The biggest expansion of man in prehistory?

October 30, 2012
A rooted genetic family tree of 36 Y chromosomes.

DNA sequencing of 36 complete Y chromosomes has uncovered a previously unknown period when the human population expanded rapidly. This population explosion occurred 40 to 50 thousand years ago, between the first expansion of modern humans out of Africa 60 to 70 thousand years ago and the Neolithic expansions of people in several parts of the world starting 10 thousand years ago.

This is the first time researchers have used the information from large-scale DNA sequencing to create an accurate family tree of the , from which the inferences about human population history could be made. Since the Y chromosome is found only in men, its history and evolution are easy to study and interpret.

This study also highlights how information generated by other , in this case by the company , can be used to investigate human genetic archaeology. The lengths between the branches and the length of each branch on the Y chromosome family tree provide insights into the evolution of the human population. The closer the branches are, the more rapidly the population was expanding and separating, most likely into different geographic areas. The longer the branch length, the greater the time that group of people have been separated from the other groups.

"We have always considered the expansion of humans out of Africa as being the largest population expansion of modern humans, but our research questions this theory," says Ms Wei Wei, first author from the Wellcome Trust Sanger Institute and the West China University of Medical Sciences. "The out-of-Africa expansion, which happened approximately 60,000 years ago, was extremely large in geographical terms with humans spreading around the globe. Now we've found a second wave of expansion that is much larger in terms of human population growth and occurred over a very short period, somewhere between 40,000 to 50,000 years ago."

There is no obvious archaeological event that would explain why this sudden expansion in the human population occurred. One possible theory is that during the original out-of-Africa expansion, humans moved along the coastlines of the world, settling as they went. Their origins and genetic makeup would mean that these people were suited to coastal life, but not to the demands of living inland. This would have prevented large population growth as the coasts could only sustain a certain number of people.

"We think this second, previously unknown population boom, may have occurred as humans adapted to their new environment after the first out-of-Africa expansion," says Dr Qasim Ayub, lead author from the Wellcome Trust Sanger institute. "We think that when humans moved from the horn of Africa to Asia, Australia and eventually Europe, they remained in small groups by the coasts. It took them tens of thousands of years to adapt to the mountainous, forested surroundings on the inner continents. However, once their genetic makeup was suited to these new environments, the population increased extremely rapidly as the groups travelled inland and took advantage of the abundance of space and food."

The work highlights how it is now possible to obtain new biological insights from existing DNA sequencing data sets, and the value of sharing data. The majority of the DNA information used for this study was obtained from freely-available online data-sets.

"We have provided a nearly ten-fold increase in the number of genetic markers found on Y chromosomes and discovered new historical insights into the evolution of using DNA sequencing information from just 36 men," says Dr Chris Tyler-Smith, lead author from the Wellcome Trust Sanger Institute. "We now want to look at ten times this number of Y chromosomes in data from the 1000 Genomes Project. Who knows what we will find then?"

Explore further: Spread of endogenous retrovirus K is similar in the DNA of humans and rhesus monkeys

More information: Genome Res. 2012 doi:10.1101/gr.143198.112

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3.3 / 5 (3) Oct 30, 2012
I wonder if this has anything to do with the population bottleneck humans underwent during the Toba volcanic eruption
4.2 / 5 (17) Oct 30, 2012
However, once their genetic makeup was suited to these new environments, the population increased extremely rapidly as the groups travelled inland and took advantage of the abundance of space and food."
But our genetics differ little among subgroups. Perhaps it was a certain tech advance such as the spear thrower, bow and arrow, or novel way of making or using fire which spread among tribes in the same way as the Clovis point, which gave them an advantage.
1.4 / 5 (5) Oct 30, 2012
(I bristle when I read stuff like I'm about to write but I've been digging for a long time on this subject and...)

We couldn't have ~always~ had religion. Given its power it's rational to think of it as being a tremendous competitive advantage (think of it as the first Internet too...).

Anyone know from whence the first religious artifacts show up in the fossil record?

I am inclined to believe that religion evolved in order to control violence (four separate categories of violence but that's too long). I think that best suits the maximum number of observables especially the principle of evolution.

