I am going to Spain in a
few days for the Cell Symposium on Human Evolution on March 16-18th to present
a poster as shown below (my lab website has a better resolution file for download, http://www.sklmg.edu.cn/articles_98.shtml?l=en-us. The introduction and main conclusions, as copied from
the poster, is in the following.
A common
difficulty for all existing models of human evolution has been to account
for the unusual diversity and admixed
features of the Australian aborigines (AUA). A list of morphological features
aimed at defining modern humans would exclude both modern AUA and Neanderthals,
indicating some shared traits between the two. Fossil studies lack fine
resolution power and molecular studies have yet to produce even just an
internally coherent model uniting autosomes, Y chr, and mtDNA, let alone
consistency with fossils/phenotypes and common sense. Almost every ancient DNA
finding has been a surprise to the existing models, the latest being the 400K
year old Heidelbergensis.
Molecular
studies have so far relied on the Neutral theory and its infinite sites
assumption. The Neutral theory was originally inspired by the so called
molecular clock which was in turn inspired by the first and most remarkable
result in molecular evolution, the genetic equidistance result that sister
species are approximately equidistant to a simpler outgroup. In recent papers,
we have shown that the equidistance result has been incorrectly interpreted by
the molecular clock with grave consequences on phylogenetic studies: nearly all
past studies have used non-informative DNAs assumed to be neutral but have now
been shown by us to be under selection. We have developed the maximum genetic
diversity (MGD) hypothesis to absorb and supersede the neutral theory. From
this more correct/complete theoretical perspective that has coherently
accounted for all major known observations, we developed new methods and
studied the origins of humans using the 1000 genomes project and other public
data.
We found direct
evidence of higher MGD or lower purifying selection for African San and Pygmy
specific Y chr that will dramatically rewrite Y phylogeny. Certain regions of Y
with low contents of repetitive DNAs have few SNPs in all Y haplotypes except
being highly variable in A and B. But in other regions, similar degrees of
variations are found for all haplotypes. Thus, the apparent deep separation or
distance between A and B or between A/B and other haplotypes is not related to
time as is commonly assumed. San/Pygmies have more positions in their genomes that
when mutated are not deleterious to their physiology, which creates higher MGD
and in turn higher innate or natural adaptive capacity required for a primitive
life style.
Two types of
DNAs are a priori informative to phylogenetic studies: slow evolving neutral
DNAs from autosomes are informative to separation time and functional DNAs from
mitochondria (mt) and Y chr are informative to shared internal physiology.
Non-informative to phylogeny but informative to adaptation to outside
environments are the fast evolving DNAs (speed is essential for quick
adaptation to fast changing environments). We verified the informative nature
of different SNPs by testing whether autosomes can reveal the known admixture
history of Mexicans (MXL): those with R1b3 Y haplotype should have relatively
more European and less Chinese autosomes than those with Q haplotype; those
with B2 mtDNA should be the closest to the autosomes of B2 Northern Chinese.
The slow evolving SNPs gave the expected result while all other autosome SNPs
produced only senseless results.
Integrating
autosomes, Y and mtDNA, we found just two original branches of humans,
Europeans with R1a Y chr and U2 mtDNA and Africans with B and L1c, with a
conservatively estimated split time of 2.1 million years. All other Y or mt
branches originated by admixture and adaptive co-evolution as evidenced by
autosomes data. We found a farmers-associated SNP3010 with highest frequency in
D4 Chinese and what may be gene conversions in mtDNA in admixed humans (data
not shown due to space limitations). Southern Chinese (CHS) O2 Y-chr and B2
mtDNA were the oldest or least admixed Asian group and derived from admixture
of R1a/U2 Europeans and B/L1c Africans before leaving Africa for Asia.
Heidelbergensis, Denisovans, and Neanderthals were descendants of a more recent
interbreeding event in Iberia between migrating Africans and local Europeans,
who then moved across Eurasia and became direct ancestors of AUA. These results
suggest a unified hybridization model consistent with physical/cultural traits
and fossil records, which explains the wide diversity of Australian aborigines.
Since the original branching of two groups, further diversification of humans
occurred largely by repeated cycles of migration/hybridization followed by
independent evolution followed by further migration/hybridization, an
intuitively expected pattern if homo has been a single species since the first co-appearance
of H. habilis and H. rudolfensis.
Posts
