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1

As I have already mentioned in my other post, the most important role of urea synthesis by humans is blood pH regulation and urine concentration, so it is not just about excreting a waste product... I don't think human body is very special in this case, so I think most of the urea excreting mammals use urea for the same purposes. The urea is created from ...


1

Dehorning of rhinos has been tried with limited success. Poachers have killed dehorned rhinos anyway, either out of spite or to avoid tracking worthless prey in the future. There is the problem of anesthesia (always a risk) and the fact that rhino horns are usually not destroyed but saved in the event of decriminalization. But at least horn grows back. ...


1

If rates of meiotic recombination DIDN'T vary across species - THIS would require an explanation! After all, evolution creates diversity, not homogeneity. I can only wonder that more recombination would allow for a faster diversification. The more DNA you shuffle, the more distinct each individual offspring may be (though I'm not 100% sure). The ...


2

Here is a more morphologic, less genetic answer: According to this article, the 2 sets of paired appandages (shoulder and pelvic) was set in stone when agnathans transitioned into gnathostomes (ie. when the first vertebrate organisms began to evolve jaws, an anatomic change that allows for classification of different stages of history found in the fossil ...


6

The answer by Remi.B is excellent, I'll just attempt an explanation by way of gene networks: In genetics we see new genes "linking" to the older genome by regulation pathways and by being "fit" only in the context of the existing genome. This has the effect of making the older genes indispensable. Change them and you rupture the whole mesh. If you want to ...


7

I think I might interpret your question as asking, not just why don't mammals have more than four limbs, but why arthropods have more variety. Insects have six, but others have eight, ten, or more. Partly there are just many more species of arthropods. 80% of animal species are some sort of arthropod, and some lineages of arthropods are distantly related ...


32

Number of legs in terrestrial vertebrates Not only mammals have four legs but actually all terrestrial vertebrates (which include mammals) have four legs. There are slight exceptions though of lineages that have lost their legs. Typically snakes have no legs anymore. Apesteguia and Zaher (2006) discuss the evolution of snakes legs reduction and report a ...



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