Re: Date for Last Common Ancestor?

T&B Schmal (
Sun, 11 Aug 1996 23:27:00 +0000

I wrote:

I am interested in bracketing the dates for the last common ancestor of
humankind. Would a good guess be somewhere between "Eve" and the
appearance of modern man - say, between 200 and 50 Kya? It seems to me
that dates outside this range would be impossible.

Tom Schmal

> To establish the existence of a "Last Common Ancestor"by
> logical means only will require quite a lot more than you have supplied,
> starting with a clear definition of what is the "Last Common Ancestor" for
> a species.

What I ment by LCA is tough to define in genetic terms, but from a lineage
point of view, it is a person (well, really a pair of persons) from which
all of us living are directly descended, ie, each of us can trace our
ancestory to that one person. Now, we can also all trace our ancestory to
that person's mother but she would not be the last common ancestor, she
would be the second-to-last.

As an analogy - at the Schmal family reunion, all the great grandchildren
can trace their lineage to great grandma Schmal. They can also trace
their lineages to many other great grandmas (through my wife's parents,
for example). But for all the children at the reunion, great grandma
Schmal is the LCA.

Eve, like the missing link, the first primate, the first single-celled
organism, is one of our common ancestors. At this point she is the last
Known common ancestor. As more genetic analysis is done she will
(probably) be displaced by someone more recent. My question is what is
the most recent possible date that will be eventually determined to be the
date of the LCA.

I hope that does not muddy the waters too much.

Tom Schmal