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Author | Topic: Neanderthals | |||||||||||||||||||||||
Quetzal Member (Idle past 5872 days) Posts: 3228 Joined: |
Although it does mean that some population geneticists sneer at us when we do population genetics. For some reason population geneticists spend a lot of time sneering at each other. No lie! And then they all get together over beers and sneer at everybody who ISN'T a population geneticist.
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PaulK Member Posts: 17822 Joined: Member Rating: 2.2 |
The studies on modern populations often use nuclear rather than mitochondrial DNA (early studies used proteins before we could analyse DNA directly). So any objection baed on the assumption that the data is derived from mitochondrial DNA must fail.
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Rei Member (Idle past 7013 days) Posts: 1546 From: Iowa City, IA Joined: |
quote: Personally, I don't see why we shouldn't treat the extinction of large mammals when humans were introduced in the same manner that we can look at the virtual extinction of most new-world races with the introduction of Europeans. It wasn't due to a single factor, but instead was due to *many* factors. Westerners brought disease, guns, and competition over resources, to name a few. No one factor brought them down. Likewise, it seems likely that the megafauna were doomed by the combination of disease, hunting technology, competition over resources (such as prey animals), artificially induced environmental alteration, and other corresponding factors - all at an ecologically delicate time (during a natural climatic change). One shouldn't get too comfy with the idea of natives as being "ecologically benign people", and that environmental destruction as being a relatively new concept. The desertification caused by the Anasazi, or the complete deforestation of Easter Island are striking examples of this. Westerners have only caused the extinction of one large mammal species in the New World (although a number of subspecies have been destroyed as well); the extinctions from the Native Americans (albeit, over a much longer period of time) astoundingly dwarf our record on this front. ------------------"Illuminant light, illuminate me."
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Mammuthus Member (Idle past 6475 days) Posts: 3085 From: Munich, Germany Joined: |
quote: However, to study it we have to be able to isolate factors where we can gather evidence. I for one have worked on (and still have some largely languishing side projects) on looking for pathogens in extinct megafaunal remains. The idea being to do a time series and see if some pathogens appear in megafauna at the same time as humans and their commensals arrive. Given that normal ancient DNA work on megafauna is a royal pain in the ass, you can probably imagine the world of hurt pathogen studies are from such lousy material. But it is still in principle something you can test. The same goes for climate change though there are problems with climate change as a singular cause. Overkill sounds nice but there is very little evidence for it. Sure it is probably a combination of factors. For example, mammoths presumably like other elephantids had a tremendous impact on their envirnoment. In Africa when elephants disappear from a region, the flora changes dramatically. This would open up the area to competition from other animals which could in turn cause the extinction of other species.
quote: One should not get too comfortable with the idea that the early migrants into Asia and across Beringia were able to slaughter everything in a short span of time either. Native Americans would not have to have been particularly peaceful or ecological minded. But it is telling that the end Pleistocene saw the extirpation of about 70% megafauna and then from 10kya on that ratio flipped even though there still were megafaunal species in abundance and the hunting tool kit progressed during that time. I doubt it was because the Native Americans suddenly decided overkill was a bad idea. Given the paltry evidence for overkill I just don't think it is a reasonable scenario as the mitigating factor even though I do think humans hunted megafauna...though I would like to know who would think it is a good idea to eat a mylodon? The have thick ossicles in their skin..probably lousy meat like modern sloths. Also the energy requirments for hunting a mammoth would outweigh the calories you get in return for killing it..though you could make a lot of wigs and impress the neighbors.
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Speel-yi Inactive Member |
You don't have to think Indians were ecologists, just that they would switch prey species when one type became scarce and another was more abundant. There were plenty of bison to hunt while the megafauna died out. There are a number of sites also with dead mammoths and no sign of human agency. Finding an actual kill site is a really big deal and hard to come by.
There were also some other fauna that became extinct and did not have any value as a food source like the short faced skunk, Brachyprotoma obtusata somehow I can't see those things being hunted in preference to things like deer. ------------------Bringer of fire, trickster, teacher.
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sfs Member (Idle past 2533 days) Posts: 464 From: Cambridge, MA USA Joined: |
quote:The reason there's a problem is that the effective population size is the size of the entire population, not the size of regional subpopulations. The entire human population has an effective size of about 10-20 thousand; the entire non-African population has an effective population size of well below 10,000. The small size is reasonable for a group or collection of groups moving out of Africa and then expanding, but it is not reasonable for a population spread across many thousands of miles and split into many smaller subpopulations. I could understand an archaic population in China of a few thousand, but I can't understand a population of a few hundred in China, a few hundred in southeast Asia, a few hundred in Iberia, and so on. MRH requires that every one of the populations was very small, and at the same time that there was a high enough density across the entire range to maintain substantial gene flow. That just doesn't seem possible. This is not based on mtDNA, by the way. Y, X and autosomal diversities are all consistently low, and autosomal linkage disequilibrium is very high outside Africa. Similarly, X and autosomal loci, as well as the Y and mtDNA, tend to have their deepest branches in Africa, not elsewhere.
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sfs Member (Idle past 2533 days) Posts: 464 From: Cambridge, MA USA Joined: |
quote:My theory about this phenomenon is based on my background in physics. Like population geneticists, theoretical physicists work in a solitary, abstruse field with lots of nifty equations. Unlike pop gens, however, theoretical physicists get a lot of respect from their experimentalist colleagues. Population geneticists don't get a lot of respect, or even awareness of their existence, from other geneticists, and that makes them cranky. (I didn't say it was a good theory.)
