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Mammal evolution, literallyMammal evolution, literallyPosted Nov 20, 2012 21:39 UTC (Tue) by man_ls (subscriber, #15091)In reply to: Experimenting on the BSDs by viro Parent article: Crowding out OpenBSD Good point, and one that I cannot resist. It is hard to compare between different living groups: birds may have a slight advantage in eye resolution, but hardly in nocturnal sensitivity or in fact in many other senses: hearing (bats, dolphins), smell (pigs, dogs) or taste are arguably topped by mammal representatives, owls notwithstanding. In fact adaptation to different ecosystems is the only measure of success that we may objectively use. We might focus on how our group of previously dwarvish creatures (less than a metre long) have invaded almost all ecosystems, often becoming their apex predators. Birds have not colonized the seas, for example, other than flying above them; and yet they have a whole continent (Antarctica) to them. If we follow this line of reasoning, we might argue that bacteria are the living champions and that we should devolve to single cell organisms, since we have 10 times more bacterial cells in our bodies than human cells... But the particular thing I had in mind was that crazy habit of laying eggs around and then abandoning small birds to their luck after at best a few weeks. This is way better than fish just lying eggs around, but much worse than our viviparous system. By "evolving into mammals" I was specifically thinking about breast-feeding their offspring, which allows us mammals to create affective bonds and teach every new generation the old tricks. That is the indubitable advantage of primates which humans have taken to an extreme, by living several decades with their parents. So our friendly penguin-like operative system should evolve towards the breast-feeding dolphin and not backwards to the offspring-eating shark, even if some of them are viviparous.
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Mammal evolution, literally Posted Nov 22, 2012 7:25 UTC (Thu) by viro (subscriber, #7872) [Link]
"Slight"? A bleeding pigeon has resolution more or less on par with what horses have; compare the eye sizes... For a typical mammal 5 stripes per degree is on the edge of being indistinguishable from grey field. Cats are somewhere about 6--8. Camels are circa 10. Horses - 15 or so. And those are the best outside of anthropoidea. We rate at about 50--75, so do falcons. Large eagles are at about 140 (bigger eye => bigger retina => more sensors in the cell array the image is projected upon => higher resolution). Pigeons, IIRC, are somewhere about 15...
As for vivipary vs. ovipary... Archosaurs use the eggshell as calcium store for embryo, so they are pretty much locked into using hard-shelled eggs. Which has very little to do with the amount of time newborns spend in contact with parents; precocious mammalian species can have the contact ending very fast and "few weeks" is nowhere near the longest you can get with birds.
The only measure of clade being successful is its survival; scala naturae is an artifact of the way we use mnemonics to turn messy and complicated history into something that can be easily remembered, as long as you don't look into details...
Mammal evolution, literally Posted Nov 22, 2012 9:56 UTC (Thu) by man_ls (subscriber, #15091) [Link] The figures you quote are fascinating, thanks.The resolution each species you have mentioned has is -- what it needs to survive. Or more specifically: the lowest resolution it can get away with. Birds of prey need to locate their victims from a long distance; primates need accuracy to locate tree branches when they jump. Note that horses have better eye resolution than humans overall, but do not have a central fovea with increased accuracy. The fact is that longer development periods are present in mammals than in oviparous animals. Even marsupials have to support their offspring for a certain time before they are ready -- not so with the more primitive monotremes. I think that breasts and milk are great advancements that have allowed mammals to thrive in many environments and in harsh conditions -- for example allowing the mother to feed their offspring even when the environment is bare. I am not trying to establish a single scale from bacteria to humans; each species is almost by definition well adapted to its environment, or it will perish. Adaptations are always amazing: albatross have a gland to secrete excess salt so they can drink sea water, condors can reportedly fly up to 10 km high, penguins thrive in the Antarctic. But there is a measurable degree of change, or divergence from the original form. There are many species which have survived unchanged during hundreds of millions of years. Mammals, primates and humans have evolved a lot from the time of dinosaurs, changing not only morphologically but also biochemically. For a simple example compare elephant trunks, dolphin tails, bat wings and human hands. While most birds are still very similar to their dinosaur ancestors in their basic shape.
Mammal evolution, literally Posted Nov 22, 2012 15:40 UTC (Thu) by raven667 (subscriber, #5198) [Link]
> There are many species which have survived unchanged during hundreds of millions of years.
Unlike the pop aphorism "Survival of the Fittest" the real world is more like survival of the fit-enough.
Mammal evolution, literally Posted Nov 23, 2012 11:58 UTC (Fri) by dgm (subscriber, #49227) [Link] Indeed. It should be "Survival of the Fittests". Sexual reproduction makes survival of a single individual... a bit futile.
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