I believe that pretty much everybody has wonder at the weird animals that lives in the depth of the sea. They have those weird shapes, big eyes, long teeth… some have lights of their own, some have fins that look more like legs. You need not to be a biologist to be fascinated by the diversity and otherness of those animals, living in an area that we will never inhabit, or even reach without a great deal of technology. That diversity, actually, is not only fascinating for people outside biology. In a recently published paper (The deep sea is a hot spot of fish body shape evolution, Martinez et al, 2021) the different shapes of these animals are placed in an evolutionary context. As it turns out, the deep sea is what we call an evolutionary hotspot, a place where evolution is happening at rates much higher than anywhere else. It is kind of funny to think that the first hot place that I heard about was London, a city not quite in the bottom of the sea. where the impact of pollution due to the industrial revolution drived evolutionary change in the coloration of moths. That was something that we could see, and influence. Not the bottom of the sea.
When talking about evolutionary hotspots, one must mention the African lake Malawi. In that lake hundreds of species of tiny fishes have appeared in a very short (geological) time. The diversity is easy to grasp, since those tiny fishes are fairly colorful, and even at the shallows of the lake one could see with the bare eye schools of fishes with many different color patterns, not to mention the ones that live beyond our eye. It has been said that the species living in this lake are the 10% of all the species of fresh water fishes. The current explanation is that in geological time the lake Malawi has gone across alternating periods of shallow (producing murky waters) and deeper stages (with crystalline waters). The idea is that in periods of shallow and murkiness the fishes retreated to the rivers that feed the lake, to come back to the lake when refilled, became crystalline, and diverge very fast. In the past 400000 years, the lake has dried three times. Yet all these fascinating Malawi fishes seems to be endangered by increasing human pollution and overuse of the lake’s water. Humans are bringing another period of murky shallow waters, in a scale of time impossible to match by evolutionary processes. Some authors project that since 1980 50% of the diversity has been lost, before being even described. We humans are, literally, destroying an evolution hotspot.
Which brings me back to the deep sea, and the other fishes that are evolving at speeds comparable to a japanese horror movie (well, likely slower). I said that we can not reach those deeps without complex technology, and that is true. I should know, having dived for the last 40plus years, not yet having been deeper than 70 meters and knowing that there is practically no chance for me to ever see this environment, other than by the eyes of a camera. But of course, that is not the only way we have to reach those deeps. Pollution, plastic pollution, mining, and other forms of human intervention are there, already.
How long is going to take for us to realize that we are screwing that system too?