Darwin Was Right

Or at least his grandson was. Apparently, one of the younger Darwin's ideas was that the movement and mixing of water between the equator and poles is influenced by sea life, who swim through the water. This was an idea that was largely ignored until recently. As a report appearing in PhysOrg notes:

Using a combination of theoretical modeling, energy calculations, and field observations, researchers from the California Institute of Technology (Caltech) have for the first time described a mechanism that explains how some of the ocean's tiniest swimming animals can have a huge impact on large-scale ocean mixing.

The idea was largely discarded because it was felt that the movement of the ocean would overwhelm any movement that was made by the fish. Not so, they say:"

Darwin's grandson discovered a mechanism for mixing similar in principle to the idea of drafting in aerodynamics," Dabiri explains. "In this mechanism, an individual organism literally drags the surrounding water with it as it goes."

Using this idea as their basis, Dabiri and Katija did some mathematical simulations of what might happen if you had many small animals all moving at more or less the same time, in the same direction. After all, each day, billions of tiny krill and copepods migrate hundreds of meters from the depths of the ocean toward the surface. Darwin's mechanism would suggest that they drag some of the colder, heavier bottom water up with them toward the warmer, lighter water at the top. This would create instability, and eventually, the water would flip, mixing itself as it went.

This has tremendous implications for evolutionary development. The movement of ocean currents has a large effect on continental temperatures which, in turn, has a large effect on the kinds of vegetation that grow and the kinds of fauna that live there. For example, it is likely that the expansion of the Mediterranean during the Miocene led to cooler temperatures in North Africa, specifically the Afar triangle. This led to reduction in forests and an increase in savannas. A group of late Miocene apes began to exploit the forest fringe area and established their own niche—these became the early hominids. I will be curious to see how this research pans out.


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