Why haven't any primates developed flight? This seems to me to be an obvious advantage.
It requires enormous sacrifices for weight reduction. Birds have hollow bones, which break easily. They have air sacs that make use of the outside surface of their lungs, a favorite gathering spot for mites. Their immune systems are so stripped-down that avian medicine has not made great strides in conquering or even identifying their diseases. It would take a very long time for a mammal to evolve these systems. This is why flight is limited to the tiniest of mammals. (Bats fly, but "flying squirrels" can only glide short distances in a generally downward direction.)
An entire order of birds, the ratites, have evolved in exactly the opposite direction, and they have been fabulously successful. The ostriches, cassowaries, etc., gave up flight, grew to gigantic sizes, and use their long legs for running away from predators or kicking the crap out of the ones they can't outrun.
The psittacines evolved lethal hooked bills for fighting, prehensile claws for climbing, flock-social behavior for defense and primate-level intelligence for strategy. Many parrot species fly only incidentally and spend more time clambering. In aviculture, African Greys are noted for "flying like rocks."
Flying is perhaps not such an ideal ability.
Why haven't octopedal invertebrates made the transition to land?
The migration from water to land is similar to that from land to air. It requires losing a lot of weight and evolving whole new ways of getting about. For starters, if you want to be larger than a worm, without the buoyancy of water to support your floppy body you need either an exoskeleton, which allows you to reach the size of the largest cockroaches--about a foot long--or an endoskeleton like ours. Endoskeletons are not easy to evolve.
The cetaceans have taken a route similar to the ratites: lost their legs, returned to the sea and reached enormous sizes, becoming the apex predators in their ecosystems. In fact virtually every warm-blooded air-breathing animal that tries its luck in the water finds an easy life there. Penguins, ducks, seals, otters, polar bears... DNA analysis recently discovered that the cetaceans are merely the descendants of primitive hippopotamuses who swam all the way down the river to the sea, liked what they found, and kept going.
With 8 appendages, it seems like they would have an automatic advantage.
Yet myriapods (centipedes and millipedes) and arachnids (spiders) are almost all tiny and are virtually footnotes in the history of land animals. Even the insects with their six legs, while highly successful, are small. There's a reason engineers have standardized on four legs or four wheels to support their artifacts. It's the best compromise between adequate support and leaving enough mass for your original purpose.
I know these seem like silly questions, but I have always wondered this stuff. Why did we develop a liver, for example?
Livers are really important, they filter out toxins. As far as I know all vertebrates have them. You probably take fish liver oil or something similar to add antioxidants to your diet.
OR more to the point, the appendix. Has it ever had a use?
That question has not been definitively answered yet but it's getting a lot of attention. The most plausible theory is that it's just the vestige of a much longer intestine. We're the only primates who evolved into carnivores, so we no longer require miles of bacteria-rich intestines to digest cellulose. The other hominoids ("great apes") have appendices too even though their intestines are longer than ours. They still eat leaves, but insects and even larger animals are an important source of nutrition.
What is the advantage of holding the egg on the inside, rather than laying it and having it fertilized?
How about the fact that you can get by with laying a small number of eggs instead of dozens or hundreds which will provide food for predators?
Evolution is a myth. . . .
Huh? Please explain. Here in the Academy we call it a canonical theory.
