From Britain’s Daily Telegraph
Scientists at McGill University have discovered that fish change their anatomy and learn to walk more efficiently when kept out of water for a prolonged period in a discovery that hints at how ancient species evolved to walk on land.
The researchers kept polypterus, an African fish with lungs, on land for eight months (they would normally gravitate back to water).
In less than a year, they found that the fish had learned to walk more efficiently, placing their fins closer to their bodies and lifting their heads higher. They had also learned to move without slipping.
Even their skeletons had adapted around the shoulders, becoming stronger and elongated to increase support during walking and deal with the loss of support from the water.
“There were anatomical changes that resembled the same key evolutionary changes that are seen in the tetrapods that moved into land.”
After 8 months, the terrestrially raised bichir [polypterus] had a more sophisticated style of walking than did aquatically raised controls. Furthermore, their bone structure and musculature changed to be more suited to a walking lifestyle.
The results provide evidence for developmental plasticity, in which organisms alter their anatomy and behaviour in response to environmental change. The team suggests that this process, as demonstrated by the bichir, could have given the earliest tetrapod ancestors the ability to venture onto land. In doing so, claims Standen, they would have become exposed to the selective pressures of a terrestrial environment, thereby speeding up the evolutionary transformation from fins for swimming into limbs for walking.
Maybe. But if they are that plastic, wouldn’t they just go back to the water, given a chance?
David A. DeWitt, biology and chemistry chair at Liberty University, writes to say,
This is not evolution! It has absolutely nothing to do with evolution. There is nothing that is heritable here:
“After 8 months, the terrestrially raised bichir had a more sophisticated style of walking than did aquatically raised controls. Furthermore, their bone structure and musculature changed to be more suited to a walking lifestyle.
The results provide evidence for developmental plasticity, in which organisms alter their anatomy and behaviour in response to environmental change. The team suggests that this process, as demonstrated by the bichir, could have given the earliest tetrapod ancestors the ability to venture onto land. In doing so, claims Standen, they would have become exposed to the selective pressures of a terrestrial environment, thereby speeding up the evolutionary transformation from fins for swimming into limbs for walking.”
They are not talking about natural selection, they are talking about behavioral plasticity. This is a fancy way of saying ‘learned behavior’. The fish that were raised in a terrestrial environment improved their walking ability. Also, although they say that the “organisms alter their anatomy and behavior” it would be more accurate to say that “their behavior altered their anatomy.” This is not the way that we usually think about such things, but that is what happens. The fish did not will themselves to have different anatomy. However, as they used certain muscles in particular ways, those muscles grew stronger. As the muscles grew stronger, they put different mechanical pressures on the bones. The shape of the bones were altered in response to the different mechanical pressures.
See, people intuitively (and falsely) believe that bones are not malleable, that they take a particular shape and that is it. Were it so, we would not be able to grow. The fact is that bone cells continually turn over, but less so as we age. Mechanical pressure will significantly alter how the bone cells divide and therefore over time will alter the shape. Anyone who wears glasses has a way to prove it. Where the frame of the glasses make contact with the skull behind the ears there will be slight depressions. When you get a different pair of glasses, it won’t exactly match, but over time the location of the depression will move.
Here is another example: Babies are born flat footed. As they begin to walk, the arch of the foot develops. The shape of the bones and the way the muscles connect alters in response to the forces and pressures of upright walking. This happens automatically and it is because of how the bone cells respond to mechanical pressure. There is not a gene that produces an arched foot, it is a developmental response to behavior.
Notice what they did not do: they did not select for fish that walked better. The individual fish themselves improved in their walking ability through learning and as they used muscles repeatedly in different ways those muscles grew stronger and as a result, there were changes in bone morphology. No natural selection here. How long did it take? Less than 1 generation.
Standen assumes that natural selection in fact favoured such fish back in the Devonian. We don’t know for sure unless we have some idea what the advantage might be. One problem is that she must have fed and protected the fish during the course of the experiment, something nature is markedly less likely to do. Also, what about egg laying? A fish that could not get back to water, could not lay eggs, and either the line would die out or the plasticity would reverse itself.
What this experiment mainly shows is how fish can become more terrestrial without any evolution, provided they cannot get back to the water. But could they feed and protect themselves on land indefinitely back then? This particular fish has markedly failed to abandon the water, left to itself. Interesting experiment, for sure.
See also: Early tetrapod (“fishapod”) sheds light on transition to land— maybe (Tiktaalik)
Have we at last solved the question of how sea creatures moved to land? (Pacific leaping blenny, which also never really abandoned the water)
Follow UD News at Twitter!