

drjamielove At yahoo.com via mol-evol%40net.bio.net (by drjamielove At yahoo.com)
Sun Nov 12 14:14:09 EST 2006

The Robertsonsian fusion that formed human chromosome number two (from
ancestral 2A and 2B, as it is preserved in the other apes) should have
caused a serious reproductive barrier, overcome only by consanguity of
the highest order; mating amongst first-degree relatives.  Any breeding
outside the immediate family would have lead to unacceptable
chromosomal imbalances.
I cannot imagine a scenario in which this fusion (2a and 2b) could have
survived, and become fixed in our species, unless immediately followed
by consanguity in our lineage.

I often mention this paradox to my Genetics students and I have
searched the literature but I have never found a better explanation nor
an incestuous family. Yet it is apparent from the facts (explained
above) that we are.

The explanation that the "complete" chromosome two is ancestral and
have each and independently experienced centromeric breaks, is not
parsimonious and not accepted by experts in evolution. (It might
not very scientific.)

If this fusion occurred recently there should be an excessive amount of
homozygosity (autozygosity) of genes on human chromosome two as
consanguity, the descendants eventually outbreed and the "new"
number two chromosome somehow became fixed in our descendants). I do
not know if anyone has surveyed the SNPs and alleles for these
chromosomal comparisons but such data might allow a molecular clock
method to determine if the event occurred recently (Homo sps) or
farther back in time (Australopithecus sps).

I am not suggesting that this fusion is what makes us human. Indeed, I
doubt that it is. However, maintaining a balanced chromosomal
complement would have provided a strong reproductive barrier. Mating
with someone with the "old" 2A and 2B karyotype would have resulted
in reduced fecundity due to lethal aneuploidy and errors in meiotic
disjunction. We often speak of humanity as having evolved through a
female from the same family. Placed in the context of fairy tales, I
conclude that Adam and Eve were brother and sister or parent and

I look forward to your discussion.


Dr Jamie Love

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