Evolution Of Humans In The Last Hundred Years.

My internet access is limited whimsically by our corporate servers so I'll have to get back to you when I find a reference. However, the report I read said that the median age of adult Paleolithic skeletons was around 52 years.

Obviously if you include children at any time before the modern era, when infant mortality was as high as 80%, human life expectancy would be abysmal. Which makes it all the more remarkable that, even calculated this way, the life expectancy at the zenith of the Roman Empire was only about 23.

The anthropologists who were examining those hunter-gatherer skeletons with modern instruments, finding evidence that was invisible to their predecessors, also discovered that more than half of those dead adults had been killed by other humans. In other words, not only was human-on-human violence the leading cause of adult death, it killed more adults than all other causes combined. This is consistent with your observation of the few remaining Paleolithic tribes.

I suppose the way to interpret this is to suggest that their lives were so healthy, with top-notch nutrition from a meat-intensive diet, immunities to the local pathogens bred through natural selection, an easy life (it's been calculated that since they had very little to do except find food, an activity at which they were experts, they had a twenty-hour "work week"), and the low-stress environment of a close-knit extended family, that they might live almost as long as we do if somebody didn't come along and whack 'em.

During the inevitable famines, clans would invade each other's territory after they ate all the game animals in their own, and a battle would ensue. Certainly the older people would be the first ones killed. Once they had each killed off the elders of the other's tribes they might have paused and said, "Hmm, I guess now there's enough food to go around so we can stop fighting."

It's ironic that today, at least here in the USA, human violence is one of the top five causes of death, but only for adolescents.

The pressures of the outside world on the Amazon tribes must be devastating. Since they can't kill the foreigners inside their metal bulldozers they probably vent their frustrations on each other.

But that's what a genetic bottleneck is. She is our only female ancestor in that generation. Indeed there may have been other women alive at the time, but if they had children none of their female bloodlines survived long enough to hybridize back into mt Eve's. Mitochondrial DNA is passed down only from the mother. This is why all human mitochondria are hers. There was no "other DNA" to be contributed "in subsequent generations." If there were other mitochondrial DNA, some of us would have it.

The same is true of Y-Chromosome Adam. He is our only male ancestor in that generation and all human Y-chromosomes are his. Again, other males in his generation may have had progeny for a couple of generations, but their bloodlines died out before they interbred with Adam's.

Y-Chromosome Adam was only a bottleneck on the male side, because only males have a Y chromosome. If there were women alive who did not carry mt Eve's mitochondrial DNA, it's statistically likely that Adam or some of his male children would have mated with them, and their daughters would have kept it alive.

Huh??? I've read six or eight different consistent accounts of this. Mt Eve lived sometime between 200 and 120KYA and Yc Adam lived between 90 and 60KYA. This would place him before the diaspora out of Africa, after which there could have been no species-wide genetic bottleneck.

Just start with their Wikipedia articles.

Well I suppose from a purely logical standpoint that would be a true statement, but it downplays the importance of Yc Adam. Besides, in this scenario both Adam and Eve had other mates available and monogamy is an implicit element of the story.

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We know that he lived at least thirty thousand years later than Eve, and more likely sixty.

 

Mathematically, yes. But the bottleneck could be so far in the past that mutation has reintroduced genetic variation.

 

There were two migrations. The first was ~60KYA, during an ice age when there was a famine in Africa. They went all the way to Australia, where, due to the vagaries of the weather, there was a cornucopia of food sources. (Leaving just enough homesteads along the way that we find traces of their DNA on India's coastline.) The second was about ten thousand years later. That group found more hospitable conditions in western Asia and settled there, from which their descendants slowly colonized central and eastern Asia, then Europe, and finally the Americas. (It's not clear whether the speakers of the Afroasiatic languages were a third wave in the early Neolithic Era, or started in west Asia and migrated back to north Africa. After all these millennia of overlapping migrations their DNA is too mixed to analyze.)

But both groups were from the same tribe, the San or "Bushmen," who still exist. We all have their genetic markers.

 

The first appearance of human fossils gives us a fairly precise date of our arrival in a new location. By dating the fossils we know within a few hundred years when our ancestors first arrived in all the major regions: Australia, western Asia, eastern Asia, Europe, North America, South America, Polynesia/Oceania.

Actually we do. There are only two human gene pools outside Africa: the Native Australians and everybody else. Even though we are both descended from members of the same African population (the San or "Bushmen"), we can distinguish the genetic markers from two time samples of that population separated by ten thousand years.

Remember that 60KYA was the bottom of an ice age so sea level was at its lowest point, something like half a kilometer below its current level. The distances between the islands were much smaller than they are today and many of them were merged into single land masses. Navigating those waterways on stone age-technology rafts was not as daunting as it would be today. Besides, the Polynesians colonized all of Oceania and Polynesia--all the way to Hawaii and Easter Island!--rather recently in stone age-technology boats, so apparently it's just not as hard as it looks.

I'd guess that you're relying solely on carbon-dating of fossils. Using known rates of genetic drift provides another perspective on estimating the length of time during which a population has been separated from its origin.

Check out the astounding results of the research of Cavalli-Sforza, which is only a few years old, and outside the halls of science hasn't penetrated much further than the PBS audience. There are some good videos on YouTube of one of the PBS series, in which one of his acolytes traced the major migration routes of the early non-Africans. He even found traces of Australian DNA in people along the Indian coastline. Apparently they left behind a few colonies along the way, and they kept moving inland as sea level rose, and eventually intermarried with the later arrivals from Africa.

 

The topic of the thread is our species's current evolution. Since the majority of this evolution is now taking place at the higher level of the superorganism we call civilization, of which we are the component cells, his post seems as pertinent as anyone else's.

Considering the substantial impact of dogs on the evolution of civilization, it wouldn't even be off topic to bring them into the discussion.

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