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Study: Structures in life forms have a value even if they don’t do anything


It’s what they don’t do that matters. They don’t disappear, leaving a fatal gap.

In “Why do organisms build tissues they seemingly never use?” (Michigan State University, August 10, 2012), Jeff Clune discusses the question:

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.”

An interesting consequence is that newly evolved traits tend to get added at the end of development, because there is less risk of disrupting anything important. That, in turn, means that there is a similarity between the order things evolve and the order they develop.

The original story is kind of confusing, but it certainly sounds like design, not that they are allowed to say that, let alone believe it – the latter is a far worse offense.

The analogy offered, to a skyscraper replacing a roller coaster, is ridiculous because there is no functional or structural unity between the two artifacts.  The situation is more like  men having nipples because women need them. Embryo development that excluded nipples from the male, with no real benefit, would probably just not make sense.

Here’s the paper.

This paper actually tries to come up with an explanation for the "ontogeny recapitulates phylogeny" idea. In other words, the belief that higher organisms go through some of the same developmental stages as their evolutionary history itself went through (allegedly). They postdict (not predict) that this should happen because early features that work should stick around, and the earlier they develop in the embryo, the more time there is to accrue benefit from them. If they work, they should also be conserved by evolution. First problem is that they only explore the idea via computer simulations of evolution. They have no actual observational/experimental evidence. Seems like the goal should be something like 1) showing that we're not just imagining things, as we have a tendency to see patterns and similarities where there aren't any; 2) show that the same gene(s) are responsible for both the original feature and its recapitulation(s) on down the line; 3) that evolution wouldn't be able to replace old-but-useful structures with newer, simpler ones as time went on. (After all, evolution is supposed to be so good at optimization.) The canonical example of this idea is gill slits in human embryos. The question should be whether the same gene(s) that are responsible for gills in fish are the same ones that produce the "slits" in human embryos. If they aren't the same--and at the same location in the genome, etc., then all bets should be off. I'm not a geneticist, but haven't run across claims of a genetic sort to back the evolutionist's position. Sounds like more wishful evolutionist thinking to me... EDTA

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