Re: News: Study says near extinction threatened people.
- From: Ron O <rokimoto@xxxxxxx>
- Date: Thu, 24 Apr 2008 17:18:41 -0700 (PDT)
On Apr 24, 12:23 pm, Martin Andersen <d...@xxxxxxx> wrote:
Ye Old One wrote:
The report notes that a separate study by researchers at Stanford
University estimated the number of early humans may have shrunk as low
as 2,000 before numbers began to expand again in the early Stone Age.
I wonder, I really do, how they can they tell that there weren't many
other early humans, coexisting at the same time, but who happen to not
have any living descendants today?
Humanity could hardly be considered at the verge of extinction if there
was eg. hundreds of thousands of other humans that, for whatever reason,
did not interbreed with any of those 2,000 (or the descendants of either
category with each other).
Lets say early humans lived in 10 hypothetical isolated communities or
roaming bands (numbered 0 to 9) and the "graph" below has the population
size normalized to a fixed "width" over time:
+---Population-->
| 0123456789
| 0122456889
| 1122556889
T 1112568889 <----- *
i 1155566888
m 1555568888
e 5555588888 <----- **
| 5555555588
| 5555555555 <----- ***
V
*) Let's assume a total population of 20,000 here. Meaning every letter
roughly represents 2,000 early humans.
**) Assuming a global population of 10,000 here, each letter represents
1,000 early humans.
***) No longer any reproductively isolated communities (all 5's).
So at time ** there were half as many people than at time * making it
more of a population bottleneck, but there was 5,000 ancestors, of
people around in the end, compared to only 2,000 at the twice as
populated time *. Meaning genetic analysis would point at the wrong
time. Or am I mistaken? (I would expect to be)
Another example: Say someone passed a law preventing people of some
country with a tiny population, from breeding with the rest of us. Now,
over the next ten thousand years, the tiny population happened to
replace the rest while keeping the combined population at some fixed
number until finally only one group existed. Would future geneticists
using that method, think the species was at the verge of extinction at
the time the law was passed?
They can't discount it. One reason is that we have data indicating
that Neandertals were around as late as 30,000 years ago so they too
survived this bottle neck, but their mitochondrial genome sequences
are not found in modern human populations. There may not have been
extensive interbreeding between Neandertals (Homo sapiens
neanderthalis) and Homo sapiens sapiens. Some anthropologists have
claimed for a long time that Neandertals were a separate species (Homo
neanderthalis). We may have also coexisted for a time with other
archaic Homo sapiens. All the study can conclude is that we didn't
extensively interbreed with other Homo populations existing at the
same time.
Ron Okimoto
.
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