Coelocanth:
They have worked out the genome of the coeocanth. I first learned of this remarkable fish in an article entitled, if memory serves, “A Fish Named JLB Smith” after the man who first described it. Google search for the article was not helpful because there was so much about “A Fish Named Wanda.”
The Coelocanth has lobed rather than rayed fins. It is rare. Evidently the rayed fin is more efficient. But the lobed fin apparently was transitional in the development of tetrapods like us and birds and puppies and snakes.
The fish had long been known in the fossil record but vanished in the Cretaceous era, dinosaur times. You probably would be very surprised to see a dinosaur or any of its contemporaries. That’s not to mean they don’t exist. Crocodiles have been around longer than dinosaurs. Of course you would be more surprised than pleased if a crocodile came for you, but you know they are around somewhere.
Find it they did and it has been called a “living fossil.” That notion has been pooh-poohed but when they looked at the genome (Chris Woolston “Living Fossil” Genome Unlocked NATURE vol. 496 no. 7445 April 18, 2013 page 283) they found that the genes themselves had undergone remarkably little change for a long time.
I had always been rather disappointed at this, almost our best approximation of the doughty, intrepid little ancestor that first ventured ashore. Lung fish I guess are closer. But I thought, “Did it have to be so ugly?” Nay, the picture in the article shows it a magnificent blue to blue green with rakish flecks of pure white. So that’s nice.
The logic I follow when explaining why population sizes are so limited is this: You can’t have evolution without speciation. You need to split off a species for it to be able to evolve independently. So there is a race to speciation, but the down side to speciation is that the maximum long term viable population is about half the number of generations it takes for speciation to occur. Violating that limit ultimately will lead to extinction because of speciation effects. So evolution has fitted us out with a mechanism – a mechanism I am trying better to characterize – that knocks off a population that is in violation and does so long before speciation effects would.
But there was always this whisper in the back of my mind. “That mechanism is not required for the welfare of the individual. If somehow the mechanism were to be lost, survival and reproduction would persist for a long time.” And of course the mechanism could be lost; anything can break. But in order to survive that loss for a very long time, the creature would also have to loose its tendency toward speciation. Turn off speciation and you can turn off the mechanism. But of course then you also turn off evolution.
Evolution, indeed speciation, are not utterly absent in the coelacanth. Indeed there are two known species. But it appears that they have been greatly reduced. So I can think of two possible results. Perhaps some day, long after the mechanism I describe has been nailed down to its DNA fundament, the mechanism will be found to be absent in this fish.
The second possibility is that freed from the mechanism the fish is able to abandon the tight mating strategy the rest of us must abide by. That means when the population biologists look at it they will find its “effective population size” is much greater than that of any other animal of comparable size.
It’s just a thought.
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