Human Ancestors Were an Endangered Species -- Gibbons 2010 (119): 2 -- ScienceNOW
AAAS.ORG
FEEDBACK
HELP
Daily News
LIBRARIANS
Page 1 of 3
Enter Search Term
ADVANCED
GUEST ALERTS | ACCESS RIGHTS | MY ACCOUNT | SIGN IN
All Free Articles
Top 10 Last Month
ScienceShots
Daily News Archive
About ScienceNOW
Home > News > Daily News Archive > 2010 > January > 19 January (Gibbons)
ADVERTISEMENT
Human Ancestors Were an Endangered Species
Enlarge Image
By Ann Gibbons
ScienceNOW Daily News
19 January 2010
With 6.8 billion people alive today, it's hard to fathom that humans were ever imperiled. But 1.2 million
years ago, only 18,500 early humans were breeding on the planet--evidence that there was a real risk of
extinction for our early ancestors, according to a new study. That number is smaller than current figures for
the effective population size (or number of breeding individuals) for endangered species such as
chimpanzees (21,000) and gorillas (25,000). In fact, our toehold on the planet wasn't secure for a long
time--at least 1 million years, because our ancestral stock was winnowed with the emergence of our
species, Homo sapiens, 160,000 years ago or so and, again, with the migration of modern humans out of
Africa. "There's this history of a precarious existence not just for our species but for our ancestors," says
co-author Lynn Jorde, a human geneticist at the University of Utah in Salt Lake City.
Six degrees of separation.
Just 18,500 breeding human
ancestors were alive 1.2 million
years ago, even though they
had colonized much of the Old
World.
ADVERTISEMENT
Researchers have long known that modern humans lack the genetic variation found in other living
primates, such as chimpanzees or gorillas, even though our current population size is so much larger. One
CREDIT: GREG WAKABAYASHI
explanation for this lack of variation is that our species underwent recent bottlenecks--events where a
significant percentage were killed or otherwise prevented from reproducing. Some researchers proposed that the lack of variation in our
maternally inherited mitochondrial DNA suggested these bottlenecks took place as our ancestors spread out of Africa relatively recently. One
possibility occurred 70,000 years ago, when the Toba super-volcano erupted in Indonesia and triggered a nuclear winter that fewer than 15,000
individuals survived. Studies of diversity in other regions of the human genome, however, attributed low genetic variation to chronically low
numbers, with as few as 10,000 breeding humans at different times during the past 2 million years. But the problem with all these studies is that
they tracked specific genetic lineages, and not the entire genome and, hence, populations.
Now, a new method of studying markers across the entire genome is allowing geneticists to look back farther in time, before the emergence of
our species 200,000 years ago, to see the population history of our really ancient ancestors, such as Homo erectus. Jorde and his colleagues
used short lengths of DNA that randomly insert themselves into the genome, known as Alus, as probes to find ancient parts of the genome. Alu
insertions are rare events but once inserted, they are hard to remove--a 300-basepair-length of an Alu is seldom lost in entirety, so Alu
insertions work like fossils to mark ancient regions of the genome. By examining the mutations in DNA near Alu insertions in two completely
sequenced modern human genomes, they could calculate how much genetic diversity existed in our ancestors. They used the number of those
genetic differences between the two genomes to calculate how large the population was at that time.
As they report online this week in the Proceedings of the National Academy of Sciences, the researchers found that the ancient human effective
population size 1.2 million years ago, the number who could breed--was about 18,500, and couldn't have been larger than 26,000. This means
that even before the emergence of Homo sapiens in Africa, our ancestral population of Homo erectus was small even at a time that the species
was spreading around the world. This implies an "unusually small population size for a species spread across the entire Old World," the authors
write.
Population geneticists, including Montgomery Slatkin of the University of California, Berkeley, say that the theoretical analysis in the new
method "seems correct." The findings also "wonderfully illustrate how chance events, (such as the random insertion of Alus), have contributed
to patterns of human genetic variation," says population geneticist John Wakeley of Harvard University.
( skip to comments for this article )
Previous Article
Comments
Thanks for your feedback. Please keep it polite and to the point.
Echo 14 Items
Admin
To Advertise
Find Products
Doopylily
It sounds like a miracle that we are here on earth today.
Yesterday, 7:47:33 PM – Flag – Like – Reply
Guest
its amazing what might trigger a evolution or change in DNA. Im new to all this, yet im always fascinated by DNA, lineage, and genetics along with Geography.
Yesterday, 9:06:36 PM – Flag – Like – Reply
jwcornis
@Doopylily And what do you have to say to all of the other species that didn't make it. Aww, to bad. No one could have seen that that volcanic eruption/asteroid
impact/desertification of your habitat coming. It looked like you would last millions years longer. It's just a miracle that circumstances allowed your extinction.
http://sciencenow.sciencemag.org/cgi/content/full/2010/119/2?rss=1
1/20/2010
Human Ancestors Were an Endangered Species -- Gibbons 2010 (119): 2 -- ScienceNOW
Page 2 of 3
Life dies. period. Not a bad thing, but a good thing, just a thing. Given a slightly different set of circumstances, you and I would be the evolved descendants of
Neanderthals, or dinosaurs, or trilobites. If humanity wipes itself out tomorrow in several million years there might be another tool using, external memory storing
species that would develop it's own paleo-anthropology (or the equivalent) and look at how it was a miracle that their species made it.
