By: David Bloomberg Re: Eye Evolution From the State JournalRegister (Springfield, IL), 11
By: David Bloomberg
Re: Eye Evolution
From the State Journal-Register (Springfield, IL), 11/6/94:
Evolution in the blink of an eye
by Carol Yaesuk Yoon
N.Y. Times News Service
One of the most fascinating yet awkward problems that have challenged
biologists since Charles Darwin is how to explain the evolution of complex
structures such as the eye and the wing. How does a blind force like natural
selection sculpt from almost nothing a supremely delicate mechanism such as the
inner structure of the ear?
The trick, so hard to understand, is one that apparently gives evolution no
bother. The eye, for instance, is an organ that has evolved not once but
perhaps dozens of times, since insects, octopuses, mammals and other groups all
have eyes of quite different structure.
Scientists studying how the trick is accomplished at the level of genes and
their protein molecules say they are finding a common thread in this varied
tapestry: evolution produces the strikingly new by tinkering with the old.
Animals do not evolve whole new suites of genes and proteins to build
complex structures. Instead a species appears to construct useful new features
by adapting existing molecules to new uses.
"We're now beginning to provide some answers to the questions Darwin
raised," said Dr. Margaret McFall-Ngai, a developmental biologist at the
University of Souther California at Los Angeles and one of the speakers
discussing the evolution of novelty at a meeting on development and evolution
last week at Indiana University in Bloomington. "We're finding that the
organism is extremely resourceful. It has a set of cards to play and it can
deal them up a bunch of different ways to come up with novel structures. It's
changing our ideas about how these structures are formed."
Dr. Rudy Raff, director of the Institute for Molecular and Cellular Biology
at Indiana University and an organizer of the symposium, said: "The most
surprising and important discovery is the sameness. You see the same genes
used again and again, always co-opted for other uses. If you just take what
you have and reorganize it, you can make something new rather quickly, and I
think that's the way evolution works. And that's one of the surprising things
molecular biology has really revealed.
The puzzle of how an organ as exquisitely complex as an eye could first
evolve was problematic enough that Darwin felt compelled to discuss it at
length in his book "The Origin of Species" in a chapter entitled "Difficulties
of the Theory."
"It's the problem of the incipient stages of useful structures," said Dr.
Stephen Jay Gould, an evolutionary biologist at Harvard University who was the
keynote speaker at the meeting. "We can all see what wings are for when
they're complete wings. But just a few percent of a wing, what good is that?
Darwin's general answer is that it must exist for other purposes, and that
continues as the key theme in the evolution of novelty. You can't get
complexity out of nowhere."
And indeed you don't, as researchers at the National Institutes of Health
studying eye lenses are discovering.
The lens is a remarkable transparent structure filled with proteins called
crystallins, which have been an object of study for more than a century. Found
in great quantities in the lens and perfectly arranged to focus light,
crystallins were long thought to be highly specialized lens proteins that
evolved solely to allow animals to see.
But as researchers studying these proteins are discovering, the evolution
of the lens may have been a lot simpler than was imagined and may begin to
provide lessons in how such complex structures arise in general.
"The story in lens shows that you can evolve complex body parts by
borrowing specialized proteins that are being used for one function for use in
an entirely different function," said Dr. Joram Piatigorsky, chief of the
laboratory of molecular and developmental biology at the National Eye Institute
in Bethesda, Md., and a speaker at the meeting. "I'd rather expect that
similar kinds of things are going on everywhere."
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