group starts to collect its own selection.

So geneticists can count (maybe ‘estimate’ is a better word) the number of mutations that each branch has acquired since the split. This enables them to put a number to how long ago the split was.

The trouble is that the geneticists made the same mistake that so many other scientists make, to their eventual cost. As we’ll discuss shortly, they made an assumption that they didn’t realise that were making. Scientist often do this. The high and mighty cosmologists are some of the worst culprits, as other cosmologists keep telling them (more). These assumptions can all too easily be wrong. As a long-term student of the Earth story, I’ve seen scientists having to back-track many times.

The geneticists assumed that there was some mystical genetic clock that controls the rate that any genome acquired these mutations – and that this clock has run at a constant rate over the entire period of interest. As we’ve said when we’ve met this problem elsewhere, in a sense they could do no other. If that’s all the evidence you’ve got then you have to do your best with it. The trouble comes when you actually start to believe it. And this is exactly what so many scientists do.

When the geneticists started getting dates that conflicted with other evidence, they announced that they were right, and that the other findings were wrong. (This may have been a long time ago, but we chroniclers suffer pain when scientists make stupid and arrogant claims – and we have long memories!)

But then (the shame of it!) the geneticists started getting different answers according to which part of the same genome they studied. They eventually got round to doing what we engineers have always done (big money and even lives can be at stake in our work). They started checking out their assumptions properly before deciding how much weight to give them.

In brief, they are now much more careful, and much less arrogant. As a result their results are taken considerably more seriously.

The genetic evidence indicates a rapid expansion along the coast into India, a slower one along the eastern Asia coast ending up at the Bering Strait, and a slower one still through the heart of Asia. Finally we have the slowest one of all, along the southern Asia coast, down towards Australia and up along the coast again towards the Bering strait. Why was this migration so slow? Maybe because the living was good, and folk had not real incentive to move on. Migrating northwards is not really something that you would do for fun.

It took a very long time for us to get across from Asia to America. But we discuss this in greater detail under sail.

But that’s not the end of the story. Apparently genetic evidence, taken from modern populations, can estimate the rate of population expansion at different times and in different places. It sounds a bit unlikely to us uninitiated, but it has to do with the famous mitochondrial DNA. The mitochondrial DNA evidence points to a population explosion between 70 and 80 ky ago, “perhaps in a small source region in Africa” (the same N.S article). The theory is that it was sparked off by an improvement in technology, social arrangements (and culture?). This could have sparked off the initial expansion that we discussed earlier. The same line of evidence also points to a population increase in southern Asia around 60 ky ago, leading to the assorted expansions eastwards.

We have to point out that, plausible though this theory is, the proponents of rival theories dispute it.

And here’s another twist. Apparently between 150 and 70 ky ago, the climate in Africa kept oscillating between drought and flood. So our ancestors had to keep adapting or dying. Maybe there was a good deal of dying. Then, from 70 ky on, the climate stabilised in a damp phase. This will have taken the pressure off, and fostered the population explosion.

The rise of culture

We suggested earlier the theory that a genetic mutation triggered our great exodus. But some scientists believe that a step change in culture is all the explanation you need, and they could well be right. There have been pretty major step changes in culture since then, and nobody is explaining these in terms of any mutations. The ancient Britons, for example, took to the heady new Roman civilisation like ducks to water. That is to say, the tribal leaders did. I suspect that the ordinary folk lost out badly. The Industrial revolution brought huge changes in its wake, even more quickly.

Not all scientists agree that our change in culture was all that sudden anyway, e.g. Kate Wong in Scientific American June 05. ‘Sudden’ developments do have a habit of evaporating as more evidence comes in.

In the case of culture the answer appears to depend on where you are looking. In Europe, where most of the evidence is, the arrival of advanced culture genuinely does appear to have been moderately sudden. But if you go back to Africa, you find developments happening much earlier, and in a much more gradual and piecemeal fashion. This fits in with the idea of a group of us breaking out of Africa, and bringing the new advanced culture with us. And we mustn’t forget that the Homo heidelbergensis folk of ½ million years ago were already living a pretty good and highly social life (more).

We also mustn’t forget the old adage “absence of evidence is not evidence of absence”. We can’t prove that certain ancestors were doing this or that until we find evidence. But we certainly can’t say that they were not actually doing it long before – particularly if, like fire or personal adornment, it would not readily leave evidence. For example, there are wall paintings aplenty in Europe, where they were done in caves. In Africa hardly any have been found so far, because they were done on rocky outcrops. Should we say that wall painting was a European invention? Certainly not.

