16 SEP 2011 by ideonexus
Mammals Produce Useless Yolks
Vestigial genes can go hand in hand with vestigial structures. We
mammals evolved from reptilian ancestors that laid eggs. With the
exceptions of the “monotremes” (the order of mammals that includes
the Australian spiny anteater and duck-billed platypus), mammals have
dispensed with egg-laying, and mothers nourish their young directly
through the placenta instead of by providing a storehouse of yolk. And
mammals carry three genes that, in reptiles and birds, produce the
nutritious protein...
1 Because they evolve from egg-laying reptiles, they have dead genes for producing yolks and even produce yolks in the placenta.
16 SEP 2011 by ideonexus
Ontogeny Recapitulates Phylogeny
Now, we’re not absolutely sure why some species retain much of their
evolutionary history during development. The “adding new stuff onto
old” principle is just a hypothesis—an explanation for the facts of embryology.
It’s hard to prove that it was easier for a developmental program
to evolve one way rather than another. But the facts of embryology
remain, and make sense only in light of evolution. All vertebrates begin
development looking like embryonic fish because we all descended... 1 
notes
notesEmbryos go through the stages of the evolution of their ancestors as they develop.
16 SEP 2011 by ideonexus
Dolphins have Genes for Smelling
Another curious tale of dead genes involves our sense of smell, or
rather our poor sense of smell, for humans are truly bad sniffers among
land mammals. Nevertheless, we can still recognize over 10,000 different
odors. How can we accomplish such a feat? Until recently, this was a
completely mystery. The answer lies in our DNA—in our many olfactory
receptor (OR) genes.
[...]
Our own sense of smell comes nowhere close to that of mice. One
reason is that we express fewer OR genes—only abou... 1 notes
notesYet, as aquatic mammals, they have no need to smell anything.
16 SEP 2011 by ideonexus
Vestigial GLO Pseudogene
And the evolutionary prediction that we’ll find pseudogenes has been
fulfilled—amply. Virtually every species harbors dead genes, many of them still active in its relatives. This implies that those genes were also
active in a common ancestor, and were killed off in some descendants but
not in others. Out of about 30,000 genes, for example, we humans carry
more than 2,000 pseudogenes. Our genome—and that of other species—
are truly well populated graveyards of dead genes.
The most fam... 1 notes
notesUsed to produce Vitamin C, alive in most mammals, but dead in humans, primates, and others.
16 SEP 2011 by ideonexus
Hen's Teeth
Some atavisms can be produced in the laboratory. The most amazing
of these is that paragon of rarity, hen’s teeth. In 1980, E. J. Kollar and
C. Fisher at the University of Connecticut combined the tissues of two
species, grafting the tissue lining the mouth of a chicken embryo on top
of tissue from the jaw of a developing mouse. Amazingly, the chicken
tissue eventually produced tooth-like structures, some with distinct roots
and crowns! Since the underlying mouse tissue alone could not prod... 1 notes
notesAn experiment from 1980 that stimulated hens to grow teeth by triggering a gene holdover from their ancient reptilian ancestors.
16 SEP 2011 by ideonexus
Vestigial Traits in Humans
Our bodies teem with other remnants of primate ancestry. We have a
vestigial tail: the coccyx, or the triangular end of our spine, that’s made
of several fused vertebrae hanging below our pelvis. It’s what remains
of the long, useful tail of our ancestors. It still has a function
(some useful muscles attach to it), but remember that its vestigiality is
diagnosed not by its usefulness but because it no longer has the function
for which it originally evolved. Tellingly, some humans have a r... 1 notes
notesRemnants of a tail, muscles that serve no purpose, etc.
16 SEP 2011 by ideonexus
Clarification of the Term "Vestigial"
Opponents of evolution always raise the same argument when vestigial
traits are cited as evidence for evolution. “The features are not
useless,” they say. “They are either useful for something, or we haven’t
yet discovered what they’re for.” They claim, in other words, that a trait
can’t be vestigial if it still has a function, or a function yet to be found.
But this rejoinder misses the point. Evolutionary theory doesn’t say
that vestigial characters have no function. A trai... 1 notes
notesA trait is vestigial not because it no longer serves a purpose, but because it no longer serves its original purpose.
20 MAY 2011 by ideonexus
Our Sinuses are Upside Down
Another consequence of our own shift from quadruped to biped concerns the sinuses, which
give such grief to many of us (including me at the moment of writing) because their drainage hole is
in the very last place a sensible designer would have chosen. Williams quotes an Australian
colleague, Professor Derek Denton:* 'The big maxillary sinuses or cavities are behind the cheeks on
either side of the face. They have their drainage hole in their top, which is not much of an idea in
terms of using... 1 notes
notesLike back pains, its a product of our former quadrupedal nature.
