Brent Foster asks:
>Is it possible to show
>by DNA studies that it is genetically impossible for humanity to
>have descended from two individuals, say Adam and Eve?
Yes IF you require a certain time frame for Adam and Eve. The amount of
genetic variability in human populations can not have arisen by mutational
processes, at the rate we observe mutational processes occuring, if they
lived within the past 2 million years. There has not been a bottleneck down
to 2 people over that period of time and this is demonstrable with the age
of some of the genes we see in nuclear genetics. I have a web page which
talks about this issue and the age of certain genetic systems. See
http://www.glenn.morton.btinternet.co.uk/hegene.htm
There has been an ongoing debate about the MHC genes which are involved in
our immune response. Ayala et al write:
"It has been claimed, in particular, that a severe population
bottleneck of only one pair or very few individuals preceded the
evolution of modern humans. This claim has been erroneously
sounded on the inference that the mitochondrial DNA polymorphisms
of modern humans can be traced to a single woman who lived some
200,000 years ago. As we shall show, DNA polymorphisms in the
major histocompatibility complex (MHC) of humans and other
primates manifest that no severe population bottleneck has
occurred in human evolution." ~ Francisco J. Ayala, Ananias
Escalante, Colm O'hUigin and Jan Klein, "Molecular Genetics of
Speciation and Human Origins," Proc. Natl. Acad. Sci, USA,
91:pp6787-6794, July 1994, p. 6787-6788.
Note that Ayala says that there has not been time to generate the diversity
of human MHC genes over the past 30 million years. They writes:
"If we assume a mean population size of 10^5 individuals
and a long-term generation time of 15 years, the expected
coalescence for neutral alleles is 6 Myr, which is much less than
the 30 Myr coalescence of the DRB1 alleles. Although the
coalescence estimate has a large variance, it seems that either
our ancestral population was even larger than 10 5 or, as
assumed, balancing selection accounts for the long term
persistence of the MHC polymorphisms. The presence of balancing
selection is supported by the analysis of the DNA sequences of
HLA alleles. In codons specifying amino acids of the PBR,
variation at the first and second positions is significantly
higher than at the third position, and this observation is taken
as evidence that positive selection acts on the first two
positions. Moreover, Hill et al. have shown that MHC
polymorphism may increase resistance to Plasmodium falciparum,
the parasite responsible for malignant malaria.
"Estimates of the magnitude of the selection coefficient, s,
that maintains the MHC polymorphisms vary from locus to locus,
but range from 0.0007 to 0.019. It seems unlikely that the
selection coefficients do not allow for the long-term persistence
of polymorphisms except in the presence of large populations.
For example, only 7 alleles can be maintained in a population of
N=1000, even with overdominant selection as unreasonably large as
0.3." ~ Francisco J. Ayala, Ananias Escalante, Colm O'hUigin and
Jan Klein, "Molecular Genetics of Speciation and Human Origins,"
Proc. Natl. Acad. Sci, USA, 91:pp6787-6794, July 1994, p. 6790.
And some of these polymorphisms date to 70-85 million years ago! O'hUigin
writes:
"The primate DRB loci and allelic lineages exemplify the
consequences of this selection. At the most recent count, 106
alleles can be identified at the DRB1 locus in humans. The fully
functional DRB1 locus is related to the still functional but less
polymorphic DRB3, DRB4 and DRB5 loci as well as pseudogene loci
(DRB2, DRB6,DRB7, DRB8 and DRB9) through a series of ancient
duplications, the oldest predating the divergence of prosimians
and anthropoids about 70-85 MY ago. Alleles at DRB1 can be
subdivided into distinct groups or lineages on the basis of their
sequences and haplotype relationships. Thus the 11 alleles of
the HLA-DRB1*02 lineage are closely related in sequence and
commonly found in conjunction with the DRB5, DRB6 and DRB9 loci.
The 11 alleles of the DRB1*08 lineage are accompanied by the
DRB9 pseudogene alone in the haplotypes where they occur.
Although our knowledge of the genomic organization of non-human
primates is limited, sequence analysis allows the identification
of allelic equivalents for human DRB1 lineages and other DRB1
loci. The presence of most of the DRB1 lineages in Old World
monkeys and apes indicates that the lineages diverged from each
other at least 35 million years ago and possibly earlier. As in
humans, the DRB1 locus is highly polymorphic in non-human
primates and amino acid variability in functional genes is
concentrated at the PBR.
