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Experimental Evolution

September 15, 2012

This news article on Experimental Evolution came as a surprise to me.  I had been reading about ontogeny and philogeny for some time in Steven Jay Gould’s many books.  To start, I’d better define those terms.  Ontogeny is development of the embryo, whereas philogeny is evolution of the animal.  For a variety of reasons, they should have a general similarity.  Both have the same starting point: a single cell.  They have the same ending point: the animal.  They also have differences.  Development of the embryo does follow a single path.  Evolution is a copiously branching tree, but it’s always possible to trace a single path through the tree structure when the end point is known.  Of course, the time scale is enormously different: months versus millions of years.

The cause is also different.  Evolution is driven by variation within a population of organisms and changes in the environment of this population.  Natural variation occurs randomly.  Environmental changes are unpredictable.  Fetal development, on the other hand,  is controlled by chemicals released by the developing organism.  The apparent similarity between ontogeny and philogeny has led to a great deal of misunderstanding.  Steven Jay Gould has documented this well, along with a  misunderstanding of human evolution that places white European men at the pinacle of evolution.  This all seems unbelievable now, but human children became equivalent to both adult evolutionary ancestors and adults of primitive tribes.  Sigmund Freud traced human disorders back to events that occured during evolution, with fixation at corresponding stages of development.  Dr Down identified a group of patients as Mongoloid because of their supposed resemblence to people from Mongolia.

A key point in the similarity between ontogeny and philogeny is an explanation for features that appear during embryonic developent and later disappear.  Steven Jay Gould has written about some of these.  At one stage during its development, a human embryo has gills.  At another stage, it has a tail.  The news article and the scientific study that it’s based upon addresses this point.  The surprise to me was that the animal used in this study was a self-replicating computer program that could evolve through generations and adapt to environmental pressure.  This study concluded that elements of these features are reused to form other features.  Certainly it’s well known that the gill support bones of a developing mammal become inner ear bones and jaw bones in the adult animal.

The study also described the conservation principle.  The early stages of embryonic development build a foundation.  This includes many basic features.  It’s risky to omit one at that point because that would affect too many  features that develop later.  The embryo likely won’t survive.  Later stages complete the animal.  It’s safer to remove or modify features there because the effects are less widespread.

In reading this study, I realized that the embryonic plan itself is inherited and evolves.  This is a chemical plan, a plan that works.  Ontogeny is actually a part of philogeny.  The correspondence between the two is for entirely practical reasons.  An animal does not climb its own evolutionary tree, as people once thought.

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