Advanced Mice & Backward Humans [DNA studies]
“It is not quite Jurassic Park, but it could prove just as interesting. This week, researchers announced they have reconstructed a million-letter-long DNA sequence from a mammal that lived 75 million years ago and was the ancestor to almost all the mammals now roaming the Earth, including people. The ultimate aim is to reconstruct the entire genome of this long-extinct species.… They worked back from a stretch of DNA that has been extensively mapped in 19 mammal species, as it includes the gene CFTR, which is implicated in cystic fibrosis in people… Delving into our genetic past also promises the tangible benefit of new perspectives on genetic diseases. At least one of the genetic variants that cause cystic fibrosis in humans turns out to be the normal form of the gene in our 75-million-year-old ancestor, which suggests the problem is not the gene itself but the context in which it functions today.” (New Scientist, 04 December 2004)
No one knows what the ancestor looked like, but the general view is that it was a small voracious insect-eater, not unlike a modern shrew, and lived obscurely in a world where dinosaurs dominated. New Scientist says that actual shrews are members of an older offshoot, one which also includes elephants and anteaters. Other sources disagree and class the true shrews as insectivores, related to hedgehogs—only the similar-looking ‘elephant-shrews’ are genuine elephant relatives. Only when they do more DNA sequences will anyone be sure.
What I found much more interesting is the degree of change to the DNA since the ancient ancestor. Humans are the final product of evolution, so we must have changed the most, right? No, not right at all. The small chunk of genome that’s been sequenced shows 8 to 9 per cent changes for monkeys, apes and humans, with humans getting the lowest score. Cats, dogs and horses are in a range of 11 to 12 per cent, with 13.5 for dogs. The mouse comes top, with an astonishing 17.5% change, more than double the human score.
There was probably more evolutionary pressure on mice, typical small mammals, than there was on primates living a specialist life up trees. To make an analogy from the commercial world, if you are a shop that sell groceries, you’ll face a lot of rivals and must be very competitive. If you sell pet fish and aquarium equipment, you may be the only outlet for miles and have an easier life.
That’s also why the results of Natural Selection are mostly tedious and repetitive. Naturalists show you the high spots; there is a lot more dross. It looks like pure chance that one line chanced to develop from primate to ape to semi-human to modern human. Nature rambles and the moon don’t care.
I’ll also risk a prediction. If someone manages to do the same trick for animals in general or for life in general, I’m sure they will find the same effect, more actual change in the DNA of creatures we view as primitive. They might even find that plants are the most evolved creatures of all, in terms of DNA. Land-plants emerged after animals—we find animals as complex as most modern creatures in the Cambrian oceans, but the first plants with leaves and roots come much later. The first flowering plants developed in the Cretaceous, the final Age of Dinosaurs, and they have changed a lot since then.
(From Newsnotes, January 2005.)