Have Humans Come Close To Extinction?

waytoomuchcoffee writes "According to a new study, our virtually identical DNA indicates humans were close to extinction about 70,000 years ago. Another take on the same study tells how being lactose intolerant in adulthood was normal, and being able to digest lactose became a survival advantage after dairy farming was invented."

Comments

Diversity in a small group

[Inexile2002]

Unlike our close genetic relatives - chimps - all humans have virtually identical DNA. In fact, one group of chimps can have more genetic diversity than all of the six billion humans alive today.

Something about that struck me. If the natural state of affairs is for a wide genetic diversity even in a small group - such as the chimps, then why wasn't there a similar diversity in the 2000 people who went on to sire the rest of us.

Think about it. A chimp troop can consist of up to 60-70 chimps for a big troop. Assume all but around 30 troops are killed off leaving around 2000 chimps. If a single troop of those chimps could have more genetic diversity than all of humanity - ie. more than the 2000 people who sired us then 2000 chimps would have around 30 times more diversity. (Or more than that depending on how much more diversity in a chimp troop than there is in humanity.)

So, either humanity dwindled down by chance to 2000 people who happened to have little genetic diversity, or there was some common genetic trait that selected for those specific people. Or something. But then who knows... maybe chimps are just naturally genetically diverse and we're not... or maybe I just missed something that the writer thought was too technical for the article.

Still, the numbers bothered me.

Re:Diversity in a small group

[AllenChristopher]

And moreover, when that little group discovers something like the hatchet, they suddenly outcompete everything that eats the same food as them, but isn't in the tribe and isn't told the secret. Time and again, one tribe wipes out all the tribes nearby with a new weapon or other new technology, thinning the gene pool.

In the 1300s, there certainly weren't a billion people of European descent. There were more like 50 million. That's barely thirty generations ago. This sort of thing happened in pre-history as well.

Re:Diversity in a small group

[aug24]

What you are missing, I think, is that diversity reduces in small total populations.

Chimps, can and do change troops, interbreed with other troops, exist as lone males, etc. If they were reduced to 2000 or so then they would not maintain their current level of genetic diversity as, for example, fewer males would have the opportunity of siring offspring.

Hence it is not a like-for-like comparison. You are comparing pre-small-pool chimps with post-small-pool humans. Although given the state of the world's primates, it won't be long before you can make the comparison fairly :(

J.

Re:Diversity in a small group

[EvilTwinSkippy]

Just look in the Bible. (I'm a secularist myself, but the old testimate is an entertaining folk tale.) How many Son's did Abraham have? You have Lot who had a lot of kids by his daughters. I mean incest, polygamy on a mass scale, all the makings of a really shallow gene pool.

Then you have Kings from other cultures who would spread their seed wide and far. You see the same behavior in rock stars and sports figures today. How many kids did Jim Morrison sire? How about Wilt Chamberlin? Hell even Ben Franklin got around. In every cult what happens? The cult leader fucks all the groupies.

Women are drawn to success. Men are drawn to breed with healthy women. In less enlightened times someone Enronized our Gene pool by being really successful and not being dumb enough to die young before they spread.

Re:Diversity in a small group

[Muad'Dave]

Unlike our close genetic relatives - chimps - all humans have virtually identical DNA. In fact, one group of chimps can have more genetic diversity than all of the six billion humans alive today.

Why doesn't such impressive genetic diversity in the chimp world translate to more obvious facial/structural diversity as is seen in the wildly differing appearances of humans?

To put it another way, if they're so genetically diverse, why do they all look alike? I'm sure Jane Goodall, et al, can tell different troops and individuals apart, but I sure can't. Perhaps chimps think we all look the same, huh?

Additional Comments on reflection

[Inexile2002]

Thinking about that, I didn't make myself clear on something. What I was trying to say was that if a single troop of 60 to 70 chimps can have X diversity, shouldn't a group of 60 to 70 humans - a close relative of the chimp - also have X diversity. What struck me about the article is that their implication is that those 2000 people they say sired us had less diversity than 60 to 70 chimps.

