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Scientists find missing link - and it’s a fish finger
« on: 2008-01-20 17:58:18 » |
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Scientists find missing link - and it’s a fish finger
Source: THe Times
Authors: Brendan Montague
Dated: 2008-01-20
HUMANS could be closer to pond life than had been realised. Researchers have linked a raft of our anatomical and genetic features with fishy ancestors that lived hundreds of millions of years ago.
They have found that the origin of human hands and fingers could lie in the emergence of a finned fish 365m years ago. Similarly, the sophisticated joints that give us the ability to run, grip and turn may owe their existence to a sea creature known as the tiktaalik that lived in the Arctic 375m years ago.
Even our acute vision may be a legacy of an even earlier ancestor, similar to a jellyfish, whose genes have been adapted to play a crucial role in the human eye.
“An entire tree of life, from microbe to worm, to fish and mammal, is embedded inside of us. We can uncover our past by studying fossils and understanding our DNA,” said Neil Shubin, professor of anatomy at Chicago University.
Shubin is about to publish his findings in a book, Your Inner Fish: A Journey into the 3.5 billion-year History of the Human Body, which explores the links between humans and their most ancient forebears.
Shubin’s findings suggest that every bone in the human body first evolved from simple marine ancestors. Our wrists, the unique dexterity of the thumb, even the shape of our skulls, can be traced to origins in primitive sea creatures.
One part of the research involved close examination of a fossilised fish known as a tiktaalik, which was discovered in the Arctic four years ago.
Shubin found that its skeleton displayed rudimentary versions of the human shoulder, elbow, forearm and wrist.
“When we study the structure of these joints to assess how one bone moves against another, we see that tiktaalik was specialised for a rather extraordinary function - it was capable of doing push-ups,” writes Shubin.
Separately, Shubin has found that modern-day fish carry genes allowing for the growth of wrists, hands and fingers. These are now “switched off” so the digits never develop in the fish.
Such findings cast doubt on the assumption that hands are a more recent evolutionary step than fins. Instead, fins may have developed as an improvement on hands.
The research also supports the argument that the majority of the human genome developed 500m years ago and is shared with most living creatures.
One of the factors that makes living forms different is the ability to switch off certain genes while retaining them in the genome.
An alternative approach is to adapt similar genes to different purposes. Some of the genes involved in the evolution of human vision and hearing play an active but very different role in the metabolism of jellyfish.
“The genome has changed a bit, but the similarities greatly outweigh the differences,” said Shubin last week.
Richard Dawkins, author of The God Delusion and professor of the public understanding of science at Oxford University, said the research was a new blow to the Bible’s version of how humankind was created.
“The tiktaalik is an extremely important and exciting find in terms of bridging a gap in our ancestral history between when we lived in water and when we lived on land,” said Dawkins.
“This evidence is what we would expect as evolutionists, but it would be extremely embarrassing for a creationist.”
Shubin said: “Looking back through billions of years, everything innovative or apparently unique in the history of life is really just old stuff that has been recycled, recombined, repurposed or otherwise modified for new uses. This is the story of every part of us.”
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