Humans were once an endangered species

Jan 21, 2010 by Lin Edwards report
Temporal and Geographical Distribution of Hominid Populations Redrawn from Stringer (2003). From: Genetic Analysis of Lice Supports Direct Contact between Modern and Archaic Humans Reed DL, Smith VS, Hammond SL, Rogers AR, Clayton DH PLoS Biology Vol. 2, No. 11, e340 doi:10.1371/journal.pbio.0020340. Image via Wikipedia.

(PhysOrg.com) -- Scientists from the University of Utah in Salt Lake City in the U.S. have calculated that 1.2 million years ago, at a time when our ancestors were spreading through Africa, Europe and Asia, there were probably only around 18,500 individuals capable of breeding (and no more than 26,000). This made them an endangered species with a smaller population than today’s species such as gorillas (approximately 25,000 breeding individuals) and chimpanzees (an estimated 21,000). They remained an endangered species for around one million years.

Modern humans are known to have less than other living primates, even though our current population is many orders of magnitude greater. Researchers studying specific genetic lineages have proposed a number of explanations for this, such as recent "bottlenecks", which are events in which a significant proportion of the population is killed or prevented from reproducing. One such event was the Toba super-volcano in Indonesia that erupted around 70,000 years ago, triggering a nuclear winter. Only an estimated 15,000 humans are thought to have survived. Another explanation is that the numbers of humans and our ancestors were chronically low throughout the last two million years, sometimes with only 10,000 breeding individuals surviving.

The new research is concerned with the entire genome rather than specific genetic lineages studied in the earlier research work. Using a new method of studying genetic markers of DNA in the genome has allowed geneticists to study the genetics not only , but also our early ancestors such as (thought the most likely to be our direct ancestors), H. ergaster and archaic H. sapiens. Remarkably, they found there was enough information in only two human DNA sequences to estimate the ancient population size.

Human geneticist Lynn B. Jorde and colleagues studied parts of the genome containing mobile elements called Alu sequences, which are sections of DNA around 300 base-pairs long that randomly insert themselves into the genome. This is a rare occurrence, but once inserted, they tend to stay in place over generations, and act as markers, rather like fossils, for ancient parts of the genome. On average, regions containing Alu insertions are older than other regions, and because they are old these regions have been shaped more by the forces that applied to ancient populations than to recent bottlenecks (such as Toba) and expansions.

The researchers studied mutations in the DNA near these Alu markers in two modern human genomes that have been completely sequenced. Older regions containing Alu sequences have more mutations because they have been in existence longer, and the researchers used the nucleotide diversity to estimate the age of the region of the genome. They then compared these regions with the overall diversity in the two genomes to estimate the differences in effective population size, and thus the genetic diversity between modern humans and our ancestors.

From these studies, they calculated there was more genetic diversity in our early ancestors than there is in modern humans. They also came to the conclusion that there had been a catastrophic event around one million years ago that was at least as devastating as the Toba volcanic eruption, and which had almost wiped out the species.

Jorde said that humans and our ancestors have gone through cycles of large population size and also periods when we were endangered. Professor Jorde and his team’s findings were reported online in PNAS, the Proceedings of the National Academy of Sciences on January 19.

Explore further: Rock-paper-scissors model helps researchers demonstrate benefits of high mutation rates

More information: Mobile elements reveal small population size in the ancient ancestors of Homo sapiens, PNAS, DOI:10.1073/pnas.0909000107

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jonnyboy
2.3 / 5 (6) Jan 21, 2010
A little too much if-ing, suppose-ing and out right guess-ing for my tastes but the chart does a fantastic job of showing the evolution, distribution and overlap of the various hominids.
vit
3.3 / 5 (8) Jan 21, 2010
I wonder why these disasters endangered humans, lowering our genetic diversity, but didn't do the same to most other animals.
DozerIAm
3 / 5 (4) Jan 21, 2010
Vit - what makes you think it didn't?
jsovine
1.7 / 5 (11) Jan 21, 2010
If you believe in the biblical flood, the population was reduced to eight persons at one point.
Nik_2213
3.7 / 5 (6) Jan 21, 2010
Toba's mega-eruption is in the sediment record and others, eg proto-Krakatoa or Yellowstone, will have erupted likewise. There's probably a bunch of candidates for that million-year choke-point...
===
"If you believe in the biblical flood..."

Let's not go there, please ??
thales
4.2 / 5 (5) Jan 21, 2010
The biblical flood has as evidence the deposition of large boulder sized rocks in the midst of thick and very widespread (hundreds of miles) of sedimentary rock deposits. Yeah, I wish the biblical narrative was more exact and detailed, but the rock strata is(are) there to see.


