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Ontogenetic Depth and Its Relevance One of the most powerful tools against common descent is virtually unknown: ontogenetic depth . This isn't surprising, of course, as it is a relatively new concept. Just the name, though, probably turns off many young (and old?) IDists. I don't presume to know much about it myself, as I have no training in developmental biology, but Paul Nelson has done his best to explain it in various places and I have the basics down. So consider this one of those “written by the layman for the layman”-type pieces. Everyone reading this is probably familiar with the developmental hourglass of Icons fame. If not, go to Amazon.com or the library and get yourself a copy of Icons of Evolution . The short version is that biology textbooks and evolutionists tell us that at the earliest stages of development (from the first fertilized cell, or zygote, to fully-formed organism), different types of organisms (chicken, human, frog, etc.) look very similar. These different types of organisms represent the major animal groups. The problem is that these textbooks and scientists are wrong. Developmental biology tells us that at the earliest stages of development and onward, different types of organisms look very different. What does this mean? The major animal groups are distinguishable from their widely dissimilar developmental programs, differences than extend even to the earliest stages. Now, if common ancestry is true and everything evolved from a single cell, then this means that early organisms on the earth had identical developmental programs. Organism A would reproduce Organism B, but both of their developmental programs would be the same, just as a human baby's development does not defer from the mother's. In other words, since the offspring of those early organisms would inherit those developmental programs, the differences we see in the animal groups at the earliest stages must have evolved through billions of years of developmental mutations slowly affecting those developmental stages. This is where ontogenetic depth comes in. Paul Nelson, senior fellow at the Discovery Institute, and Marcus Ross presented this concept at the Society of Developmental Biology earlier this year. I expect their full poster to be up on ISCID shortly, so will let the poster speak for itself. However, the basic idea has been out in the public sphere for a while (see Nelson's live chat, http://www.iscid.org/paul-nelson-chat.php ). In short, attempts thus far to explain the evolution of development (specifically during the Cambrian explosion, when the various body plans emerged) have proven inadequate. Nelson and Ross propose the concept of ontogenetic depth (from zygote to fertile adult), taking into account a wide range of data, to “measure” this developmental evolution. This measure will enable us to better understand what exactly we're seeing, to recognize how different the various developmental programs of the different animal groups are. Ontogenetic depth becomes useful when you consider how the various developmental programs came to be. How did they evolve? How did human development become so different from frog development? This ties in a related concept called generative entrenchment. Let's suppose an organism's development is represented by a series of dominoes. You must knock over the first stage to get to the second, the second to get to the third, and so forth, until you knock over the last domino (or until you are fully developed into an adult capable of reproduction). If you messed with the domino arrangement, however, you might not ever get to the last domino. If you twisted the second domino in such a way that it fell over flat onto the surface and never touched the third domino, then the rest of the dominos wouldn't be knocked over (or development would not be completed). The earlier in the chain you messed with the dominos the worse the effects would be. The same thing happens with development. It just doesn't want to be messed with (or mutated), because if that happens you end up with a dead, deformed, and/or infertile organism. In other words, development is a conserved process. But that can't be true! The earliest stages of development are different among the various animal groups. They must have evolved somehow. But how? If development can't be touched, how did it change? The simplest answer for IDists is that it didn't. Comments? Contact Tristan Abbey at tabbey@idurc.org. Copyright 2003 idurc.org. All rights reserved. International copyright secured. Click here to return to the Papers Archive
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