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Quetzal Member (Idle past 5872 days) Posts: 3228 Joined: |
It's probably a good theory. However, it's not our fault. They're the ones who keep coming up with equations it takes a mainframe to make any sense of. After all, we probably wouldn't be in one of the field biology disciplines in the first place if we could handle math more complex than one, two, three, many, lots. I mean, we could all go get real jobs where we weren't forced to hang around on tropical beaches playing frizbee waiting for turtles to come ashore so we can daub florescent paint on their plastrons...
[edited to add: Sorry moose. I'll be good...] [This message has been edited by Quetzal, 10-14-2003]
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Speel-yi Inactive Member |
quote: It would mean having an effective breeding population of around 10,000 spread over two continents. This would not be that big of a stretch at all. First we would have high inbreeding and this would not be surprising since most small scale societies still participate in marriages between cousins by preference. University of Manitoba - University of Manitoba - Contact Information
quote: Humans have not been panmictic for a long time and it's only been recently that the incest taboo has been applied to cousins. I would expect inbreeding to be very much part of the genetic background for ancient humans. In small scale societies, the genetic relatedness of full sibs should be somewhat greater than the 0.5 we would see in a large, random mating population. The incest taboo would still come into play as humans seem to prefer mates that they were not reared with, young people would go to great lengths to find an exogamous mate. (A long trek for some good sex is not too hard to imagine now is it?) We see an example of the incest taboo being naturally applied between non-related individuals that were reared together in the modern Kibbutz. http://www.ed.ac.uk/ces/tiy/tiy98papers/DAR_Y.html
quote: There seems to be an inhibition to mating between individuals of cohorts reared together and the preference is for mating outside of a community. Traveling for a mate is not too much of a stretch.(Evolutionary psychologists cite the Kibbutz as an example of an inborn incest taboo.) So we would see populations from demes with effective breeding populations of around 500 and then periodic mating between demes from adventurous youths traveling fairly great distances to find a suitable mate. One other thing is that in modern Africa we see at least 3 distinct racial types, while outside Africa we see the bulk of the populations are made up of only 2 racial types. ------------------Bringer of fire, trickster, teacher. [This message has been edited by Speel-yi, 10-14-2003]
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Rei Member (Idle past 7013 days) Posts: 1546 From: Iowa City, IA Joined: |
If you'll recall, I wasn't arguing for the "hunting-only" theory - I was arguing that a combination of factors is likely the key. I do, however, believe that hunting was *one* of them, but that hunting alone would never have caused such widespread extinctions.
I do, however, think that you underestimate the value to a society of a megafauna kill. I don't have figures for mammoths, but after watching a show about the Donner party and cannibalism, they mention that the average adult male human has about 4.5 lbs of protein, enough for 60 people for one day. Assuming a 180lb human and a 8 ton mammoth, with simply scaling these figures up by body mass, we're looking at about 400 lbs of protein, feeding a whopping 5,400 people for a day (or more realistically, a smaller number for notably longer). Do you have more precise figures (also addressing things like calorie consumption)? Also, where did you get that sloth meat is bad? It's eaten in some parts of South America. I would argue that the reason some of North America's large mammals survived is that a steady state was reached before extinction. Early humans were no more migratory than many other predators, especially without horses. If left in a fairly stable environment for long enough, most species tend toward equilibrium. Not only do the buffalo, for example, adapt, but also do the social values of the native tribes. They are selected apon - through natural selection - based on their ability to not kill off all of the food supply in the area. ------------------"Illuminant light, illuminate me."
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Speel-yi Inactive Member |
quote: This is only for K-selected species, r-selected species will go through boom and bust cycles and some of these appear to have gone extinct as well. It's really tough to overhunt r-selected species and they seem to do better when they are prevented from the boom and bust cycles. A single mammoth would feed a few people for a long time, so you kill one or two a year per group at maximum. They probably would have greater mortality from non-hunting causes anyway. Plus, who's to say that Paleoindians didn't just wait for a non-reproductive adult mammoth to leave the herd because they couldn't keep up and then make a kill on a solitary adult that wasn't in its prime? All the Indians would have done would be to speed up the inevitable. ------------------Bringer of fire, trickster, teacher. [This message has been edited by Speel-yi, 10-14-2003]
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Rei Member (Idle past 7013 days) Posts: 1546 From: Iowa City, IA Joined: |
R-selected species tend to be short lived, have high mortality, numerous offspring, rapid reproduction, a small build, and are often pioneer species. How do you conclude that most megafauna were R-selected?
------------------"Illuminant light, illuminate me."
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Speel-yi Inactive Member |
Megafauna are K-selected. But a lot of extinctions are r-selected species.
There is a hypothesis out that presents the idea that humans preyed upon all age groups of species and extreme k-selected species were outcompeted by lesser k-selected species such as bison. This is due to the unusual human practice of hunting not just the old and young from a population as they tend to hunt reproducing adults as the opportunity presents itself. Then here's another one to look at:
Heat ovulation reduction hypothesis
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Rei Member (Idle past 7013 days) Posts: 1546 From: Iowa City, IA Joined: |
quote: I was discussing the extinctions of the megafauna. ------------------"Illuminant light, illuminate me."
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Speel-yi Inactive Member |
Yup, knew that. But part of the problem with the over kill hypothesis is that there is a simultaneous extinction of non-megafaunal species. Another is the fact that one big animal will feed a few people for a long time, especially if you can freeze the meat. Another is that African megafauna have survived fairly well despite human predation for thousands of years.
I really have a tough time with the pathogen hypothesis as well. We see very diverse species all disappearing at the same time. What it's going to take is a species by species evaluation of what happened and then we have to consider what effect each species has on the ecosystem as a whole. Maybe some grasses did much better with mammoths stomping on them and they too died out when the mammoths did as well. Then in turn you have rodents that have lost their preferred food and they don't do so well. ------------------Bringer of fire, trickster, teacher.
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