Life is Dangerous — Then and Now

January 20, 2010 | 44 comments

Endangered Species: Humans Might Have Faced Extinction 1 Million Years Ago

A new approach to probe ancient regions of the genome suggests early human populations were scarce

By Carina Storrs   

 

ANCIENT DE-POPULATIONS: Genetic study reveals that populations of ancient humans were surprisingly small.  

New genetic findings suggest that early humans living about one million years ago were extremely close to extinction.

The genetic evidence suggests that the effective population—an indicator of genetic diversity—of early human species back then, including Homo erectus, H. ergaster and archaic H. sapiens, was about 18,500 individuals (it is thought that modern humans evolved from H. erectus), says Lynn Jorde, a human geneticist at the University of Utah in Salt Lake City. That figure translates into a total population of 55,500 individuals, tops.

One might assume that hominin numbers were expanding at that time as fossil evidence shows that members of our Homo genus were spreading across Africa, Asia and Europe, Jorde says. But the current study by Jorde and his colleagues suggests instead that the population and, thus its genetic diversity, faced a major setback about one million years ago. The finding is detailed in the January 18 issue of Proceedings of the National Academy of Sciences.

To make these estimates, Jorde's group scanned two completely sequenced modern human genomes for a type of mobile element called Alu sequences. Alu sequences are short snippets of DNA that move between regions of the genome, though with such low frequency that their presence in a region suggests it is quite ancient. Because older Alu-containing regions have had time to accumulate more mutations, the team was also able to estimate the age of a region based on its nucleotide diversity. The team then compared the nucleotides in these old regions with the overall diversity in the two genomes to estimate differences in effective population size, and thus genetic diversity between modern and early humans.

"This is an original approach because they show that you can use mobile elements…to flag a region of the genome," says Cédric Feschotte, an evolutionary geneticist at the University of Texas Arlington.

The effective population researchers estimate at about 18,500 reveals that the extent of genetic diversity among hominins living one million years ago was between 1.7 and 2.9 times greater than among humans today. (Other studies have shown that the present-day effective population is around 10,000.) Jorde says the reason the modern effective population is so much smaller than the current number of people (nearly seven billion) is that a population explosion occurred, probably due to the development of agriculture about 10,000 years ago. He does not expect that there would have been such a staggering difference between the effective and actual populations of early humans.

Jorde thinks that the diminished genetic diversity one million years ago suggests human ancestors experienced a catastrophic event at that time as devastating as a purported supervolcano thought to have nearly annihilated humans 70,000 years ago. "We've gone through these cycles where we've had large population size but also where our population has been very, very small," he says.

Comments

[Morgan]

Wow. This article is amazing. I cannot believe that there has actually been another time that humans were thought to have gone extinct. 18,000 individuals is a very small number compared to what we have today in 7 billion. These early humans were almost wiped out by a catastrophic weather event in the supervolcano. Should we not learn from our past and realize that global warming is not going to go away just because we are humans and we can survive anything. This article proves that we are not as invincible as everyone thinks. We need to start taking real precautions against global warming or we are going to be in big trouble.

[Sarah Thullbery]

This article is really interesting. With technology and all that scientists and doctors can do today, sometimes it is hard to remember that human beings are not indestructible. It is terrifying to imagine volcanoes or other natural disasters with the ability to wipe out most, if not all, of the human race. I think that one reason, beyond the bottom line, that global warming is not accepted by everyone is the fear of mortality and mutability. I do not think that this is justification for the denial of facts, but it is an explanation.

[Tyler]

Within the past million years, the human race has gone down to a population of only 55,000 at most? Wow...this surprises me! What also amazes me is that they can tell this by simply looking at genetics.

I would like to see the cause of this natural disaster that caused this mass-population decrease a million years ago and 70,000 years ago. Was it global warming? I know that scientists can examine layers of ice to measure the levels of carbon dioxide in the atmosphere at the time.

Either way, I think the one thing we can take from this is that the earth goes through very violent cycles. It's evident that these occur without industrial carbon impact. The fact that we are doing this can't help the situation.

