Icefish and Other Genetic Anomalies and an Argument for Vestigiality

Abstract

If one watches the embryonic development of a mammal, say a mouse, one sees a gradual increase in complexity as a single cell multiplies and develops into tissues and organs. But it does so in steps. The heart, for example, rather than forming as an intact entity begins as a blood vessel that folds to form two distinct chambers, which are characteristic of the heart of a fish. One of the chambers then divides into two so that three are present, which is much like the heart of reptiles. Finally, the undivided chamber is partitioned so that the four chambers characteristic of a mammalian heart finally form. The process appears to be one of adding complexity to simpler, previously developed structures. In fish, blood vessels run from the heart to the gills where carbon dioxide is exchanged for oxygen. Those blood vessels exist in mammals early in development, but they become modified to carry blood from the heart to the head, arms, lungs ,and trunk as development proceeds. From the construction point of view, this is not the most efficient way of doing things; it is analogous to build a diesel locomotive by first building a steam engine and then re-engineering it into a diesel by using the original materials and reworking them. Conceivably, you could end up with something that functions, but it would be far more reasonable to simply build the diesel in the first place. Biologically speaking, however, what is efficient from a constructive point of view is not what we have, and what we have makes sense in terms of evolution. Fish preceded mammals by around 200 million years. As fish spreads through the marine and aquatic niches available to them, some ventured into shallow areas where they were exposed to air for periods of time. Those that could survive in that environment prospered. Over time, modification of their existing structures allowed taking better advantage of this new, oxygen-rich resource that served them well.