Re: [asa] Two questions... (biological bottlenecking with Adam and Eve)

> Again I ask, because I don't see a clear answer (the problem may be on the sender or receiver side), how can anyone trace something back to "the first human?" <

The fundamental problem is defining the "first human." If your
definition includes some feature that is amenable to genetic analysis,
then genetics might help you track this down. If your definition
includes some feature traceable in the archaeological record, then
archaeology might help in pinning it down.

From a Biblical perspective, I think that the essential aspect of
"first human" is spiritual. If, and if so, what sort of, physical
trace this would have is not especially clear to me.

Taxonomically, one could call the first Homo sapiens sapiens, or the
first Homo sapiens s.l., or the first Homo sp. the first human, in
which case there would be particular physical features to look for.
However, there's no evident a priori reason to pin down first
spiritual human as corresponding specifically with one of those. Some
people do try to make such a correlation, but it must be speculative.

>For example, if someone says everyone today can be traced back to a mitochondrial eve, tell me how mitochondrial eve's mom is different, in that someone could say mitochondrial eve is the first human female but her mom isn't? I really don't get it, but I want to. (And I'm talking only biologically- not spiritually- this is a purely scientific question related to the human genome.) <

Perhaps an illustration from amore recent incident will help. A few
years back, there was a big news item about a genetic study "proving"
that Thomas Jefferson had fathered a son with a slave. What the study
demonstrated was that one of Sally Hemming's sons was paternally
closely related to Thomas Jefferson. What it did not prove was
paternity. In particular, there was no discussion that I saw about
the possibility that the Jefferson genes were already in the slave
community. Thomas or a relative of his on the father's side could
have been the grandfather rather than the father, for example. We
also do not have direct evidence about Thomas Jefferson's Y
chromosome. No direct legitimate male descendant of TJ is around for
study, so we have to rely on slightly more distant relatives for
comparision with the descendants of the slaves. If there was anything
unique in his Y chromosome, we can't prove it (short of digging
someone up and hoping that the DNA is in decent shape).

The claims about mitochondiral Eve and Y chromosome Adam do not claim
that the immediate parent was an ape. For one thing, the guesstimated
dates are well within the time when you have fairly advanced Homo.
More importantly, nothing is remarkably different about the "Eve" and
"Adam" in this context from their parents-they just happen to be the
spot where the genealogies converge.

Suppose I meet someone who says "We must be related-my grandmother was
a Campbell." We start looking into genealogical records and determine
that we share a great great great grandfather. There's nothing
remarkably different about the great great great grandfather versus
his father. There were many other Campbells around at the time. It's
just that, for the group of interest (i.e., my new acquaintance and
myself), our ancestry converges at the point of the great great great
grandfather.

In sexually reproducing organisms, usually the DNA from each parent
gets mixed during meiosis (when the gametes are produced.) Thus, on
average each person has one quarter of his or her genes deriving from
each grandparent, but the exact selection is somewhat random, and
within one gene you can have part from one and part from another. As
a result, much of the genome gets a lot of mixing and is hard to trace
precisely. However, certain bits of DNA transmit more directly from
parent to child and undergo little if any crossing over. These
include mitochondrial DNA (in the mitochondria in the cell,
transmitted in the cytoplasm of the egg cell) and Y chromosome DNA
(normal males have one copy and females no copy, in mammals, so
there's no matching chromosome for it to swap with). Because it
doesn't get mixed around, changes accumulate mostly just via mutation.

The question for mitochondrial Eve is "Suppose I take all living
people. Who's the most recent common female ancestor of all of them?"
 At any given time in the past, there would be a certain number of
versions of the mitochondrial genome. If a particular woman has no
female descendants in a particular generation, then her mitochondrial
lineage will be lost from the population. Going far enough in time,
in a finitite population, eventually all but one lineage will
disappear. Mutations are creating new versions, but they ancestrally
derive from older versions.

IF having a spiritual human nature is tied to physical descent, then
presumably the last common ancestors of all modern humans would also
be fully human. However, this does not rule out the possibility that
the first true humans were ancestors of the mitochondrial Eve and Y
chromosome Adam. In fact, if you do start out with a single pair,
then the chances of losing all but a single lineage a few generations
later (not to mention at any subsequent point when the total
population is small) will still be quite high.

Envisioning the process in the fututre might help. You may have
encountered the science fiction scenario with the premise that due to
some catastrophe, only a handful of humans can be saved out of the
total population. Whoever is saved determines the genetic makeup of
future humanity.

