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Humans Nearly Went Extinct 1.2M Years Ago
Hugh Pickens writes "Scientific American has a story on researchers from the University of Utah who have calculated that 1.2 million years ago, at a time when our ancestors Homo erectus, H. ergaster, and archaic H. sapiens were spreading through Africa, Europe, and Asia, there were probably only about 18,500 individuals capable of breeding in all these species together (PNAS paper here). Pre-humans were an endangered species with a smaller population than today's gorillas and chimpanzees. Researchers scanned two completely sequenced modern human genomes for a type of mobile element called Alu sequences, 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. Human geneticist Lynn Jorde says that the diminished genetic diversity one million years ago suggests human ancestors experienced a catastrophic event at that time as devastating as the Toba super-volcano in Indonesia that triggered a nuclear winter and is thought to have nearly annihilated humans 70,000 years ago."
The end result is the same as that predicted for nuclear winter. Radiation is not the primary danger from a "real" nuclear winter, it's the smoke and soot that would spread through the atmosphere, drastically reducing the amount of sunlight received at the surface, killing plants and reducing temperatures everywhere. When a supervolcano goes off, the effects are nearly identical.
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The 18500 people quoted is not the number of people capable of breeding, but the "effective population", an abstract measure of genetic diversity in a species. According to TFA, the effective population of modern humanity is about 10000, and the argument in the article is that this much lower diversity indicates that a lot of genetic material must have been lost in a near-extinction event.
Aight, Bloodninja was his name!
But why should we assume a uniform rate over time, when evolutionary theory says that genetic differentiation happens in leaps and bounds?
See, here is your problem, you're assuming evolutionary theory is correct to begin with.
Indeed, much of science is based on a giant leap of faith in linear regression; physicists, chemists, doctors, engineers, all use linear regression without questioning its assumptions.
No, they use linear regression and then test to prove it's a reasonable assumption.
What happened to those? Sounds like an excellent power source...
http://en.wikipedia.org/wiki/Geothermal_gradient
"The Earth's internal heat comes from a combination of residual heat from planetary accretion (about 20%) and heat produced through radioactive decay (80%)"
In a sense, those "green geothermal" power plants are really nuclear power plants.
"Science flies us to the moon. Religion flies us into buildings." - Victor Stenger
The proper description would be volcanic winter.
You can find just about any belief "in some societies" if you look hard enough. The reality though is that in the English language the words brother and sister have a specific meaning: persons who share at least 1 biological parent. Some relatives from millions of years ago don't count.
Besides, from a biological standpoint, once you're to the genetic "distance" of only first cousins (1/8th DNA in common) the chance of birth defects drops off to the point of being completely fine. Indeed "in some cultures" marriages between cousins is very common (heck even in the US with all the attached stigma it's still perfectly legal for cousins to marry in most states). Thinking "we're all related man!" is only a problem from the standpoint of cultural taboo. Beyond the very immediate family it's not a problem.
"People who think they know everything are very annoying to those of us who do."-Mark Twain
First cousins have a common ancestor two generations back. So 53rd cousins should have a common ancestor 54 generations back.
54 generations ago, you had (theoretically) 2^54 ancestors (~180,000 trillion). Which means that statistically speaking, every human alive ~1200 years ago was about 200,000,000 of your ancestors.
In other words, such a number is pretty much meaningless....
"I do not agree with what you say, but I will defend to the death your right to say it"
Of course, when the range between eruptions is 660K to 800K, the low end of that would still make it another 20K years before the next eruption, or roughly twice the entire length of the history of human civilization. "About due" in geological time is very different from most people's view of "about due".
Yes, I'm aware the eruption could come earlier than previously observed, but it's not really worth worrying about events with astronomical odds that you can do nothing about now is it?
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Or they could have just said 'volcanic winter' like the Wikipedia page they link to.
We also have written evidence that Frodo set forth from the Shire in order to destroy the One Ring before it fell into the hands of Sauron. But so what?