Homo Naledi: new homonid finds
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You mean a news page that always shows today's date instead of the date of the story?
Surely there's SOME way to date them.
What's the current science on "too old for radio carbon"? I read in this article ( http://www.smithsonianmag.com/history/showing-their-age-62874/?no-ist ) it's 60,000 years, but there are other methods, besides dating rock-age. Anyone know what they are?
National Geographic says it's about 50,000 years. But there are other techniques. When bones are buried in east Africa, there are datable layers of volcanic ash above and below to help out. When bones are in caves, dating is vastly more difficult. Methods are apparently too abstruse to describe in non-technical terms, or else the NatGeo writers hadn’t figured it out before deadline.
Greetings everyone. Just jumping in because I am a paleoanthropology nut, of the purely lay variety. Here is an excellent summary of the problems and hopes in dating these fossils: http://www.theatlantic.com/science/archive/2015/09/why-dont-we-know-the-age-of-t...
Basically, many dating methods including C-14 require destroying some material which they didn't want to do prior to fully categorizing the specimens. However, there is the 50,000 year limit with C14 and there is every reason to suspect these are FAR older than that. There is no breccia and practically no other sediments associated with these, which would commonly be available to help. There are other possibilities, which will be explored. They will attempt to extract DNA, but the humid conditions in S Africa make this much less likely. Electron spin resonance, flowstones, paleomagnetism are all possibilities. However there are other cases of fossil hominids from S Africa that have resisted all efforts at accurate dating. Hopefully that won't prove true here..
BTW: tonight PBS, NOVA: "Dawn of Humanity" about the project and the findings. Must watch TV!
More conversation about naledi here: http://www.librarything.com/topic/195595
If I remember correctly you and friends have read up on the
Big History approach to history...
Maybe you could start a thread on that. I am always left a bit vague around the edges on that particular approach.
And good luck on your cycling on Route 100; not easy to navigate in the best of times.
stellarexplorer, I'm astonished to think of viable DNA being recovered from fossils in excess of 50,000 years old. I've always assumed that Michael Crichton tales of dinosaur DNA were beyond implausible, though a fine premise for fiction.
Do you happen to know the age of the oldest hominin fossils to have had DNA successfully extracted from them?
A few points:
*From the 80's to the early 2000's - following the advent of PCR technology - there were reports of fantastically old ancient DNA finds, some into the tens and even hundreds of millions of years. No such reports have emerged in recent years, as the risks of contamination and the degradation of DNA have become better understood.
*A 2012 study in Nature reports a half life for DNA in ideal conditions of preservation of 521 years. http://www.nature.com/news/dna-has-a-521-year-half-life-1.11555
"The team predicts that even in a bone at an ideal preservation temperature of −5 ºC, effectively every bond would be destroyed after a maximum of 6.8 million years. The DNA would cease to be readable much earlier — perhaps after roughly 1.5 million years, when the remaining strands would be too short to give meaningful information."
So dinosaurs look like a bridge too far.
*The oldest generally accepted full genome is from a horse from about 700,000 years ago. Other old samples of DNA include mastodon (about 50,000 years old) and polar bear at 110,000 years old.
* The oldest hominid DNA is around 400,000 years old from the Sima de los Huesos cave in northern Spain. Those were the spectacular cache of bones that appear to be Homo heidelbergensis. And the DNA study was perhaps more spectacular, in that that it revealed a closer connection between those bones and those of Denisovans than Neandertals. Not something many would have been predicted prior.
It's streamable if there's not an upcoming rebroadcast in your area.
The results push back in time both the Denisova/Neandertal split and the earlier divergence of the ancestors of H sapiens even further, the authors suggest to as early as 550,000 to 765,000 years ago. It pays never to get too attached to dates and lineages in paleoanthropology ;)
All of this dances around another elephant in the room: the tenuous boundaries of these groups, distinctions of poorly understood significance formalized by the granting of species names, when in fact we are probably talking about a population model. We know it's not exactly right to discuss a Neandertal/H sapiens split, because we are part Neandertal. Populations diverged; populations interbred. And while we're at it, to what phenotypic and behavioral variations do the genetic differences and similarities among populations correspond? A subject for another day, another decade.
It will probably all make better sense when we have finally gotten over the myth of race.
Of course we'll also have to find a lot more fossils. One thing the NatGeo pieces made clear is that the tussle between East Africa and South Africa over the true location of the "Cradle of Mankind" is a sterile controversy, because we simply don’t have enough fossil evidence yet. Our whole present-day schema is probably going to go the way of Peking Man and Java Man.
For that matter, my school textbook made much of Cro-Magnon Man, a term since replaced by Anatomically Modern Homo Sapiens. I remember asking what the difference was between Cro-Magnon and Modern, and being told there really wasn’t one. Still our textbooks made a categorical distinction between the man in animal skins and the man in a business suit.
Of course the terms Caucasoid, Mongoloid, and Negroid appeared in that book. I think we implicitly understood that this list was in ascending alphabetical order and descending order of excellence. (Nobody draws racist conclusions on their own, just as they don't intuit the order of letters.)
There is indeed something resembling the issue of race at work here. And I agree that many things will make more sense when not distorted through the lens of prejudice. Hominin fossils are subject to judgment based on differences in appearance. Ancient hominins looked different than we do. That fact might well lead to bias in evaluating who and what they were.
But beyond that, we have other problems. More fossils does not always clarify matters; sometimes it confuses the issue. I'm all in favor of dig, baby, dig. In recent years, we have added Ardipithicus, sediba and now naledi to our list of past species, not to mention numerous proposed species of Australopithecus. Where do they fit? The concept of species is problematic when applied to extinct creatures. A biological definition of species - a group of potentially interbreeding populations reproductively isolated from other such populations, for example - is not useful when we cannot evaluate the capacity of populations to interbreed. A phylogenetic definition attempts to draw relations among groups based on morphological similarities and differences between them, but cannot assess whether there was continued gene flow between groups. Additionally, a lineage may change over long periods of time, such that it is impossible to determine at what point the degree of change represents a distinct species.
Without going on too long here, the NOVA episode addressed the need to revise the traditional linear picture of human ancestry, and Lee Berger presented an emerging metaphor to illustrate the history of Homo. A braided set of lineages, interbreeding and separating repeatedly, many genetic streams flowing downhill to the lake that is us, but impossible to clearly know how much any particular stream contributed to who we are.
I instinctively recoil from but have to acknowledge the possibility that we may never be able to say with certainty how the extant fossils should be conceptualized phylogenetically.