"Despite the long persistence time of alleles, each
mammalian order appears to have a different complement of DRB
genes, Phylogenetic trees based on complete coding sequences of
DRB genes on exon 2 only place all primate lineages on a single
branch together, separate from lineages in ungulates, rodents and
carnivores. Thus in each order the functional DRB lineages
appear to be descended from a different single gene. This
observation places an upper age limit on allelic lineages of
about 90 MY although they may be considerably younger." ~ Colm
O'hUigin, "Quantifying the Degree of Convergence in Primate Mhc-
DRB Genes," Immunological Reviews, 1995:143, p. 123-140, p. 124
The data from the MHC genes are incompatible with the view that mtDNA
represents the original human pair:
"Recent debate, however, has focused attention upon
how accurately the mtDNA data reflects the full
evolutionary history of modern humans. Levels of nuclear
genetic diversity within and between human populations can
be high, especially when compared to our closest primate
relatives. In particular, the very high levels of allelic
diversity for some loci within the Mhc have been viewed as
being incompatible with the relatively small population
sizes inferred from the mtDNA data. There are, for example,
over 100 described alleles each for HLA-B and DRB1 loci in
human populations." Robert E. Hickson, and Rebecca L. Cann,
"MHC Allelic Diversity and Modern Human Origins," Journal
of Molecular Evolution, 45(1997):589-598, p. 589-590
Now, in fairness ot Hickson and Cann, they are right that the mhc data
doesn't support a young humanity but they both believe in mtDNA Eve and are
trying to explain the MHC data away. The thing to note is that they know
MHC is a big threat to their position. It clearly indicates that the common
human pair were NOT within the past 200,000 years, contrary to what all
commonly accepted apologetical positions require.
glenn
see http://www.glenn.morton.btinternet.co.uk/dmd.htm
for lots of creation/evolution information
anthropology/geology/paleontology/theology\
personal stories of struggle
>-----Original Message-----
>From: asa-owner@lists.calvin.edu [mailto:asa-owner@lists.calvin.edu]On
>Behalf Of Brent Foster
>Sent: Tuesday, June 18, 2002 10:43 AM
>To: asa@calvin.edu
>Subject: Breath of life (was Adam, the first man)
>
>
>I have a question for those on the list who know more about
>genetics than I do. In other words anyone. I don’t
>necessarily mean an event where the population is whittled down to
>two breeding individuals. It is certainly a conceivable
>evolutionary scenario that a particular advantageous trait could
>be so advantageous that eventually, over many generations,
>organisms without the trait are completely removed from the
>population leaving no descendants. This could even be imagined in
>Darwin’s day without our current understanding of genetics. But of
>course now we know that observable traits are manifestations of
>genes, and virtually any trait we can think of had its origin as a
>random mutation. And of course if a mutation occurs by random
>chance, chances are it will occur again…and again. So it’s
>extreeeeeemly unlikely that any trait can trace its origin back to
>two, and only two individuals. But suppose the trait we are
>talking about did not originate as a mutation, and suppose that
>trait is the “breath of life”, or the spirit, which God breathed
>into the “first” man. Is it possible to show genetically that all
>human ancestry cannot be traced through two individuals, who were
>the first to have a spirit?
>
>As Wendee said there are different scenarios for the evolutionary
>creationist. To be respectful of the anthropological and
>paleontological evidence we almost have to view Adam as Jim said,
>the first "of the chosen people," but not the first "technical
>human." But it’s interesting to see where this leaves us with
>respect to the question of whether all humans are descended from a
>historic Adam and Eve. Do we all have Adam’s blood in us, or are
>there non-Adamite humans? Whatever the answer, we are all
>certainly Adam’s children in the same sense that all Christians
>are Abraham’s children.
>
>Brent
>
>
>Wendee wrote:
>This isn't what you asked, but, as I'm sure you're aware, there
>are a number
>of different possible scenarios with the first Adam given an evolutionary
>creationist perspective. You give one. Another related but not exactly the
>same is that Adam was the first that evolved Spirit or consciousness. I
>believe that Spirit is obviously spiritual, and consciousness is
>probably an
>evolutionary relict but I see the two as related. In the garden of Eden
>story, it speaks of Adam and Eve as becoming aware of good and evil --
>something I think of as consciousness. In this way, we are different from
>all other created things, and "like God." It could have happened
>in one gene
>mutation, so there could literally have been one literal Adam.
>Personally if
>such a thing did indeed happen, then I believe God was also behind
>it. Such
>is the "punctuated equilibrium" Gould proposed. (ie major evolutionary
>change happening in short periods of time, rather than longer, gradual
>changes). The evolutionary leap to consciousness could have also happened
>more gradually, in which case finding a literal Adam is more difficult.
>Adam could have been a Neanderthal man as I think Glenn proposes, or he
>could have been a modern Homo sapiens or anyone in between. I think its
>important that we don't know, and that there are many possible scenarios
>each with their own theological dilemmas.
>My 0.02, Wendee :)
>
>
>
>
>Brent Foster
>http://home.earthlink.net/~bdfoster/bfpages.htm
>“Blessed are you who weep now, for you will laugh.” - Jesus Christ
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