A species of Italian wall lizard was found on an Adriatic island called Pod Kopiste. Some of these lizards were transferred to another island called Pod Mrcaru, where they changed over a period of 36 years. The changes entailed the size of the head and jaws, owing to a change in diet from insects to plants, and most interesting, the development what is termed a new feature, cecal valves in the intestine, attributed to the need to aid digestion by creating "fermentation chambers in the gut", ostensibly needed for plant digestion.
But also attributed to the development of the cecal valves are the presence of nematodes in the vicinity:
"Cecal valve evolution probably went hand-in-hand with a novel association between the lizards on Pod Mrcaru and microorganisms called nematodes that break down cellulose, which were found in their hindguts.”Come again? The presence of nematodes breaking down the cellulose should work against the need for cecal valves, not for for it. This unproven jump to conclusion is indicative of... well, jumping to conclusion.
The Pod Mrcaru lizards were genetically compared to the original population at Pod Kopiste, and were found to be "genetically identical to the source population on Pod Kopiste". Identical? Really? As in totally identical?
There is something wrong with this picture. First, the cecal valves appeared as required by dietary needs; this is not a true evolutionary idea. Evolution requires undirected, stochastic modifications. Unless, of course, the environmental stress causes an existing gene to be selected that previously was not selected. If this gene was there before, why was it? Moreover, how is "genetic identity" arrived at when there are obvious differences in the populations, unless the genes preexisted or the testing is not a true test of the situation? So why is this called "evolution" if all the elements were in place to start with? How do they know that the Pod Kopiste population did not just hide the cecal valves due to disuse? How do they know that the situation is not a negative evolution to a prior state?
They haven't even thought of these questions much less addressed them, because they jumped straight to evolution.
The mystery of what biologists like to call speciation via selection (of mutations I still insist) is not found in the expression of existing genes; it is found in the existence of genes at all: why should they even be there? Plus, if they are not used but are just waiting around for a good reason to be expressed, that is more than rational probabilities can handle.
Cecal valves do not prove a) to be a new structure; b) to be rapid evolution; c) to be anything more than microevolution just as are the head and jaw size. This is the same as the oscillating beak size of the Darwin Finches on the Galapagos. It is not likely evolution except in the stasis mode, oscillating within the genome.
1 comment:
From my understanding, the cecal valves are needed for fermenting, so they do correlate to the presence of the nematodes. But this should come as no surprise to anyone who has studied symbiosis and symbiogenesis. It is quite possible that gene expression was altered by the presence of nematodes in order to express the cecal valves. It's the best hypothesis that I have heard.
But the thing is, this in no way demonstrates evolution in the sense I think most people want to assume. It's really just a symbiotic relationship that formed from the dietary change and perhaps had minor genetic and epigenetic effects which have been inherited by the rest of the population.
It could be adaptation, there could be some sort of genetic modification and it could very well have non-random origins (a few switches have been turned back on due to physiological feed back from the activity of the nematodes). That's my take on it.
Why people think this has something to do with reptiles turning into mammals is beyond me.
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