Makes you wonder if it has something to do with human females being fertile year round. If I recall, chimp females are not. Because chimps can only mate at certain times, there is less oppurtunity for one male to sire all the children in a troop. In a human harem type social group, this could be easily accomplished which would cut down the genetic diversity considerably. Do this for a couple of generations and you might end up with a population with a depressed gene pool. Anyway, just arm chair theorizing off the top of my head. (Gotta use that anth degree for something.)

Re:Additional Comments on reflection

[zenyu]

Makes you wonder if it has something to do with human females being fertile year round. If I recall, chimp females are not. Because chimps can only mate at certain times, there is less oppurtunity for one male to sire all the children in a troop.

I think the article isn't specific enough to judge whether sexual practices have anything to do with it. Pygmy Chimps (Bonobos) always look like they are in heat and like humans who never look like they are fertive have sex with anything that moves. But most chimps have a stratified society where only one male at a time has sex with all the females. The females do cheat on him, but I don't know how common those children are. Even the Amish have plenty of out of 'falsely fathered' children so I don't think humans should be less diverse due to sexual exclusivity.

More likely there where several rounds of near human extinction and just the latest one was sometime in the last 100,000 years. We also have this nasty habit as a species to eat those that aren't 100% human...perhaps our competitors had similar tastes ;) (JK! -- no homo erectus, homo neanderthalis hate mail pls)

Re:Additional Comments on reflection

[maxume]

One thing that might be a factor that you don't seem to have mentioned is that most chimps are probably under considerably higher environmental pressure than the average human. The genetic makeup of todays typical human doesn't really have all that much to do with the continuation of his genetic line. It seems like the increased pressure for selection in the chimps would cause them to evolve faster than humans do. I don't really mean evolve in the sense of becoming greater as a species, but in the sense of becoming better suited to a particular environment.

If two sub groups of chimps each evolved under rather disparate conditions, and then crossbred, it would seem that their genetic diversity would increase. Considering that we as humans don't really evolve to any particlar environment anymore(we move around way to much), and we crossbreed pretty much constantly, perhaps the chimps are just doing a good job of playing survival of the fittest?

Re:Additional Comments on reflection

[Martin Spamer]

Your first post was pretty clear and interesting question.

A prolonged & extreme selective pressure is a cause of reduced diversity. An obvious candidate must be the last Ice-Age which also fits nicely into the time frame. This issue has recently been covered in a excellent BBC documentary series Walking with Cavemen, which also featured a figure of 2000 females in a significantly reduced human population. I suspect the last programme was based at least partly on this research.

The programme suggested that until the Ice Age human 'tribes' where extended family size (~12) but survival in the Ice-Age was linked with a strong selective pressure for larger groups (~200). Socialisation allowed specialisation and increased expertise, this allowed food shortages to be more readily smoothed out. Socialisation and Specialisation both required elevated intelligence.

A idea to consider is that the number of people could have been larger than the 2000 suggested but the genetic heritage of the extras doesn't survive today; consider the effect of evolutionary shock caused by the large group coming into contact with smaller groups, the larger would quickly swamp the genetics of the smaller group. The larger group would be more genetically diverse than the smaller group and more resistant as a group to any diseases pool.

Also consider the negative impact on genetic diversity of plagues and pandemics, Influenza, Small Pox, Cholera, Black Death, many of these have surely sweep the world before recorded history leaving only immune populations, and reducing diversity.

Re:Additional Comments on reflection

[kmilani2134]

The interesting thing is that scientists have found that chimps (I believe what I saw was about the Bonobos) have two different types of sperm. Half the sperm actually serve the purpose of forming a sperm "wall" or barrier to keep other monkey's sperm from reaching the females egg.

I guess it pays to be first.

Close to Extinction?

[Sunlighter]

Arguably, in spite of our numbers, we're close to extinction now.

Hey, good to know we got out of it last time.

Dogs

[Beryllium Sphere(tm)]

Robert K. Wayne of UCLA has estimated that we may have domesticated wolves as much as 100,000 years ago.

