Thread: does DNA prove humans have been here for at least one hundred thousand years?

I wish I understood it beter. It's a fascinating subject. Filix.

No, DNA itself does not prove this.

DNA shows variations between certain proteins humans use, intronic DNA differs much more because it's not as evolutionary pressing as exons.

DNA does show we come from apes, and apes from smaller mammals, like mongoose, or chipmunk, and them from mice like creatures. The time passed by from generation to generation can not be predicted this way. That's what carbon dating, ice dating, residue or cesium dating is for.

The furthest you can go with time, is knowing minimal generation time, then looking at the number of mutations per generation, and then looking at the first human, to the two most different humans (still healthy). Then, if we origin from 1 couple, we could predict how long ago it could be. Give or take 50%.... Which is a huge uncertainty..

once molecular clocks have been calibrated they can be pretty useful in estimating past splits of related lineages

The molecular clocks are not accurate as you would like to believe. They are finding now with doing more species genetics that many species share identical sequences with no relation to each other. The tree that science stands by in descent with modification in each of the branches is not as clear as they once thought it was.

Originally Posted by Zwolver

Give or take 50%.... Which is a huge uncertainty..

I think molecular clocks are more accurate than this. If you use a gene which has very slow genetic drift, like 18S rDNA then it will be even more accurate. Nick Lane used a nice analogy: if you walk into a clock shop and some clocks are ticking slower than others and some clocks faster, but the majority of the clocks are all in and around the same time, say 3:30, you'd assume the time is 3:30. In other words, as more and more gene sequences become available, and more comparisons can be drawn, we can say how old certain evolutionary events occurred with greater confidence.

Originally Posted by HFS

Originally Posted by Zwolver

Give or take 50%.... Which is a huge uncertainty..

I think molecular clocks are more accurate than this. If you use a gene which has very slow genetic drift, like 18S rDNA then it will be even more accurate. Nick Lane used a nice analogy: if you walk into a clock shop and some clocks are ticking slower than others and some clocks faster, but the majority of the clocks are all in and around the same time, say 3:30, you'd assume the time is 3:30. In other words, as more and more gene sequences become available, and more comparisons can be drawn, we can say how old certain evolutionary events occurred with greater confidence.

The speed of evolution or change, is not set. It's variable to limiting factors, and expansions of the species. Taken everything in account, predicting is more accurate yes, but still not unfallible.

Yes but nothing in science is infallible. It would be unscientific to assume otherwise.

A scientist on youtube says that human DNA mutates at a pretty reliable rate and they can trace these mutations back. Like following the branches of a tree back to the trunk. Its not a greatly acurate method, but it does give a rough Idea when humans migrated, and a very deffinate Idea of where. It doesen't lead back to Mt Arrarat 4000 years ago, but to africa about 50,000 years ago, just as other dating methods sugjest it should. This was by AKA potholer on youtube. Would you agree with this? Filix.

Bones found in a cave in South Africa were almost certainly Homo sapiens, and have been dated to 200,000 years ago (plus or minus a bit). This is more reliable than DNA dating, but the DNA supports the view that our species is a good 200,000 years old.

Originally Posted by skeptic

Bones found in a cave in South Africa were almost certainly Homo sapiens, and have been dated to 200,000 years ago (plus or minus a bit). This is more reliable than DNA dating, but the DNA supports the view that our species is a good 200,000 years old.

I still don't understand the line between one species and the other. I mean, what defines homo sapiens sapiens as a species. Our dna keeps changing, and at some point we will be multiple species. Though for now, we are pretty stable, surprising as other species have formed multiple different kinds in the same time period. Look at madagascar, in 600.000 years 5 different branches have sprouted, and there are now over 150 different small primate species.

Zwolver

That is a very good question.
The 200,000 year old human bones were not identical to modern human, and might have been a different sub-species. However, the 'experts' involved classed them as Homo sapiens. Since no one is able to carry out interbreeding experiments with that population, the definition as the same species is based on criteria that are partly subjective. Sufficiently similar = same species. An arguable position, but probably as sound as we can get.

from what i've read, it seems that our sub species went through a genetic bottleneck about 70kybp when tobo blew during an already cold period of glaciation---which may have droped global means down another 6 degrees for hundreds of years

assuming that diverse pockets survived(inside and outside of africa--india, southeast asia?), and later reunited and shared genes-----then some of our lineage may date to that reunification, while some other "modern" dna may be hundreds of thousands of years older
(if we're 4% neanderthal and x%denisovian and? does our "modern human"dna line start when the genes became shared?)
...
we have a very small sampling-----showing few identifiable transition groups and dna evidence for only a few thousands of years
with any luck at all
we may find a 90,000 year old corpse poking out of a northern glacier with viable dna
.............
our dna is like the bride's wedding poem---"something old, something new, something borrowed, ..."
one day, we may know where to set the markers for our ancestral subspecies, and ...where to set our own
...........all is a guess?