It's a big claim. To estimate "1280 individuals" is... very precise.
The bigger issue, for me, is that I'm not sure how they can rule out the possibility that there were lots of other people around at that time whose lineages gradually died out. Modern genetic lineages may trace back to 1280 people (+/- the margin of error), but it seems pretty dubious to assume that those were the only people living at that time. It seems highly likely to me that there were infertile people, people who died young, people whose only living children were infertile or died young, etc.
(I did not read the original paper, so maybe they accounted for this, or maybe they that specify that this was a genetic bottle neck for modern humans, but not necessarily the actual size of the population.)
Then why say it's an issue?
It IS an issue with the article linked here, since it does not explain the research and causes readers to walk away believing there were only 1280 people.
What are the chances that every person alive today, for example, will still have living descendants in 400,000 years? If people 400,000 years in the future do a genetic study on themselves to determine how many of their ancestors were alive in the year 2023, what percentage of the 2023 population will they be able to account for? My guess is a fair bit lower than 100%.
"Hmm, this monkey looking thing isn't as tasty as a wooly mammoth, but it'll do."
(it's not like chimps don't catch and eat other primates)
It seems to me that if those lineages aren't in the DNA data, then they didn't --in the intervening years-- intermix with the lineages in the DNA data.
So, ipso facto, those lineages went extinct, and the 1280 ancestors posited in the study are the non-extinct lineages. QED.
Now, that doesn't necessarily mean they were isolated from each other, however. If we suppose that the population was actually 5000 people (just an example; I have no idea if this is a realistic number), then some percentage of those people died with having children, some may have seen their children die, etc. Of the 1280 people who still have living descendants, many of them would have had children with those people who did not, but those children (or grandchildren, etc.) eventually did not have any children themselves.
Within your own social circle, you likely know some people who will still have living descendant generations from now and some who will not.
Also, the way population dynamics work, lineages tend to die out quickly or not at all. Isolated populations can die out gradually, but it takes exceptional circumstances for a population to survive in the long term while remaining isolated.
It's be foolish of them to mask it intentionally.
Once independent estimates are made then you might synthesize an reasonable estimate.
Both the editor summary I'm science and the headline here don't place much emphasis on the precise number.
This is the actual paper, which (presumably, I cannot access) is specifically about how they made the estimate: Genomic inference of a severe human bottleneck during the Early to Middle Pleistocene transition:
Anyway, I surmised I would give away just about all my karma on the comment, but, hell, I just couldn't resist!
The fact that there is no comma (as in 1280,3333) is puzzling.