I would expect to see a population explosion at the same time in history as the founding of the first practical, sustainable, religion. (in the modern "control everyone" sense)
2.6 / 5 (9) Oct 30, 2012
No, religion is the source of much of the violence we see around the world today. A successful long term civilization and violence are incompatible. It really boils down to having more children than you or your civilization can raise without resorting violence to provide for them.

4 / 5 (2) Oct 30, 2012

The spread of one religion would be more likely to reduce the variation in genes, as one group got organized and spread dominion over others. If it is connected to the increase in variation, then it would be because people with different religions fought and separated from one another.

The article points to humans moving into different geographical regions, which is much more likely as a driver of genetic differences. That's how it works in other animals, no reason why it should be different for humans.

Their cause-and-effect is presented backwards, though. The populations on the coastline were really one contiguous population. Humans would have been trying to move inland the whole time, but they'd fail to thrive there for a long time. Then they'd develop adaptations that enabled survival inland, and the population grew in distinct regions. At that point, you'd get genetic drift as populations became isolated, not more population because their genetics were different.
3 / 5 (2) Oct 30, 2012
"This would have prevented large population growth as the coasts could only sustain a certain number of people."

There were less than a million people living before 10,000BC, spread across half of the earth. I am not sure why the author thinks that the oceans couldn't sustain that kind of population.
not rated yet Oct 30, 2012
The oceans could have, but were fishing techniques capable of supplying enough food for more?
1 / 5 (2) Oct 30, 2012

You might enjoy Julian Jaynes' "The Origins of Consciousness in the Breakdown of the Bicameral Mind." Not without some controversy, Jaynes theory of the origins of consciousness includes the origins of religion. In fact, one could say that, according to Jaynes, religion was a precursor to consciousness- a way of replacing what bicameralism had provided for so many generations previously. There is a great deal of material about the book, the theory, and the man, online.
5 / 5 (3) Oct 30, 2012
I don't know if the model is good, but the presented hypothesis seems to go against observation.

We know humans populated "the mountainous, forested surroundings on the inner continent[s]" of Africa. And the Denisovan result, with some factual inland finds, would be difficult to predict from a coastal bounded migration.
5 / 5 (4) Oct 30, 2012
@ eaq97a:

You know "the population bottleneck humans underwent during the Toba volcanic eruption" is more or less a lone anthropologist (Ambrose) controversially supporting the timing, right? The modern genome material put bottlenecks on all three human species (moderns, neanders, denisovans) early on. That is way before the Toba event. [ http://en.wikiped...e_theory ]

And there are evidence of mostly unbroken population of the neighborhood of the presumed event, which wasn't all that compared to similar ones. The simple prediction is that it is a lone anthropologist crusader without much of a factually supported cause. There are many of those.

And I am, quite frankly, tired of seeing lone and loony ideas repeated, without reference to the research, as if they were fact or even uncontroversial.
1 / 5 (4) Oct 30, 2012
A successful long term civilization and violence are incompatible.

uh huh

Rome, Mongol, Mayan
4.3 / 5 (6) Oct 30, 2012
@ loneislander:

Plenty of statistics shows that religion feeds of (and perhaps feed, but I think that is less evidenced) social insecurity that comes out of previous tribal societies and recent dictatorships. [See Paul & Gregory.]

The lessened violence that we can see in modern societies correlate AFAIK with the rise of secular moral societies, i.e. democracy et cetera. [See Pinker's last book, said to have excellent statistics. And Rosling's statistics re modern functional vs dysfunctional societies.]

Belief in belief is a cute religious meta-phenomena, but it is of course totally unwarranted by facts.
1 / 5 (3) Oct 30, 2012

I'd like to hear your thoughts on the advantage of not being religious in the early times of human evolution.

It has been argued that the display of religiousness showed reliability of the individual, thereby making him/her a more attractive mate. Since religiousness is (at least) partly heritable, one would expect to be a little more dominating with every generation.

