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Evolution or Creation of the Blind Cave Fish

The Blind Cave Tetra, Astyanax mexicanus is a subspecies of the Mexican Tetra without functional eyes.  In fact, the place the eyes should be is covered by skin. This fish comes from cave systems in Mexico.  People have asked the question: was this fish created for these conditions, or did it evolve.

The Evolutionally Point of View

These cave systems are connected to surface waters, and some Mexican tetras found their way in.  Some of these survived despite the lack of light in the caves.  Of course, the ones which were better able to find food without using their eyes were more likely to survive and these were the ones which bred the next generation.  Small, or big, differences accumulated.  Now the blind cave fish has a better sense of smell than their sighted cousins as well as an improved lateral line sense.

Darwin thought that disuse of an organ by itself would result in the loss of that organ.  Modern genetics casts doubt on this belief, although there is a possible genetic mechanism for this to happen, but there may be advantages from having no eyes to the Blind Cave Tetra.  These include having less brainpower required for interpreting their vision, leaving more for interpreting the inputs from their other senses.

Note that this is not evidence of the formation of a new species, because the Blind Cave fish is still in the same species as the other populations of the Mexican Tetra.


The creationists suggest that this fish was created suitable for these conditions.  Some creationists use the existence of this fish as evidence against evolution.  This is based on the idea that the blind cave fish is a simpler form than the normal Mexican Tetra, and things evolve to more complicated, not to simpler forms.

On this basis, the existence of this sightless fish is certainly evidence against one interpretation of Saint Augustine‚Äôs Theory of Evolution.  However, it is no evidence against the theory of evolution by natural selection proposed by Charles Darwin and Alfred Wallace in the nineteenth century.

There is no reason to expect that all advantageous characteristics will be more complicated than the one they replace.  There are plenty of examples of simple living organisms which are good at surviving. Bacteria have been one of the most successful organisms.

Another successful organism is Duckweed, a tiny flowering plant of the genus Lemna which also appears to be an example of evolution to a simper form.

By JohnstonDJ (Own work)[ GNU Free Documentation License,], via Wikimedia Commons