sharks have been around longer than trees, perhaps. but longevity is not necessarily a measure of fitness. only now do they finally have mammals to compete with. the way that humans are changing the ocean may act as a catalyst for the mammalian takeover of the ocean, as they are more adapted to adjust to changes in the ocean, but that strikes me as an inevitable process. none of us will live to see it, no doubt, but it will be interesting to see if chemical changes in the water provide for the die-out necessary for mammalian radiation. like an asteroid hitting the ocean, to use an analogy.
i have a lot of problems with the way that biologists "do" evolution. rather, i like the idea of evolution as a function of environmental change. it reduces evolution to a kind of geology. oxygen goes up, the size of insects increases; temperatures change dramatically, and mammals move into opening niches. but, in this context we see something that is certainly an improvement, in any measurable way: the ability to survive changes in temperature seems almost elementary from the perspective of an advanced mammal like humans. if i'm assigning a direction, it's in the direction of robustness - but as a reaction to changes in environment that can be measured using physics.
when you really realize this, it becomes difficult to argue against climate change on the basis of restricting species diversity. if species are unable to withstand changes, other similar species that *are* able to withstand those changes, or thrive in them, will move in. you can view it as catalyzing evolution towards robustness. hey, maybe you actually want to keep an eye on polar bear and wolf hybridization for that reason. but it's bound to create more robust species, and they will diversify again on advantageous terms. not that there aren't better reasons....
how did polar bears happen, anyways? you'd have to think they were probably bears that got chased out of their range, and slowly moved into the north, adapting as they went. they were more or less pinched out of the bear genome and set adrift. an exploratory mission for the genome - possibly beneficial, but ultimately entirely expendable. and, so, anything that returns will be a net gain and contribute to a more robust type of bear. but, if nothing returns at all, there is not a loss because it was essentially expelled dna.
ah, but i'm interpreting evolution as a crossing graph rather than as a tree - i am understanding hybridization as a driver of evolution, through hybrid vigour. and, that's maybe a little cutting edge and hard to follow. it's simply the idea that what we're seeing right now with coywolf hybridization is a good model to use to explain how closely related species combine into a form that eventually assimilates one or both founder species, as a response to changes in environment. that could in theory create an ursid form from grizzly and polar founders that is actually better suited for the new arctic.
www.theweathernetwork.com/news/articles/new-regulations-provides-more-protection-to-endangered-shark-species/35812/