What if it was 70,00 years ago? Did our partnership with dogs save our species?

Re:What a liability for humans!

[yarbo]

sounds like the setup for Geek Love. A circus family that intentionally tried to produce freaks for their show. It was an excellent book.

Noah's ark

[DJ Rubbie]

Could the biblical story of Noah's ark explain this, as a worldwide flood leaving only a single family of eight alive will achieve this effect of everyone having similar genes.

Before you mod me down into oblivion for sounding like a self-righteous Creationist, do note that other cultures have references to a catastrophical flood (such as the Chinese, apparently the character for ship is that story).

Re:Noah's ark

[MonkeyDluffy]

No.

There is no evidence whatsoever that there was a worldwide flood - and a disaster of that magnitude would leave lots of evidence. And nobody told the Egyptians and Chinese about it - their civilizations were going strong before, during, and after when the flood supposedly occurred.

Many cultures have flood stories, because towns are usually located near good water supplies such as lakes and rivers. Which flood on occasion.

-MDL

Wacko Sci-Fi Theory

[EvilTwinSkippy]

Perhaps humans haven't always lived here. Think about it, most cultures have an Atlantis-like legend, and a Flood/Migration legend.

Could it be possible that we are the decendents from a crashed spacecraft? Maybe I played Homeworld too often, but doesn't it seem funny that we are the only primates that can:

• Swim
• Choke to death on food (Apes and monkeys can breathe and drink at the same time.)
• Lose our Virginity.
• Cry

(A great site that goes into more detail is: Here.)

At times we have more anatomically in common with a Seal than an ape. Not enough to make me buy a tinfoil cap, but precisely how does an otherwise aquatic creature "evolve" on an Savanna, and then ddevelop their first civilization in the middle of a desert?

Re:Wacko Sci-Fi Theory

[EvilTwinSkippy]

Now you have to ask yourself: how?

I realize that all of these traits are probably dormant in all mammals, and were simply re-expressed in humans through mutation. The enlarged forehead of humans is actually a common feature of infant apes, our forehead simply doesn't receed during maturity. (Though you wouldn't know it looking at the behavior of some people.)

But there is a big problem. We somehow successfully mutated several major features in our Genome in the blink of an eye. To boot, we did it with a relatively small gene pool. Granted, the two could aggrivate each other.

Something REALLY wierd happend at some point in our developmental past. In the absence of any records, fossils, or talking ghosts just about any answer is good.

Re:Wacko Sci-Fi Theory

[OpenSourced]

For a possible (rather reasonable) explanation, read "The descent of woman" by Elaine Morgan. She theorizes that human beings are part acuatic, that part of our evolution happened at sea, or rather at the coast making extensive use of the sea. That explains the biped position (to walk into sea as far as possible), the hairlessness (you drop hair as a thermo insulator and get fat instead if you know what's good for you, when you are at sea), the big nose with downward-pointing holes, the crying (eliminates salt by being more saline than normal fluids), and, although she doesn't mention it, the fact that you cannot run faster than a dog, but sure can you swim faster. She made a convincing argument.

BBC should check it's own archives...

[EvilSuggestions]

I don't expect the BBC to do an exhaustive search of all the peer review journals every time they do a science story, but they should at least check their own archives to help explain an curious conundrum like this one.

The date given for the bottleneck, ~70,000 years ago, coincides perfectly with the largest volcanic explosion in the last half million years. One that spewed thousands of times as much ash as produced in the 1980 Mt. St. Helens eruption.

The explosion of Toba in Indonedia around 74,000 years ago probably caused a greater than 5 degree drop in average global temperature that lasted over 6 years. 5 degrees may not seem like much but that global average may translate to over a 15C drop in the summertime temperatures in the temperate regions and would have devestating effects on many of the plants we relied on for food.

Point is that most of what I just mentioned (and much more) can be found in a few articles on their own web site:

• Humans came close to extinction (1998)

  A new hypothesis about recent human evolution suggests that we came very close to extinction because of a "volcanic winter" that occurred 71,000 years ago.

