Re: Sharks, Humans Share Genetic Kinship

I have to say that Van Sommeran's comment is one of the sillier ones I
have seen. I suspect he hasn't looked much into molecular genetics.
Silly even without molecular genetics. example:

Van Sommeran's
He added, "Sharks copulate like mammals and females give birth to live
young, so sharks do have features in common with mammals. It makes
sense that these would show up in the genome."

The way sharks give birth live are physiologically and
anatomically different from the way mammals give birth live, and they
develop different even from the way nonmammilian amniotes develop.
Sharks do not have an amniote sac, they do not have a placenta, and
they do not gain nourishment by attachment to the mothers circulatory
system. Generally, shark embryos absorb nourishment from their gills.
The shark embryo swims freely through the womb, and the gills absorb
from the surrounding fluid. Mammals do no absorb nourishment through
their pharyngeal slits (the homolog to gills). They are attached
directly to the circulatory system. The shark "womb" is not anything
like a mammilian uterus.
Shark embryos develop rapidly, and occassionally eat one another
while still in the mothers "womb." There is no implantation in most
sharks. No such direct conflict occurs in mammalian embryos (yes, I
know there are some sneaky ones).
Sharks do not copulate like mammals, at least not in terms of
anatomy. The males use a pair of pelvic fins to copulate. The pelvic
fins do not have any internal resemblance to the mammalian penis. The
pelvic fins have an anatomical resemblance to mammilian legs, though.
They have bones and joints. They are used a little bit for swimming
(or maybe steering). There are grooves in the shark's pelvic fin that
guide the semen. The amniotes including mammals have a tube that is
actually a modification of a tube used by the renal system. Some
mammals have a dermal bone that stiffens their penis. It is unjointed,
and does not share any developmental or anatomical resemblance to the
pelvic fin.
The reproduction function of some sharks to mammals, in the same
way the transportation function in dolphins resembles that of sharks.



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