h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Not that I'm nitpicking, but the last time there was a supervolcano eruption was Mount Toba in Sumatra, aboput 75000 years ago. They reckon the total world population of humanoids at that time was about 1 million. After the eruption and the subsequent volcanic winter, there were about 5000 humanoids left. This accounts for an apparent "bottleneck" in our mitochondrial DNA, and explains why, after more than three million years of evolution, humanoids are still relatively lacking in genetic diversity.

In the book 'Science of Middle Earth', I just read about that lack of genetic diversity. I am glad to learn the reason for it...

Is it a certainty that the eruption 75000 years ago is the reason for the bottleneck in human diversity? I read something recently that said this is more or less an guess.
Anyone know for sure?

Nope!

C \|/

Is it possible to know for sure?

Not sure, no. But if the Toba eruption and the genetic bottleneck occur at the same time then it's a good bet.

Noggin

Yeah, but how certain is the dating of the bottleneck?

I believe that the dating of the volcanic winter is easy enough through simple geology, etc.. As to the genetic *bottleneck* I imagine it's just a logical assumption due to the harsh conditions the event would create. I suppose a *kill-off* of ninety five percent or so (excuse my bad math if I got that wong) makes sense.

The date of the genetic bottleneck was apparently reached quite independently of the geology, and was known before the date of the Toba eruption had been worked out. The genetic bottleneck was extrapolated backwards by the known rate of diversification of mitochondrial DNA. Or something along those lines, I believe.

C \|/

Ah, so does the geologic dating and the genetic dating relate at all? Fascinating stuff!

Chai
I used the 1000 amount at the time of Toba, because that was the figure used in the BBCs super volcano documentary. At the time I thought it was a very small population

I think the dating of Toba was discovered by layers of ash and massive amounts of animal bones in the strata.. again according to BBC documentary

Here's a picture of our gggggggggggggggggggggggggggggggrandmother

http://en.wikipedia.org/wiki/Mitochondrial_Eve

That's a really interesting piece on "Mitochondrial Eve" from Wikipedia. Here's a link to the original BBC Supervolcano documentary broadcast in 2000 which tells of the Mount Toba/DNA bottleneck:

http://www.bbc.co.uk/science/horizon/1999/supervolcanoes_script.shtml
The relevant section is near the end.

C \|/

Those were interesting links, but is the DNA evidence anything more than suggestive? It could well have been something else which caused the genetic bottleneck. As hyper-generalists, I think humans would have been better placed than most animals to deal with sudden climate change, so why don't other species show a similar bottleneck, especially those with a more limited geographical range (there is fossil evidence from South Africa and Israel from 90k years ago)?

Any thoughts?

Maybe there are similar bottlenecks within individual species that parallel the human one. Has anyone actually studied, say, the genetic diversity of pigeons worldwide to see if they should be more diverse than they are, or is there a 75,000 years hiatus in their DNA also? It's an interesting hypothesis.

Of course, the genetic disruption would primarily affect larger animals because of the devastating effects of volcanic winters on their foodchains. What would the effects have been on whales, for instance, and other sea-life dependent ultimately on light-dependent plankton? This is an interesting area, but all I can think of is more questions. Who has the answers?

Not me.
The only other studies I vaguely remember are one for cheetahs, saying they had a huge bottleneck (but I've no idea about the timing), and one for chimps saying that as a species they're at least 1 million years old.
But I would imagine this genetic bottleneck should show up for many animals, not just us.

Presumably the bottleneck should show up for all animals affected by the volcanic winter. And of course there may be species that went extinct that we don't know of because their fossils/remains haven't been found or recognised. Presumably also there should be a genetic bottleneck within the chimpanzees' mitochondrial DNA too. After all, it's not that humans aren't old as a species ( about 3 million years or so as hominids ), but that we're not as diverse as our species age would predict.

Actually humans as a species are thought to be much younger than that - probably about 150-200 thousand years.

Noggin