> To me it seems like someone is proposing that an apelike creature gave birth to a human, and I don't understand that- given the ring species phenomenon.<

There's a gradual sequence of decreasingly apelike and increasingly
humanlike in the fossil record. If you identify one feature as being
the key to humanity, you can have a "human" with "ape" parents, but
you might have trouble convincing other people that the particualar
feature you select really is a good choice. In a somewhat less
contentious context, having a jaw joint like modern mammals has been
the traditional feature to draw the line between mammal-like reptile
and true mammal. In fact, at least one species is known with a
double-jointed jaw, so it doesn't solve all cases (plus not everyone
likes the choice of a particular feature as the dividing line.)

> Here's a modern example of ring species, since you said you weren't aware of modern living examples (with the seagull):
> http://en.wikipedia.org/wiki/Ring_species

I'm familiar with plenty of modern ring species-what I meant was that
there was not a suitable case within humans.

> Exactly my point. When someone claims there is a mitochondrial eve, they are saying that it is the first human- how is that defined such that mitochondrial eve's mom is not human? Obviously, mitochondrial eve is related to her mom!<

Mitochondrial Eve or Y chromosome Adam is a bit of a misnomer.
They're just saying that the individual in question is the most recent
common ancestor of all present-day mitochondrial or Y chromosome
lineages, not that they were any different from their parents or
contemporaries in any obvious way.

> I have a hard time accepting your hypothetical analogy with Noah, because we both know it isn't true- there was no worldwide flood in our opinion. It is like using the old analogy of a frog in a pot that is brought to boil- bad illustration because it isn't true. I don't see how a goofy story can be used to illustrate something scientifically. It could be like if I believe that people could fly if they knew the secret- giving an analogy of santa's flying reindeer to illustrate the point.<

Mainly it was selected because it gives a familiar, small set of
ancestors. Although it is possible to devise a scenario in which all
modern humans descend from Noah after a regional flood takes out the
rest of the human population, it does require a number of difficult
assumptions (again, you have to push him rather far back in time,
assume huge gaps in the genealogies, etc., just as you would for Adam
and Eve being physical ancestors of all later humans).

> Maybe the big mistake here is in thinking that mitochondrial eve is the first human- which science says is not the case. Rather than defending how one person can be the parent of all humanity, maybe the thing you should be doing is explaining how, instead, evolution happens in populations and not through a single founder?<

Although I think it is unlikely that every modern human is physically
descended from Adam and Eve, the possibility cannot be eliminated,
especially without a universally agreed upon decision as to where to
draw the line between truly human and not quite.

The issue of evolution in populations rather than a single founder
ties into very contitious issues (within evolutionary biology) about
group selection, etc. On the one hand, populations change over time,
and there are certain factors (especially in organisms such as apes
and humans where information can be exchanged through communication,
not just through genes) that affect success of a group. On the other
hand, each individual's genome has to function well enough to survive
and reproduce, no matter what the population as a whole does.
Especially in a small population, mutations can spread and take over
quickly. If they convey any selective advantage, they will be
especially likely to spread; if they are harmful, then they are less
likely to spread, with all sorts of additional caveats about the
genetic details underlying any one character.

>If Dr. Campbell can come to say that a single biological male/female (literal Adam/Eve) is impossible<

It's not absolutely impossible. It totally depends on how you define
the line between human and non-human. If you think that all those who
are fully human must be physically descended from Adam and Eve, and
you accept the evidence of genetics, paleontology, etc., then you will
have to place them fairly far back in time and accept the possibility
that the fruit was a banana rather than an apple, but it can be done.
I don't think that such a scenario is necessary, but I am being very
strict in my usage of "impossible".

Under a scenario in which Adam and Eve are selected out of an existing
population and choose to rebel, whereup a fallen spiritual nature is
assigned to the full population, it would not necessarily involve
clothed, spiritual and unclothed, non-spiritual groups co-existing.
One version would have everybody infused with the same fallen
spirituality at the same moment. Another would have a similar process
taking place multiple times in multiple groups. However, the specific
example of clothing is not necessarily precisely correct.

If you assume that wearing of clothes is a post-Fall phenomenon, then
you have to push the Fall back in time. The oldest evidence of
clothing (which tends to decay and not get preserved) is Homo erectus'
ability to spread into northern climates. Some sort of cover would be
needed. Besides, if they normally didn't wear clothes, he wouldn't be
Peking man-he'd just be staring. However, if you assume that hominids
had rather advacned mental capabilities before they became spiritually
human, it is possible that they were using some form of clothing
purely pragmatically, and that the post-Fall innovation was the need
for modesty.

-- 
Dr. David Campbell
425 Scientific Collections
University of Alabama
"I think of my happy condition, surrounded by acres of clams"
To unsubscribe, send a message to majordomo@calvin.edu with
"unsubscribe asa" (no quotes) as the body of the message.