It also depends, as so often, on ‘exactly what you mean by …’.

The strict definition of ‘culture’ is the ability to learn from your mates, and many of the higher animals do this. I’ve read that first-time chimpanzee mothers have to learn how to suckle their young from more experienced mothers. Is this culture? The normal test for culture is that different unconnected groups do things differently from each other. They may all make tools for extracting termites from their nests. But they use different techniques for fashioning them. It would be fascinating to know how different groups of chimps teach new mothers how to suckle.

But now we’re using ‘culture’ to mean something much more sophisticated. I suspect that different scientists mean different things by it too.

This diagram comes from the Scientific American article. Wong has chosen to interpret ‘culture’ as beginning with stone ‘blades’ ½ million years ago. This is pretty arbitrary. The first stone tools so far found are actually 2½ million years old (more). But she had to start somewhere.

Wong’s blades were found in Kenya, and dated to 510 ky ago. We discuss elsewhere the Butchers of Boxgrove in England, who were making exquisite handaxes fairly shortly after this (I’m not clear on the precise date). They were also hunting big game, and butchering the carcases expertly on the spot (well you wouldn’t want to carry a horse or rhino back to camp whole would you?). Good butchery requires sharp blades!

We also discuss, at the same link, the exquisite throwing spears made near Heidelberg at around the same time. If sharp blades are an indication of culture then surely these spears are too.

Neither of these folk were ‘us’. I don’t know about the Kenya people, but the Boxgrove guys seem to have been Homo heidelbergensis, the makers of the spears and the ancestors of the Neanderthals.

The diagram is not very clear. But it shows a progression of new inventions, from ½ million years ago to 40 thousand. One of the first, at around 850 ky, is ‘pigment processing’. This is normally interpreted as implying personal adornment, a cultural activity if ever there was one.

Then comes a long list of technological inventions, such as fishing, working with bone, making barbed spear and arrow heads, and so on. But there’s also long-distance trade, at 140 ky. You can’t imagine this happening without a fairly sophisticated culture. And ‘incised notational pieces’ have been found at 100 ky, which are taken to imply counting or even trade and accounting.

Beads appear, in Africa at least, at around 80 ky and these are they. They were found in Blombos cave, 200 miles from Cape town. They are snail shells, collected from an estuary 12 miles away – which was a long way to go just for their food value. However wear marks around the holes suggest clearly that the shells were strung together to make a necklace or bracelet. You can’t get more cultural than that either.

Finally come ‘images’ at some 40 ky (more). These early images were pretty crude, and I’m not sure how many scientists regard ‘culture’ as starting quite as early as this. In any case, what they should be saying perhaps is ‘advanced culture’ or something, to make it clear that they understand how much they are leaving out.

Weaving and the Venus figurines

I’ve read that folk were already into advanced weaving techniques by 28 thousand years ago. No woven material has survived, not surprisingly. The evidence comes mainly from archaeological sites in the Czech Republic. Apparently they show clear evidence of sophisticated weaving and plaiting techniques, netmaking, plaiting and coiling baskets, dating back to this time.

There are also artefacts such as the ‘Venus figurines’, of which this is the most famous. It’s the Venus of Willendorf found, surprise surprise near Willendorf in Austria. Its date is uncertain, except that each re-dating seems to put it older. The latest I’ve seen is 30-25 ky. This one fits neatly into the palm of the hand.

The sexual importance of the figurines is very obvious, and for a long time any other possible significance was overlooked. It was originally assumed, for example, that they were carved by men.

But I’ve read a report (New Scientist 6 May 2000) that suggests otherwise. This one is naked, apart from its ‘woolly’ hat. To you and me, it looks like a woolly hat, and this article insists that that is what it is, except that it needn’t have been made of wool. Other scientists however have interpreted it as exquisitely plaited hair. This may be because it hadn’t occurred to them that weaving could have got going so early. It now seems that, if you study other figurines carefully, you see unmistakable signs of woven clothing as well as hair adornment.

Not only that, but they display detailed knowledge of weaving and plaiting techniques that the article suggests only an experienced weaver and plaiter would be aware of. If this is true, then it implies that the figurines were actually carved, not by men at all, but by women. (Either that, or the men did the weaving!) If this becomes accepted then it will set the cat among the pigeons in a big way.

