RE: [asa] Out of Africa? (DNA studies to find the first humans)

David Opderbeck said:
"It is more accurate to state that the history of the human genome can
be traced to Africa through genetic studies. "

But how do they know when they've hit a genetic "stopping point" as they
study regression? Don't they need to have a "stopping point" in their
regression studies to declare that they've found out where "humans" came
from? What genetic marker or sign are they looking for?

...Bernie

________________________________

From: David Opderbeck [mailto:dopderbeck@gmail.com]
Sent: Thursday, June 19, 2008 1:58 PM
To: Dehler, Bernie
Cc: asa@calvin.edu
Subject: Re: [asa] Out of Africa? (DNA studies to find the first humans)

Bernie asks: How can DNA studies find a "first human" if we don't even
know what that looks like?

I respond: My understanding, and others more expert can correct me if
I'm wrong: they can't. DNA studies can trace the genealogies of genes.
It is more accurate to state that the history of the human genome can be
traced to Africa through genetic studies. What constitutes "human" in
terms of physical anthropology depends on various, often disputed,
physical characteristics. Some very ancient extinct species that
physical anthropologists consider "human" would probably looked and
acted much like contemporary apes, though some ancient extinct species,
like Homo Rhodensiensis, which dates to probably 650 kya, possibly
looked much like us.

A really fascinating book the illustrates this vividly is "The Last
Human: A Guide to Twenty-Two Species of Extinct Humans." It's an
expensive book, but it includes stunning color recreations of extinct
human species based on forensic techniques that apply muscle structure
to the fossil bones. (Just a warning -- only pick this up if your
applecart about finding an easy place for "Adam" has already been upset!
You can't stare into the eyes of Homo Rhodensiensis and conclude that it
was just an ape -- at least I can't!)

Whether "human" is properly reducible to physical anthropology is hotly
debated, particularly by those of us who assert a spiritual component to
human nature. Even many "secular" physical anthropologists see
something very different happening in human culture and capacities about
40 kya (see Ian Tattersall, "The Fossil Trail: How We Know What We
Think We Know About Human Evolution" -- again, not for those who aren't
ready to confront some tricky issues).

Wentzel Van Huyssteen's Gifford Lectures, "Alone in the World: Human
Uniqueness in Science and Theology" discusses this from a Christian
theological perspective (though not an "evangelical" perspective).

On Thu, Jun 19, 2008 at 4:27 PM, Dehler, Bernie
<bernie.dehler@intel.com> wrote:

        Hi all- a question for something I don't understand. I hear of
DNA studies to determine where humans originated (out of Africa, etc.).
But how could that be determined since we don't even know what a 'human'
is? Seems like the quest assumes there is some sort of DNA line where
you have a non-human, then a human. Seems to me like evolution says
change is gradual- no dividing line.

        For example, apes have one more pair of chromosomes than human.
Two ape chromosomes fused to make 1 human chromosome (human chromosome
number 2, I believe). Therefore, at some point an animal existed that
had these chromosomes fused. Is that a human at that point? What does
it take to be human? How can DNA studies find a "first human" if we
don't even know what that looks like?

        A short answer would be fine. I won't be able to read any
references to books- already have a backlog of books to read.

-- 
David W. Opderbeck
Associate Professor of Law
Seton Hall University Law School
Gibbons Institute of Law, Science & Technology 
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