  That article discusses a bottleneck of perhaps 15,000 humans. So the only real news is that the estimate of the bottleneck has been cranked back by an order of magnitude.
• BBC Horizon - Supervolcanoes (1999/2000)
• Supervolcanoes could trigger global freeze (2000)
• Walking with Cavemen (2003)

Big Volcanic blast ~70K yrs. ago?

[budalite]

This "news" is pretty old. There was even a Learning Channel (or Discovery) show a couple of years ago about the idea of "supervolcanoes", one of which could rest beneath Yellowstone and one (Toba) that, they think, blasted ~70K years ago, causing global average temperatures to drop and nearly causing our species to become extinct. Interesting stuff.

That would be the Masai. (admittedly -partly -OT)

[SolemnDragon]

And on the subject of the Masai, cattle are sacred to them, a gift from the god(s), and they generally don't kill them. In fact, they gave the USA fourteen cows in the wake of 9/11- a collective donation from many tribes, and (for them) a priceless gift. Our ambassador refused to accept it.

I don't know what happened to the cows. I do know that the Masai do, indeed, drink blood and milk mixtures. Having lived with a Jewish roommate, i can remember the look of horror on her face as she tried to interpret it into kosher food concepts.

Lactose Intolerance is not the only intolerance out there... Gluten intolerance hits 7% of the population (including me.) More women than men, mostly northern european descent. Me with my scottish pale skin and my german grey eyes, it's got my grandmum, my mum, my sister, and me. Skipped both brothers.

Part of my point being - there are genetic variations that are gender specific, there are genetic variations that are region-specific, and there are genetic variations that we're only just discovering. Another part of my point being- Lactose intolerance is unbelievably common. And i miss ice cream and milk. Lactase tablets aren't enough for a lot of people out there, that's how severe we're talking... I think maybe there are a number of changes that happened regionally, and now we're seeing the results as cultures blend. My dentist talked about it all the time, how asian teeth and african teeth and european teeth are similar but jawlines differ, and when you get different genes kicking in for jawbone and teeth it sometimes leads to really good combinations and sometimes leads to surgical correction so that the kid can chew. He said this in a completely nonracist way; he thought it was a great idea to blend genetic and cultural groups together, so he was more than happy to help correct the results of problem combinations, because they could usually be helped and their appearance meant that new combinations were always being created.

Oh, and about the Masai. Don't mess with a people who kill lions by hand. These are the people from the movie the ghost and the darkness- flushing out lions by shouting and beating the brush...

Toba

[4of12]

I'm surprised that article didn't pick up on the theory that the bottleneck in the genetic line about 70K years ago might well have been due to the eruption of the Toba supervolcano that was regarded as one of the most significant eruptions in the last 2 million years. That kind of climatic change from such an eruption could well be responsible.

Re:Jesus Christ...

[arkane1234]

Lactose intolerancy is a little bit more than just some farts... it's not like eating chili or something :)

It can really mess your day up... the major side effect of lactose intolerance is massive gastrointestinal issues stemming from the lactose not being broken down. I have it, and believe me it's not just gas or I could definately handle that.

Goats, not cows

[Tablizer]

Why didn't they domesticate goats for milk production instead of cows? Goats don't produce lactose in their milk. We can't easily switch now because goat milk tastes too different from cow's milk. We are too used to the taste. Cow milk is kind of like the QWERTY of milk.

you can so quantify diversity!!!!

[Anonymous Coward]

If geneticists needed to discuss gene diversity in some sort of quantifiable measure, it would eliminate their ability to discuss relevant topics. Unless you are referring to a specific sample of genes, you can't quantify the diversity.

Leave it to an anthro major to pull out bullshit like that.

Meanwhile, in the scientifc world, diversity has a specific technical meaning that can be measured using "H," or entropy, from Claude Shannon's information theory -- which is similar the measure of entroy in physics.

H(p) = - sum[i=1..X] (pi * log pi)

Just take Shannon's equation, plug in allele frequencies for the population (maybe use log base 4 for 4 base pairs?) and presto, a quantity of diversity