Link? Reference? Since this is apparently easily seen, there must be documentation.
panorama
4 / 5 (8) Jan 21, 2010
If you believe in the biblical flood, the population was reduced to eight persons at one point.


So we're all inbred cousins of each other? Mythology is fun, but let's leave it out of our Science.
Phelankell
2.6 / 5 (5) Jan 21, 2010
Interesting research, however, how can we say anything to that effect when our fossil record is so thin and unsubstantiated for homonids. Perhaps there were not many changes because the changes the species underwent at the time were highly deleterious. That is about the same time we began a massive retrofit of our locomotion and other habits.

mark0101
not rated yet Jan 21, 2010
Vit - what makes you think it didn't?


Judging by the distribution chart, you can see it didn't effect them as much as it did us
EndlessFormsMstBeautiful
5 / 5 (3) Jan 21, 2010
I find it too difficult to believe that we came from apes...


We did not "come from apes". We share a common ancestor, but did not evolve from them.
Parsec
4 / 5 (4) Jan 21, 2010
A bottleneck of 8 persons at any point in the existence of our species would not only have a 99% chance of wiping out the species altogether because of extreme inbreeding, but would also be VERY detectable by a variety of other methods (our genetic diversity would be almost zilch... we would basically all look alike). So it is quite safe to conclude that we have never experienced that catastrophe. Even 11k individuals put our population at high risk because of the inevitable inbreeding.
Parsec
3.7 / 5 (6) Jan 21, 2010
Note also that this study did not look at any 'fossil' evidence, other than that contained in our genetic record. So there is no need to worry about the fossil record, whither or not you believe in evolution, etc. Of course, if you believe that the earth and all its creatures are around 800 years old there is a conflict. I wouldn't worry about it tho, since that belief makes 90+% of all scientific results in every field totally bogus.

Of course, if scientists are all agents of Satan whose entire mission is to destroy the faith of the true believers, that is a plausible, if highly unlikely, world view.
Phelankell
1 / 5 (3) Jan 21, 2010
Off course, myself/defunctdiety/vellanaris all being the same also makes any intelligent conversation highly unlikely in any conversation.

I believe you made a mistake and meant "veianarris"/"pheiankell"/and "defunctdiety_"

Don't worry, the moderators will catch up with you shortly.

Now back to the actual discussion, Parsec, I understand they didn't look at physical fossils, however, it's a huge assumption to assume greater genetic diversity prior to the bottleneck without an in depth analysis of a significant number of pre-bottleneck fossils. It's quite possible the species went through a lull in mutation, or a period of mutation with few favorable outcomes as we've seen in some other species.
Caliban
1 / 5 (2) Jan 21, 2010
Unfortunately, due to the total lack of any viable DNA in fossils of more than a few tens of thousands of years old- that is a question that will remain unanswered. Don't really have any choice but to assume a much greater degree of variation, as is observed in most other species.
Also, it bears noting here, I think, that if these "bottlenecks" are actually the case, then that would also reinforce the case for the relative paucity of homimid fossils in the record, would it not?
ekim
3 / 5 (2) Jan 21, 2010
Considering that a nuclear winter had nearly caused the extinction of our species, might I offer a solution that does not involve sticking our heads in the sand or praying to a higher power.
Termite farming.
Termites eat cellulose, other animals, including ourselves, could eat them. There is enough cellulose stockpiled on this planet to last our species a long time. Wood, warmth, and water would be all that they would require. All we would need would be a large enough bucket, and maybe some chickens.
Phelankell
2.6 / 5 (5) Jan 21, 2010
Termite farming.
Except termites are far worse for the planet than cows, in addition to being toxic in their production of ethylene gas when threatened.
PinkElephant
not rated yet Jan 21, 2010
I don't understand the study's methodology, at least as represented in the physorg blurb. So, they looked at Alu segments and judged how old they were by counting accumulated mutations therein. But how on earth does that tell them anything regarding the recent history of DNA adjacent to Alu? And how on earth do they judge DNA next to an Alu as "old" vs. "new" otherwise?

Example: Gene A - Alu - Gene B. Let's say Gene A had a major mutation 5 million years ago. Then, 1 million years ago, Alu was inserted between A and B. Then, 1 century ago Gene B nad a major mutation. According to the study, both Gene A and Gene B are "old" because they're close to an Alu sequence. What gives???
ekim
not rated yet Jan 22, 2010
Termite farming.
Except termites are far worse for the planet than cows, in addition to being toxic in their production of ethylene gas when threatened.

They also would produce methane along with the ethylene. Why would you let these gasses escape the bucket when they could be captured? Also, we won't care about the planet if we're not alive to care about it. Worrying about global warming during a nuclear winter?
Parsec
3.7 / 5 (3) Jan 22, 2010
Actually genetic diversity is pretty easy to determine across a species, and its pretty easy to see how close the entire genome of individuals are separated.