One could doubt all this of course. A carver who is truly dedicated to his art might well wish to capture the finest detail of his subject. And he will presumably have had a mate to consult over anything that puzzled him. They may not yet have had ‘language’ as we currently know it. But I don’t see how we can possibly doubt that they could communicate pretty well.

What is indisputable, it seems, is that the folk of the time were heavily into vegetable materials for making clothing and other things.

Language and ‘symbolic’ thought

With advanced culture is held to have come symbolic thought. Symbolic thought is a somewhat hazy concept to most of us. Scientists believe that it emerged with advanced culture. Between them they constituted a huge advance on anything that went before. Note the weasel words ‘is held to have’ and ‘scientists believe’. There’s no evidence that the two were linked. Neither could there be. And some scientists theorise that symbolic thought emerged as soon as we, Homo sapiens, appeared at least 150 thousand years before. That is to say symbolic thought evolved as soon as our brains could cope with it. There’s no sign of cultural activities anything like as early as that. Well there is actually. The Boxgrove folk seem to have been making handaxes ‘for show’ hundreds of thousands of years earlier still (more).

But assuming the mainstream view is right, then a much more complex language had to develop at the same time. And fairly quickly at that. This is reckoned to be the point at which ‘communication’ turns into language proper. When you have mastered symbolic thought, you suddenly need to be able to say a wide range of new things. So you need a much more sophisticated method of communication to enable you to say them. For the first time, you need a fully-fledged language as we understand the notion today.

If symbolic thought came with advanced culture, then it’s clear that we are talking about a purely cultural breakthrough. There seems to have been no difference whatever between the folk who lived before and after it emerged. This needn’t surprise us too much. There was no difference between the folk who lived before and after writing was invented, or advanced civilisations emerged such as the Egyptians or the Greeks. And it may surprise the young, but those of us who were alive before the computer age are exactly the same as those who grew up after.

However for my part, I’m with Wong in believing that the whole process was actually a good deal more gradual than many scientists currently believe. Indeed, I would probably go even further than Wong (more). ‘Man the mighty hunter’ (more), of well over a million years ago, wiped the sabre-toothed tiger from the face of Africa. He had no throwing spears or bows and arrows. Evidence for spears first appears a million years later, partly in the form of animal shoulder blades with holes in them (more). Without ‘distance’ weapons, he will have needed some pretty sophisticated concepts to plan and execute the hunting of such dangerous prey.

Richard Cowen (of History of Life fame) has a different reason for thinking that language started early. He reckons that it had to do with the taming of fire by the ‘mighty hunters’. And this seems to have been by the same folk, some 1½ million years ago.

Were these guys into the cruder elements of symbolic thought? I would have thought so. But it probably depends on ‘exactly what you mean by’ – symbolic thought.

To make the sounds that we use for speech these days, you also need mechanical adaptations to the larynx and breathing equipment. Our predecessors don’t seem to have had these. Did they evolve under pressure of the need to make a wider range of sounds? Or did we simply exploit what we acquired for some other reason? My guess, like so much else in science is – a bit of both.

The Neanderthals

It’s interesting that the Neanderthals developed an advanced culture pretty well at the same time as us. It wasn’t quite the same, but it was remarkably similar. We strung animal teeth into necklaces, and so did they. But we bored holes in the teeth, whereas they cut notches to help the ‘string’ to get a grip. We made pendants, bone tools and knives. And so did they. But the techniques used were different.

The Neanderthal culture is called Châtelperronian, whereas ours is called Aurignacian. There are arguments over whether the Neanderthals copied their culture from us. But I’ve read a report in Scientific American (April 2000) that says that in fact the Neanderthals got there first. However it would be more than my life was worth to suggest that we copied from them!

I’ve read conflicting reports about how much better our Aurignacian toolkit was

The ‘Cro-Magnon’ folk who took over Europe were only a small outpost of the H. sapiens population. But they seem to have left far more than their fair share of evidence about how they lived. This could be because they had to live in caves. And caves are very good for preserving evidence. There seems little doubt that the Cro-Magnons had the edge on the Neanderthals in almost every area of endeavour. This picture of a Cro-Magnon is by Zdanek Burian.

The Cro-Magnons had richer and more sophisticated art and tools. And they used stone-tipped arrows and spears. The Neanderthals’ Mousterian tools were designed for woodworking. But the Aurignacian kit (more) that the Cro-Magnons brought with them enabled them also to work with bone, antler and stone.

More about the Neanderthals

© C B Pease December 07