Turning Fins Into Hands

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Your hands are, roughly speaking, 360 million years old. Before then, they were fins, which your fishy ancestors used to swim through oceans and rivers. Once those fins sprouted digits, they could propel your salamander-like ancestors across dry land. Fast forward 300 million years, and your hands had become fine-tuned for manipulations: your lemur-like ancestors used them to grab leaves and open up fruits. Within the past few million years, your hominin ancestors had fairly human hands, which they used to fashion tools for digging up tubers, butchering carcasses, and laying the groundwork for our global dominance today.


We know a fair amount about the transition from fins to hands thanks to the moderately mad obsession of paleontologists, who venture to inhospitable places around the Arctic where the best fossils from that period of our evolution are buried. (I wrote about some of those discoveries in my first book, At the Water’s Edge.)

By comparing those fossils, scientists can work out the order in which the fish body was transformed into the kind seen in amphibians, reptiles, birds, and mammals–collectively known as tetrapods. Of course, all that those fossils can preserve are the bones of those early tetrapods. Those bones were built by genes, which do not fossilize. Ultimately the origin of our hands is a story of how those fin-building genes changed, but that’s a story that requires more evidence than fossils to tell.

A team of Spanish scientists has provided us with a glimpse of that story.  They’ve tinkered with the genes of fish, and turned their fins into proto-limbs.

Before getting into the details of the new experiment, leap back with me 450 million years ago. That’s about the time that our early vertebrate ancestors–lamprey-like jawless fishes–evolved the first fins. By about 400 million years ago, those fins had become bony. The fins of bony fishes alive today–like salmon or goldfish–are still built according to the same basic recipe. They’re made up mostly of a stiff flap of fin rays. At the base of the fin, they contain a nubbin of bone of the sort that makes up our entire arm skeleton (known as endochondral bone). Fishes use muscles attached to the endochondral bone to maneuver their fins as they swim.

Our own fishy ancestors gradually modified this sort of fin over millions of years. The endochondral bone expanded, and the fin rays shrank back, creating a new structure known as a lobe fin. There are only two kinds of lobe fin fishes left alive today: lungfishes and coelacanths. After our ancestors split off from theirs, our fins became even more limb like. The front fins evolved bones that corresponded in shape and position to our ulna and humerus.

Written By: Carl Zimmer
continue to source article at blogs.discovermagazine.com

10 COMMENTS

  1.  ” A team of Spanish scientists has provided us with a glimpse of that
    story.  They’ve tinkered with the genes of fish, and turned their fins
    into proto-limbs. “

    I have tried to explain this HOX gene ” magic ” to creatards and have been met by blank stares, blustering and a continuation of their never ending fallacies. It is worse than trying to explain  polyploidy in plants to creationists. With polyploidy they seem to intimate an understanding until the ideology kicks in, but the findings of evo devo are truly magic to them and totally beyond their understanding.

  2. It is interesting to look at living fossils and convergent forms of evolution:

      Coelacanths ( /ˈsiːləkænθ/, adaptation of Modern Latin Cœlacanthus “hollow spine”, from Greek κοῖλ-ος koilos “hollow” + ἄκανθ-α akantha “spine”, referring to the hollow caudal fin rays of the first fossil specimen described and named by Louis Agassiz in 1839[1]) are members of an order of fish that includes the oldest known living lineage of Sarcopterygii (lobe-finned fish and tetrapods). – http://en.wikipedia.org/wiki/C

    Some of these are very good for debunking incredulity about fins developing for walking.

      Mudskippers are members of the subfamily Oxudercinae (tribe Periophthalmini),[1] within the family Gobiidae (Gobies). They are completely amphibious fish, fish that can use their pectoral fins to walk on land.[2][3] Being amphibious, they are uniquely adapted to intertidal habitats, unlike most fish in such habitats which survive the retreat of the tide by hiding under wet seaweed or in tidal pools.[4] Mudskippers are quite active when out of water, feeding and interacting with one another, for example to defend their territories. – http://en.wikipedia.org/wiki/M

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

  3.  …hence their constant demand for examples of intermediates in the fossil record…

    Save the first, all lifeforms in the fossil record and to date are intermediate. Becoming intermediate is a prime objective in evolutionary development.

    I tried a few years ago to explain to a creationist speciation through polyploidy with the well documented example of Townsend’s Cord Grass (Spartina x townsendii). His response was “well, it’s still just a grass!”. A major part of their learning difficulty seems to be an inability to deal with large orders of magnitude of both time and space and the inverse of that, with glacially gradual change.

  4. – Geoff 21

     …hence their constant demand for examples of intermediates in the fossil record…

    Save the first, all lifeforms in the fossil record and to date are intermediate. Becoming intermediate is a prime objective in evolutionary development.

     

    YECs could be considered and intermediate form, or evolutionary throwback, between shoaling fish and scientific intellectuals!

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