In this study they used the variability of Alu region insertion times to find the genetic diversity at specified times. If the genetic diversity of is highly limited in Alu regions that were inserted at or around a specific time, then you the genetic diversity at that time must have been low.

I think this study is brilliant because they managed to make these measurements without having to look at pre-bottleneck fossils, or in fact any fossil sequences at all. You have to read the original article to see it, but I have seldom seen such startling results with reasonably low error bars without considering the data I would personally (as do most of the commenter's here) would have considered essential. But the results are real, and the arguments quite persuasive.
VeIanarris
3.7 / 5 (3) Jan 22, 2010
Termite farming.
Except termites are far worse for the planet than cows, in addition to being toxic in their production of ethylene gas when threatened.

You seem to forget that termites are a delicacy in many parts of Africa, when the mating flights occur and he insects are atracted to flames the feasting starts!
Californiasteven
not rated yet Jan 23, 2010
Has anyone considered that when people became intellectually aware that sex leads to pregnacy that could have been a crisis?
Shootist
3 / 5 (2) Jan 24, 2010
"They also came to the conclusion that there had been a catastrophic event around one million years ago that was at least as devastating as the Toba volcanic eruption, and which had almost wiped out the species."

A quick preview of the Impact Database v.2009.2 (http://impacts.ra...ta.html) shows the following confirmed, million year old, impact events;

New Quebec, Canada 3.4km 1.4+-.1 Ma
Zhamanshin, Kazakhstan 14km .9+-.1 Ma
Bosumtwi, Ghana 24km 1.07 Ma

Of the three, Bosumtwi would have delivered to the surface of the planet >3.7x10^20 Joules. or about 90000 megaton of TNT equivalent.

French B. M. (1998) Traces of Catastrophe: A Handbook of Shock-Metamorphic Effects in Terrestrial Meteorite
Impact Structures. LPI Contribution No. 954, Lunar and Planetary Institute, Houston. 120 pp.

Quantum_Conundrum
3 / 5 (2) Jan 24, 2010


So we're all inbred cousins of each other? Mythology is fun, but let's leave it out of our Science.


Even discovery channel found that every human is 99.9% identical to every other human genetically.

I once calculated that pre-historic humans could have been exponentially more genetically diverse than modern humans, but have the same number of total Chromosomes, and still be sexually compatible with modern humans.

So yes, every person on earth today is decended from literally a handful of people expressing at most a few hundredths of the original genetic diversity (presumably before the Flood).

You also have to remember all the wars genocides throughout history and pre-history

With no bottleneck, Adam and Eve could have had as many as 6.6408*10^20 genetically unique offspring (children, grandchildren, etc.)....without mutation...Assuming they were created with maximum compatible chromosomal diversity.

Shootist
1 / 5 (1) Jan 24, 2010

With no bottleneck, Adam and Eve could have had as many as 6.6408*10^20 genetically unique offspring (children, grandchildren, etc.)....without mutation...Assuming they were created with maximum compatible chromosomal diversity.


But who did Cain inseminate? What with Abel dead and all . . .
Birger
5 / 5 (1) Jan 25, 2010
Something called "mutational meltdown" can finish off a species if it is reduced to a few thousand individuals. This is because mildly deleterious genes will not be removed from the gene pool as efficiently as with a large population. Apparently, our ancestors came close to the size limit...
Skeptic_Heretic
not rated yet Jan 25, 2010
With no bottleneck, Adam and Eve could have had as many as 6.6408*10^20 genetically unique offspring (children, grandchildren, etc.)....without mutation...Assuming they were created with maximum compatible chromosomal diversity.


Yes but that is assuming no deleterious mutations, no fertility nullifying mutations, and then you're not speaking to the following generation that would produce NO unique individuals as they would all be repeats of the originating pair.

2 humans could produce several generations, but not much further as the mutations would have to outpace procreation, and that's not possible.
damnfuct
not rated yet Jan 25, 2010
What is more interesting is that that such "detrimental" genetic bottlenecking would produce a species that could thrive while two other similar ones went extinct; perhaps some "fat" got trimmed.
Skeptic_Heretic
5 / 5 (1) Jan 25, 2010
What is more interesting is that that such "detrimental" genetic bottlenecking would produce a species that could thrive while two other similar ones went extinct; perhaps some "fat" got trimmed.

Evolution tells us otherwise.
The most suited to adapt to the current environment will always thrive unless acted upon by forces that directly affect that survival.

Very well could have been disease that wiped these people out while these surviving individuals were geographically isolated from other humans. Could also have been that they shared a single factor immunity. There just isn't enough evidence either way.
mrlewish
not rated yet Jan 26, 2010
Once? I think they will be again one day if the path we are on doesn't change.

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