Looking at people today, I do not see any particular advantage in terms of inventiveness for the atheist. So, if this was true a hundred millenia ago, you would expect practically all humans to be atheists. So, why are there atheists?
3.7 / 5 (3) Oct 30, 2012
I seem to remember from "Guns, Germs and Steel" Jared Diamond positing that early tribes probably had strict taboos against killing kin (and most within a tribe would be related), but not against killing non-kin. With the advent of big religion (big in terms of powerful deities, not spirits), people could be grouped based on common deities. Religious and political leadership classes grew in power, with the rulers usurping the power to commit violence. They could do this because of the support of the religious leaders, who provided rulers with a "god given mandate" to rule. This organizing principle enabled tribes to conquer and assimilate other tribes, growing more powerful.
1 / 5 (3) Oct 30, 2012
Bottle necks and explosions are either related to plagu/immuno-resistance or food availability changing dramatically. Thats my armchair guess.

1 / 5 (4) Oct 30, 2012
Perhaps hybridization with Neanderthals played a role?
2.7 / 5 (7) Oct 30, 2012
Religion does not cause or suppress violence it simply structures it. Other aspects of society adapt to the new structure which reinforce the religion while benefiting from the predictability imposed on human aggression.
1 / 5 (3) Oct 30, 2012
A successful long term civilization and violence are incompatible.

uh huh

Rome, Mongol, Mayan

Your point being?

How long did the most violent, the Mongol civilization last? The Mayan civilization very likely collapse from within because of the violent they practiced among themselves.

As for the Greeks and Romans they may have been violent to outsiders but they had rules of law to keep relative peace among themselves. After all the concept and practice of democracy and monogamy came from the Greek and Romans.
not rated yet Oct 31, 2012
@loneislander - Spirituality vs religion.. how long ago did someone first believe a material item held a special significance? I like the question.

I believe spirituality came long before religion. We humans see patterns everywhere and attribute significance where there might be none. We suspect and sense there is a great deal more than we can actually sense.

I think some of us need to perceive the rest of us believe as we do. That leads to violence. Some of us do not take issue with others being different than us. That way leads to cooperation.

I think we all (individuals, groups, cultures, species) change our minds, like genetic diversity, over time from strict to lax on all subjects.

So, I think religion does not necessitate violence. Known history has enough examples of long term peaceful co-existence and even symbiosis.
not rated yet Oct 31, 2012
@Jeddy McTedder - What is the difference between an expert and a layman? (I say this from my armchair.) I think the expert has owned an armchair for a long time AND has gone out into the world to prove or disprove their own hypotheses. In the process of actively being in the world and not so much inactively in their armchair, they learn something.. And want to tell all their friends and impress their enemies..
not rated yet Nov 03, 2012
We humans see patterns everywhere and attribute significance where there might be none. We suspect and sense there is a great deal more than we can actually sense.
And just as often we do not attribute significance where we should. Both conditions are representative of ignorance. Happily ignorance is curable, eventually.
1 / 5 (2) Nov 04, 2012
Responding to Pressure2 (four above), the Mongols had a pretty good run--from about 1215 (Genghis, of course) to about 1858, when they folded officially in India. They covered a lot of geography, controlled many different ethnic groups, and even when weak in the 1800s exercised some dominion and control over more than 100 million Indians.

Addressing the dialectic between LoneIslander and Pressure 2 (back-to-back posts near the top), there is some truth in both views. Coherence within a large group of individuals is useful: less friction, more output per unit of energy. Like solid, liquid, gas. Emotionally, we all tend somewhat in this direction. Greater population density eventually produced 5 or 6 emergent religions from 500 BC to 600 AD. Useful coherence. At the boundaries, this of course produces plenty of violence. As traditional religion fades in the US, new ideologies emerge resulting in emergent coherent groups--though the practitioners usually disdain "religion."
1 / 5 (1) Nov 04, 2012
@Torbjorn_Larsson I'm not stating it as a fact, all I'm saying is there might be a connection. The Toba theory as well as this one here are all subject to critiques and informed debate and as far as we all know scientific progress is all about repeated confirmation or contradiction and in this case as with so much else it is still up in the air

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