This is worth a quick note, both for the new methodology and the mildly interesting results. A new article in Proc. Nat. Acad. Sci. USA reports the use of sedimentary ancient DNA (“sedDNA”) analysis to show that both the wooly mammoth and the horse survived in North America several thousand years later than previously thought. (Horses, which evolved largely in North America, went extinct around time that humans arrived here from Asia, and were later re-introduced in domesticated form by colonizing Europeans.)
Using fossils to determine when a species went extinct always yields a date older than the target date, for it’s unlikely that the latest fossil is from the last remaining population (this phenomenon is known in paleobiology as the Signor-Lipps Effect).
To get a better handle on extinction of the North American megafauna, Haile et al. simply extracted DNA from the permafrost at a site on the Yukon River floodplain in central Alaska, and, by sequencing, assigned it to various animals groups that became extinct. By correlating the DNA sequences with the date of the permafrost layer from which they were taken, the authors could determine the most recent time the carriers of that DNA lived. (Sediment dating was done by the measurement of optically stimulated luminescence [OSL], a recently devised way of using the luminescence of minerals to determine when they were last exposed to sunlight.)
Halle et al. found this: both horses and mammoths persisted in Alaska up to a time between 10,500-7,600 years b.p.
This is several thousand years later than the previous “extinction dates” based on fossils themselves, about 13,000 and 14,000 years b.p. for mammoths and horses, respectively.
What does this mean? Well, the earlier coincidence between fossil-based extinction of these large beasts with the arrival of humans in North America (about 14,000 years b.p.) had led to the conclusion that humans quickly hunted these beasts to death, or that they went extinct due to rapid climatic changes during the late Pleistocene. It could still be true that the extinction of these beasts was promoted by humans, or by climate, but that this didn’t take place so quickly after human contact. As the authors say,
. . .the sedaDNA evidence for mammoth and horse persisting into the Holocene in interior Alaska is incompatible with such rapid extinction and indicates that late-surviving mammoths in the New World were not confined to islands in the Bering Sea that might have afforded protection from human hunters (10, 34). The protracted survival of mammoth and horse is also inconsistent with the hyperdisease hypothesis (5) (which requires their swift demise following human contact) and with megafaunal extinction due to end-Pleistocene environmental changes associated with abrupt climatic events (35), altered vegetation patterns (2), or intense wildfires sparked by a presumed extraterrestrial impact (6, 7).
Here’s a nice graphic from the paper:
Fig. 1. (caption taken from the paper): Stratigraphic profile and location (see inset map) of the Stevens Village site. Elevation is height in meters above river level, and age ranges (in calendar years) are shown at the 95 and 68% confidence intervals for radiocarbon (14C) and OSL, respectively. OSL ages were obtained from quartz sediments and 14C ages from plant macrofossils. Inset photo shows detail of buried vegetation (with arrow at shrub root) and lateral continuity of paleosol at 5 m elevation. The mammalian taxa identified from sedaDNA sequences are shown by symbols, with the scientific names given in Table 1.
I’m not a paleobiologist, nor an expert in dating, but the authors did deal with several possible problems, for example the objection that older DNA could simply have been washed into younger sediments.
______________
Haile, J. et al. 2009. Ancient DNA reveals late survival of mammoth and horse in interior Alaska. Proc. Nat. Acad. Sci. USA. 106:22352-22357.
One thing I’ve wondered about is if it is possible that mammoth hair could be set on fire. If so, a fire-wielding animal like humans would likely have an easier time hunting them than is often supposed, especially considering how much hair mammoths had.
Just a question/suggestion.
Glen Davidson
http://tinyurl.com/mxaa3p
That’s a very good idea you have there. My related theory is that primitive humans may also have used this method to treat infestations of crab lice.
Continuing on your line of thought, Barry, early women must have used fire to singe off their leg and armpit hair due to a relatively recent rise in frequency of the adaptive hairless-attraction gene. Nowadays, of course, women use more practical grooming tools to attract mates, but this example of adaptation is obvious and proves evolution.
Ouch!
Let us know how the testing of your hypothesis works out.
This is definitely a different meaning of getting down and dirty in the mud.
I’m stunned that one can do analysis of animal extinctions just by sequencing DNA in mud. That is so damned awesome.
This science stuff is pretty awesome. Makes me lament on some days that I work with computers (though – I work with really cool and powerful computers, so that makes it better most of the time 🙂 ).
If I had a chance to do it all over again, Physics or Biology would win out over IT easy.
I wonder if something similar could be done in Australia, since the evidence seems to suggest a massive extinction of megafauna not long after humans arrived.
DNA in *sediment* plus the indicated time frame is consistent with mammoths becoming extinct due to a global flood.
Same evidence, different world view!
Blinders are useful on racing horses, not so much when trying to understand the history of life. All the geological evidence shows the christian flood is a typical christian lie. The biological evidence shows the christian god idea is either stupid, an ass, or a typical christian lie.
so notagod you don’t believe the melting of the great ice sheets didn;t cause a global flood? I think people who believe that melting ice sheets can cause global floods are not the stupid ones.
Not really if you consider the date of creation 4004 B.C., that’s 6014 b.p. Your “hypothesis” doesn’t fit the evidence.
Ummmm…. (consults manual of creationist arguments…). The sediments are dated older than they really are because decay of radioisotopes was more rapid during the initial stages of the flood.
Not an expert on”dating”? Oh, that’s too bad…
Now in earnest, the hypothesis that these creatures went extinct as a result of human action goes along with the “Clovis First” model of settling of the Americas which maintains that the Americas were first settled after the last ice age. The competing model is that they arrived much earlier. While I am by no means an expert in the field it seems to me the new evidence may favor the pre-Clovis model.
> DNA in *sediment* plus the indicated time frame is consistent with mammoths becoming extinct due to a global flood.
Where’s the evidence of the flood? Or is that part of the magic, as well?
The sediment itself was deposited by the floo….bzzzzzzzzzzzzzzt.
Whoa, ‘scuse me, I think my body and mind were taken over by Ken Ham for a bit there. No worries, your irony meter is working just fine…
How do you know a fragment of DNA is from mitochondria?. And once you know it’s mDNA, hoe do you know it’s from a mammoth or horse. Also #4 above, permafrost in Australia?
I am not sure about this, but I think that mitochondria have DNA sequences that are only found in mitochondria.
So horses and mammoths survived in North America up to historical times. Not very advanced historical times, but historical times.
Now since some Central Eurasian tribes were riding horses about then (or so I’ve heard), how could we encourage such a tribe to migrate east, in time across the Bering Strait into North America with their horses. At the very least with the knowledge and tradition of horse riding, adapting their skills to North American horses. How would the world change if horse nomads had invaded the Great Plains around 2,000bc?