This the way that life, generation after generation, eon after eon, has worked on Earth.
Definitely marvel in it, don't assign it a value.
Yesterday, 9:33:16 PM – Flag – Like – Reply
Liked by
Mkay
alfred warren
all this is good to know, so as a homosapien, this boogles the mind while at the same time lends support to cultures and its beginnings etc., veeerrrry
interesting!!!!
Yesterday, 10:23:19 PM – Flag – Like – Reply
Daniel Gutierrez
Ms. Gibbons,
Just a couple of comments on the grammar. The article’s grammar indicates the genome is the Alus, but the genome is not a short length of DNA. Grammar
should state first what the Alus: a short polynucleotide sequence that is inserted randomly into a genetic sequence (in this case, someone’s genome. Whose
genome was it anyways? And how old was it?). The genome must have been very modern given the high effort it took for the genome project to complete such
magnificent task. Wait, am I behind, did they also sequence the entire genome for Homo erectus? I would love to see this information next time you publish it.
It would also be helpful if you could help us understand more about the algorithms used to determine age (or timeframes)from “genetic variance resulting from
insertion mutations.”
Yesterday, 10:28:06 PM – Flag – Like – Reply
New Jersey
NEANDERTAL GENOMICS:
Tales of a Prehistoric Human Genome
Elizabeth Pennisi
After a mad scramble, researchers have completed a rough draft of a female Neandertal genome, which will offer a new view of Homo sapiens as well as
our extinct cousins.
Science 13 February 2009:
Vol. 323. no. 5916, pp. 866 - 871
DOI: 10.1126/science.323.5916.866
Today, 9:37:23 AM – Flag – Like – Reply
cardimom
The information coming from genome studies is just amazing.
Yesterday, 10:47:41 PM – Flag – Like – Reply
Dallas
Do you think that the extreme levels of geographic dispersion could have affected the breeding chances (and ultimately the birthrate) of these hominids. Even
assuming that homo erectus was probably not as picky as we are now, it could have impacted our population growth enormously.
I am not clear if h.erectus had an eustrus cycle or not, but such a situation would certain fastrack one into a menstral cycle instead if mates are hard to find.
Today, 2:07:49 AM – Flag – Like – Reply
Justin Schneiderman
I have a hard time following the reasoning behind extrapolating the effective population size at some point in the past from the present-day genome. Was
the "Mitochondrial Eve" really the only woman that could breed in her generation? I don't think that could be the case. I think our genome can only give
information about the numbers of ancestors that actually did breed successfully and whose progeny didn't die before they did the same, rather than saying
anything about those that could breed at any given moment. Of course, I'm not aware of the details of the analysis and therefore could very well be wrong.
Today, 6:18:37 AM – Flag – Like – Reply
smita jugale
if is it so then what should be effective population size for present era in homo sapiens?
Today, 7:16:40 AM – Flag – Like – Reply
terih2os
I think our ancestors were smart but were overcome by the elements and disease and those that survived had little to defend against predators. But it is those
that survive against all odds that overcome the most and are the most successful. It is time for us to look back and rescue that which we are destroying before
that is gone forever.
Today, 7:57:38 AM – Flag – Like – Reply
AlanB
If these studies are no more accurate than past ones I am led to doubt their credibility. Each study seems to contradict the last one and each asserts that it is
correct. Maybe the Earth really is flat!
Today, 8:32:53 AM – Flag – Like – Reply
dan stativa
I think that this study is clearly raising some new questions at least, if not responding to old ones. I am thinking more and more about creationism and
the "intellingent design" and how it will fit as a "scientific theory" with the real scientific discoveries of these next few years. Please tell me your opinion taking
this point of view.
http://www.anunturilazi.ro
Today, 10:09:57 AM – Flag – Like – Reply
http://sciencenow.sciencemag.org/cgi/content/full/2010/119/2?rss=1
1/20/2010
Human Ancestors Were an Endangered Species -- Gibbons 2010 (119): 2 -- ScienceNOW
Page 3 of 3
tadchem
This report is almost a tautology. Every living creature is a member of a species. Every species, during the period in which it is emerging, is extremely scarce and
thus at its most vulnerable - i.e. endangered. Thus, every living creature is a member of a once-endangered species. Only the successful species remain. Wa one
of the co-authors named "Captain Obvious?"
Today, 10:21:38 AM – Flag – Like – Reply
Social Networking by
From
To
Your name here...
This Page
What's on your mind...
Follow
Cancel
Post
News | Science Journals | Careers | Blogs and Communities | Multimedia | Collections | Help | Site Map | RSS
Subscribe | Feedback | Privacy / Legal | About Us | Advertise With Us | Contact Us
© 2010 American Association for the Advancement of Science. All Rights Reserved.
AAAS is a partner of HINARI, AGORA, PatientInform, CrossRef, and COUNTER.
http://sciencenow.sciencemag.org/cgi/content/full/2010/119/2?rss=1
1/20/2010