Why do organisms build tissues they seemingly never use?

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Why, after millions of years of evolution, do organisms build structures that seemingly serve no purpose?


A study conducted at Michigan State University and published in the current issue of The American Naturalist investigates the evolutionary reasons why organisms go through developmental stages that appear unnecessary.

“Many animals build tissues and structures they don’t appear to use, and then they disappear,” said Jeff Clune, lead author and former doctoral student at MSU’s BEACON Center of Evolution in Action. “It’s comparable to building a roller coaster, razing it and building a skyscraper on the same ground. Why not just skip ahead to building the skyscraper?”

Why humans and other organisms retain seemingly unnecessary stages in their development has been debated between biologists since 1866. This study explains that organisms jump through these extra hoops to avoid disrupting a developmental process that works. Clune’s team called this concept the “developmental disruption force.” But Clune says it also could be described as “if the shoe fits, don’t change a thing.”

“In a developing embryo, each new structure is built in a delicate environment that consists of everything that has already developed,” said Clune, who is now a postdoctoral fellow at Cornell University. “Mutations that alter that environment, such as by eliminating a structure, can thus disrupt later stages of development. Even if a structure is not actually used, it may set the stage for other functional tissues to grow properly.”

Going back to the roller coaster metaphor, even though the roller coaster gets torn down, the organism needs the parts from that teardown to build the skyscraper, he added.

“An engineer would simply skip the roller coaster step, but evolution is more of a tinkerer and less of an engineer,” Clune said. “It uses whatever parts that are lying around, even if the process that generates those parts is inefficient.”


continue to source article at scienceblog.com

14 COMMENTS

  1. Successful evolutionary adaptations make species prosper at a faster rate than some of their own tissues that have evolved to be redundant, formerly useful.  We can gauge whether a species has evolved faster therefore reproduced more by certain adaptations, if there is separate redundant tissue. If selfish genes favour the growth of a certain tissue type because it augments self replication then selection will make tissue that no longer partakes in the evolutionary drive useless. Atavistic vestigial tissue cladistically presents a picture of an organism that has branched into an evolutionary line other than its ancestors.

  2. @ BrianMMM
    I think that genes send the instructions to the chains of chemical factories that build tissues.
    Genes can’t build anything – just as a library of recipes can’t make meals – only sending a program that selects specific tools to initiate multi-step processes, which are influenced by other ongoing processes, from which the end result emerges.

     

  3.  
    Andrew Planet, 
    Successful
    evolutionary adaptations make species prosper at a faster rate than
    tissues that have evolved to be redundant, formerly useful.  We can
    gauge whether a species has evolved faster therefore reproduced more by
    certain adaptations, if there is separate redundant tissue

    An interesting example, is the progressive loss of legs in whale evolution.

    he 18-inch-long hind legs of Basilosaurus (left leg, above) were far too small to support the whale’s massive 50-foot-long body. In fact, the creature never left the water. But the retention of legs is dramatic evidence that earlier whales once walked—and ran—on land. No one knows for sure how Basilosaurus used its tiny legs; paleontologist Philip Gingerich believes they may have served as stimulators or guides during copulation. – http://ngm.nationalgeographic…. – (see the last picture in the photogallery series)

    WHALES: FROM LAND TO SEA  – animated diagram – - http://ngm.nationalgeographic….

    Early whales plied the shallows but still hauled themselves onto shore,
    probably to rest and to give birth. The fossil record tracks anatomical
    changes as whales adapted to conditions that favored a fully marine
    mammal. Modern whales appeared about 34 million years ago. Only selected
    whales are shown—these don’t represent a “straight line” in evolution,
    but a sampling of some of the genera that existed.

  4. I think Richard said once on an episode of “Inside Nature’s Giants” that, for example, a tail on a land mammal is a costly investment, so that tail “must do something” to justify its own existence.

    In the case of a monkey, it’s obvious that the tail improves the monkey’s sense of balance and agility as it jumps from tree to tree, giving it certain advantages, while tails have disappeared on hominides such as gorillas, chimpanzees, and, well, us – because we no longer spend most of our time balancing on thin tree branches.

    On the other hand, certain marine mammal species still have remnants of hip bones in their
    bodies which are of no use at all in their environment, and yet, those
    bones haven’t fully disappeared. Maybe developing these extra bones
    isn’t such a costly process as a young marine mammal is growing, and
    therefore nature and evolution have sort of turned a blind eye?

    Could it perhaps be argued that the less costly a specialized tissue is for an organism, the less likely it is to disappear if/when it is no longer needed?

  5. Having recently learnt of the term tachytely at the Calpe 2012 conference, from Ian Tattershell, I’d like to sum up.  The new developmental adaptations involved in tachytely cannibalises the  former phenotypical expressional stance of an organism at a genetic rate faster that other  tissue left redundant, due to a lack of need for development or maintaining.  Talking to Ian, he suggested after proposing to him what I’d written here prior, concerning the recent findings indicating junk DNA perhaps is not all junk DNA, might apply to known vestigial tissue.  I told him I’d work on it for some specific cases and I’ll post it here when I’ve done that.  Incentive affecting my phenotypical expressional stance.  Thanks!

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