[cdavis17]

I think that this article is pretty interesting, that our population was actually down to only 18,000...that is the size of a normal college. That is crazy. I think that the population now needs to realize this and that we do need to be careful, and actually put some effort into helping global warming from getting worse. OR we may suffer something like the 'Supervolcano' in our lifetime. I do not want my kids to have to go through anything like that in their life either, I want them to be able to enjoy earth like I have and all of my family has. I think that this put some perspective on the issue of global warming and how serious it is.

[mgn]

Whenever thinking about endangered species I would have never guessed that humans were once on the verge to go out. It’s scary to think about humankind failing to adapt to the surroundings. It really makes you wonder about our current situation with Global Warming and how we will withstand to our planet slowly getting warmer. Like Morgan and Sarah said we never look at the possibility of humankind burning out into extinction because our history books never talk of such things. I wonder if now by having the technology to inform us that mankind is susceptible to extinction if it will encourage us to change our ways before it’s too late?

[JohnEvans]

This article is slightly interesting. I don't really see how it effects us today, so I don't really know how to comment. I am always slightly skeptical of elaborate scientific processes like this. It seams like it would be hard if not impossible to do what is claimed. However I am not a scientist so will take their word for it despite my more practical sides warnings. I wish I had the expertise and time to at this in more detail to know more of what they did.

[Brandon]

It is hard to believe that their was only about 18,500 humans walking the Earth at one time. I cannot imagine that at all. I think we should all take note that this could happen again. The human race can be in danger of becoming extinct again if we do not do anything about the global warming crisis. History will repeat itself if we do not find taking precautions and steps to help change the world. We run the chance of their being no humans at all. I wish we could get this type of information out to more people so they know that humans aren't invincible.

[Julie Jackson]

After reading this article I thought of the saying "History repeats itself". That is a scary thought of only 18,000 people. It has happened before so therefore it could always happen again if we are not careful. Also, the picture for this article is crazy looking! I know that before this class I did not know any of this at all. I think that every college student should have to take this class and be informed on what has happened and whats going on. It really makes you want to cherish each day you have. If we do not make any action we could be putting our lives at risk. I know that I want to live a good life without having to worry about tragedies like global warming. A lot of people thought Katrina would be an eye opener, but it was not really so how bad does something have to be to open our eyes before its too late to do anything at all.

[kmcnutt]

I think of how small my town is and how is has about 15,000 people. A little more than that for the whole world? Crazy! A super-volcano is a pretty awesome thing to have wiped out so many species. I wonder how Discovery Channel or Nat Geo would cover that. I don't understand what is means to explain by humans being much smaller than today except that they may be more similar to primates, maybe?
The fact that we are humans, so we automatically can survive most natural phenomena's is a little more than arrogant. We only have the sense to learn to better equip ourselves to adapt. If a super-volcano came, or huge heat waves and storms, I highly doubt many would survive. We need to understand that we are producing this problem and find ways to actively reduce the waste we put out.

[quicktype89]

Wow I never would have thought that humans could have been in such dwindling numbers, but makes perfect sense. I agree with everyone when we say that it is arrogant for us to think that with our technology we can outlast because we see little outside of the comfort of our homes. I also agree with the fear we feel towards the possible wipe-out of man due to global warming. We need to be teaching that we are not invincible and that we too were once endangered species. Perhaps this is something that like preventative medicine, American can work towards-the teaching of "preventative" history as a step towards global understanding of morals and how we treat our world, for the local benefit of our nation.

[Larz]

This is a crazy article. I think it is weird that there was such a small number of people on earth at a time. I honestly don't see it happening again, but you never know it could. It especially could happen if we don't start doing something about global warming, and soon! Like other people said history does have a reputation of repeating itself so you never know. We just need to start being smarter so these kinds of things don't end up happening. More people need to read the articles that we read because I have already learned so much just from these blogs.

[David Cook]

I am so amazed at the depths that science is able to go when it comes to exploring for answers to what happened in our past. It is true that the small number of human beings on the planet at one time is hard to believe, but who knows? If another global warning tragedy occurs then we might just experience an unbelievable extinction again.