Re: Sharks, Humans Share Genetic Kinship

"rmj" <glenna@xxxxxxx> wrote in message
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"Peter Pan" <peterpan55555@xxxxxxxxx> wrote in message
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http://dsc.discovery.com/news/2007/05/21/sharkancestry_ani.html?category=animals&guid=20070521103030&dcitc=w19-502-ak-0000

"Four hundred and fifty million years ago, sharks and humans shared a
common ancestor, making sharks our distant cousins.

As are all other living things. Many are much closer kin than sharks.

According to
recent research, this kinship is evident in our DNA, since at least
one shark species possesses several genes that are nearly identical to
those in humans.

It's not even a shark at all, but a species of chimaera [a separate
group of odd-looking cartilaginous fish].

http://en.wikipedia.org/wiki/Chimaera

The elephant shark's genome is so similar to ours that we wind up
having more in common with it - genetically speaking - than with other
species, such as teleost (bony skeleton) fishes, which are nearer to
us on the evolutionary tree.

Which isn't that suprising, since it's easily possible that [some]
teleosts have changed more in these particular features since the
last common ancestor of bony fish, land vertebrates, and
cartilaginous fish.

And is this claim about teleosts in general, or just certain
specific ones like say pufferfish with their highly modified
genomes?
What about the other, non-teleost, bony fishes?
In particular, what about lungfish and coelacanths, which are
closer kin to land vertebrates than to other bony fish?

"This was a surprising finding, since teleost fish and humans are more
closely related than the elephant shark is to humans," lead author
Byrappa Venkatesh told Discovery News.

Only if you wrongly assume that "have a more recent common ancestor"
necessarily means "are more similar in all ways". It needn't be the
case.

Venkatesh, principal investigator at the Institute of Molecular and
Cell Biology in Singapore, and his team determined that sets of genes
on chromosomes, as well as actual genetic sequences, are "highly
similar in the elephant shark and human genomes."

But doubtless not more similar than many other pairwise comparisons.

The researchers not only analyzed the elephant shark genome, but also
the genes for other animals including pufferfishes, chickens, mice and
dogs.

And? Did the writer want to leave the false impression that these
other tetrapods aren't as close or closer genetically to humans
as the "shark" is?

Their findings were recently published in the journal PloS Biology.

The researchers identified 154 genes in humans that have comparable
matches in mice, dogs and elephant sharks.

Note that this doesn't imply exclusivity. How many of them are
recognizably present in all of the descendants of the mammal/shark
last common ancestor? Note also that "have comparable matches"
seemingly means only that homologous genes can be identified, not
that they are especially similar.

The similarities between
people, mice and dogs were not unexpected, given that they are all
mammals. Sharks, however, are cartilaginous fish that seem to bear
little physical resemblance to mammals.

Except for all the many things that the whole jawed-vertebrate group
shares.

Upon closer examination, sharks and humans do share certain
physiological and biochemical processes.

Well, duh. So do all other living things.
But no doubt there are many much more specific shared features of
the group of descendants of the "shark"/land vertebrate last common
ancestor that can be discussed.

[snip]
"The researchers also found that shark and human immune systems are
very similar, since sharks have all four types white blood cells found
in mammals.

And how widespread are they among the other groups derived from
the "shark"/mammal last common ancestor?

Sean Van Sommeran, executive director of the Pelagic Shark Research
Foundation in Santa Cruz, Calif.,

An administrator who doesn't know much science perhaps? Or perhaps
the reporter turned his actual comments into something much sillier
than they once were? It happens a lot in science reporting.

told Discovery News that he was not
entirely surprised to learn about the shark-human links.

"The field of genetics is a Pandora's box," Van Sommeran said.

He added, "Sharks copulate like mammals and females give birth to live
young,

Neither claim is true for "elephant sharks" [they're egg layers] and
live bearing is not even present in all true sharks. Many lay eggs.

Internal fertilization is clearly independently derived in
cartilaginous fish and land vertebrates [and in some bony fish
and in some amphibians], and that in any fishes doesn't resemble
copulation in mammals in detail.

so sharks do have features in common with mammals. It makes
sense that these would show up in the genome."

That's embarrassingly foolish, since they're not similar traits at all,
and the superficial similarities that exist were independently derived.

Venkatesh said future studies on the elephant shark genome, which is
relatively small and easy to study, could reveal information about
human genes, such as how the immune system develops.

Comparative studies in general, presumably, not just comparisons
with this one species of fish. Scientific press releases are
often pretty bizarrely garbled.

Since sharks are
the oldest living jawed creatures with a backbone,

That's a silly thing to say, since all modern living things are
really equally "old" . Still, "sharks" are an older separate
lineage than most other groups of extant vertebrates.

http://tolweb.org/Gnathostomata/14843

studies on them may
even uncover how humans and other mammals evolved.

That is also a silly thing to say; he might as well claim that
more detailed studies of _Homo sapiens_ should be done to help
understand the evolution of chimaeras.

Comparative studies and cladistic analyses of traits of the whole
group of descendants of the chimaera/mammal last common ancestor on
the other hand should tell us a lot about the whole group and its
various branches.

This is a kick in the teeth for those who believe natural selection and
drift are sufficient explanations for the course of evolution.

No, it's not. Why should it pose any problem at all?

cheers


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