I've just finished the book Time Frames by Niles Eldridge. It promotes the theory that evolution occurs more rapidly than previously thought, with periods of little change called "stasis" in between these rapid evolution events. This is opposed to the theory of phyletic gradualism, where evolution occurs very slowly over long periods of time, with very gradual change in species. After completing the book, I realized that I, as well as many of my MFK cohorts, may have evidence of this phenomenon in our living rooms.
The Polypterids are a species of fish that have changed very little over the last 100 million years. Although there are slight differences in size, coloration, and even jaw shape, the Polypterids that we keep in aquaria are quite similar to the fossilized remains of Polypterids from millions of years ago (see photos, the latter being drawn from BeBlondies primer ). Why have they experienced so little change when other species from that era have adapted, changed or died out?
I would posit that the Polypterids are generalized predators as opposed to being specialists. This means that they have a wide variety of foods that they will eat and we can see the evidence for this in aquaria. They will eat shrimp, small fish, dead fish, fish fillets, crabs, frogs, insects, even pellets. They are also obligate air-breathers, meaning that they extract a significant portion of their oxygen by taking gulps of air from the surface. They seem to tolerate varied water conditions rather well. This is opposed to specialist predators that have a highly limited menu of prey species and/or can tolerate only more specific water conditions. Specialist species are more prone to be forced to adapt or die out as environmental changes occur.
In other words, the reason that the Polypterids changed little over the last 100 million years is because they had no reason to undergo massive change, they were already equipped to be a successful species even if environmental changes did occur. Their varied diet and hardiness has allowed them to fill biological niches easily and without much physiological adaption. It could be suggested that this is evidence for evolutionary stasis.
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The Polypterids are a species of fish that have changed very little over the last 100 million years. Although there are slight differences in size, coloration, and even jaw shape, the Polypterids that we keep in aquaria are quite similar to the fossilized remains of Polypterids from millions of years ago (see photos, the latter being drawn from BeBlondies primer ). Why have they experienced so little change when other species from that era have adapted, changed or died out?
I would posit that the Polypterids are generalized predators as opposed to being specialists. This means that they have a wide variety of foods that they will eat and we can see the evidence for this in aquaria. They will eat shrimp, small fish, dead fish, fish fillets, crabs, frogs, insects, even pellets. They are also obligate air-breathers, meaning that they extract a significant portion of their oxygen by taking gulps of air from the surface. They seem to tolerate varied water conditions rather well. This is opposed to specialist predators that have a highly limited menu of prey species and/or can tolerate only more specific water conditions. Specialist species are more prone to be forced to adapt or die out as environmental changes occur.
In other words, the reason that the Polypterids changed little over the last 100 million years is because they had no reason to undergo massive change, they were already equipped to be a successful species even if environmental changes did occur. Their varied diet and hardiness has allowed them to fill biological niches easily and without much physiological adaption. It could be suggested that this is evidence for evolutionary stasis.
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