Teori Darwin telah dibuktikan benar.
Mutasi telah dibuktikan memang terjadi.
Evolusi telah dibuktikan memang terjadi.
Dan boleh dibilang tiap hari para ahli diberbagai bidang menyempurnakan dan
melengkapi teori Darwin itu...
Nggak heran bahwa aklhirnya gereja katolik Roma juga mengakui kebenaran teori
Evolution Of Fins And Limbs Linked With That Of Gills
Gill skeletons. The shark arch gill skeleton (left) shows primitive gill rays
that are found only in sharks and other cartilaginous fishes. The gills of
other fishes (right) are also arched but lack gill rays. This primitive feature
of sharks allowed the researchers to link the developmental genetic program for
fins and limbs to the more primitive one for gill rays. (Credit: Image by J.
Andrew Gillis, University of Chicago)
ScienceDaily (Mar. 25, 2009) — The genetic toolkit that animals use to build
fins and limbs is the same genetic toolkit that controls the development of
part of the gill skeleton in sharks, according to a new study.
The research is published in Proceedings of the National Academy of Sciences on
March 23, 2009, by Andrew Gillis and Neil Shubin of the University of Chicago,
and Randall Dahn of Mount Desert Island Biological Laboratory.
"In fact, the skeleton of any appendage off the body of an animal is probably
patterned by the developmental genetic program that we have traced back to
formation of gills in sharks," said Andrew Gillis, lead author of the paper and
a graduate student in the Department of Organismal Biology and Anatomy at the
University of Chicago. "We have pushed back the evolutionary origin of the
developmental genetic program that patterns fins and limbs."
This new finding is consistent with an old theory, often discounted in science
textbooks, that fins and (later) limbs evolved from the gills of an extinct
vertebrate, Gillis added. "A dearth of fossils prevents us from definitely
concluding that fins evolved from gills. Nevertheless, this research shows that
the genetic architecture of gills, fins and limbs is the same."
The research builds on the breakthrough discovery of the fossil Tiktaalik, a
"fish with legs," by Neil Shubin and his colleagues in 2006. "This is another
example of how evolution uses common developmental programs to pattern
different anatomical structures," said Shubin, who is the senior author on the
PNAS paper and Professor and Associate Dean of Organismal and Evolutionary
Biology at the University of Chicago. "In this case, shared developmental
mechanisms pattern the skeletons of vertebrate gill arches and paired fins."
The research also showed for the first time that the gill arch skeleton of
embryonic skates (a living relative of sharks that has gill rays) responds to
treatment with the vitamin A derivative retinoic acid in the same way a limb or
fin skeleton does: by making a mirror image duplicate of the structure as the
embryo develops. According to the researchers, the genetic circuitry that
patterns paired appendages (arms, legs and fins) has a deep evolutionary origin
that actually predates the origin of paired appendages themselves.
"These findings suggest that when paired appendages appeared, the mechanism
used to pattern the skeleton was co-opted from the gills," Gillis said.
"Perhaps we should think of shark gills as another type of vertebrate
appendage—one that's patterned in essentially the same way as fins and limbs."
The deep structural, functional, and regulatory similarities between paired
appendages and developing gill rays, as well as the antiquity of gills relative
to paired appendages, suggest that the signaling network that is induced by
retinoic acid had a patterning function in gills before the origin of
vertebrate appendages, the research concludes. And this function has been
retained in the gill rays of living cartilaginous fishes.
1. J. Andrew Gillis, Randall D. Dahna, and Neil H. Shubin. Shared
developmental mechanisms pattern the vertebrate gill arch and paired fin
skeletons. Proceedings of the National Academy of Sciences, 2009; DOI:
Adapted from materials provided by University of Chicago Medical Center, via
EurekAlert!, a service of AAAS.
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