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Re: Ask me about evolution

Postby cmsellers » Sun Nov 13, 2016 3:35 am

Anglerphobe wrote:Okay, a serious one now. Why does South America have an abundance of monkeys while North America is almost entirely monkey-free? I really can't wrap my head around it. The continents of Africa and South America separated far too long ago for them to simply be the two divergent halves of an existing population, and I can conceive of no feasible way that a monkey could reach the new world from the old.

The current thinking is that monkeys reached South America from Africa via rafting when the continents were still relatively close together. Old World monkeys form a monophyletic clade and are more closely related to apes than to New World monkeys, meaning you're more closely related to a baboon than a baboon is to a capuchin.

As for why South America has monkeys but North America doesn't, that relates to the broader question of why North American animals were much more successful at colonizing South America than South American animals were at colonizing North America during the Great American Interchange (the two most notable examples of the latter are the opossum and the armadillo, both of which are remarkably versatile creatures). There are usually two main reasons given for this:

  1. Most of South America is tropical but only a small portion of North America is. North American animals were able to cover most of South America without adapting to temperate climates, while South American animals had access to tropical climates only as far as southern Mexico.
  2. North American animals had to compete with the best of Eurasia and Africa (well, the best temperate-adapted animals) via the Bering Straight land bridge, while South America had been an island, meaning South American animals only had to compete with animals that arrived via rafting until a land bridge with North America was formed.
The northern limit of New World Monkeys is roughly the limit of the tropics. As far as I know, other than humans (who invaded temperate climates multiple times in our evolution) there is only one group of primates which has successfully invaded the temperate zones: Japanese macaques, which have invaded the southern fringes of the temperate zone in Japan. There seems to be something about primates which is averse to cold, and I suspect that it isn't due to any particular adaptation that humans can survive it (humans lived naked in Tierra del Fuego, suggesting it's not just clothes), but rather our size. On the other hand Old World Monkeys often live in subtropical regions (rhesus macaques have been introduced to northern Florida, for example), so I suspect that it's probably the specialized diets of the monkeys that happened to make it into Mexico which limited their expansion further north. They're all members of the spider/howler monkey family and all have diets limited to fruit and/or certain kinds of leaves.

Interestingly, one exception to the pattern of North American species being more successful is found in the Caribbean, which is of course a collection of Islands making it necessary for species to arrive via rafting. Prevailing winds favor South American fauna (especially birds) and some South American species have been introduced to the tip of Florida (also tropical) without having to go the long away around. I wasn't aware of any native monkey species native to the Caribbean, so I looked it up, and monkeys made it as far as Cuba, but then were mostly killed off by the Indians and finished off by the Spanish.
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Re: Ask me about evolution

Postby DoglovingJim » Sun Dec 04, 2016 3:49 pm

cmsellers wrote:There are a couple people on TCS whom I think might be creationists, but we're all friends here, right?

And which of us do you presume are creationists?

cmsellers wrote:
random_nerd wrote:Sleep. Is anyone any closer to figuring out why damn near every multicelluar organism needs to become a sitting duck for at least a few hours every so often?

Not as far as I know. One argument I've heard is that you can be adapted for the night or day but not really both so hiding during the wrong time period makes sense. But that doesn't explain why sharks need to sleep.

I remembering reading about two theories for the purpose of sleep in some book about scientific studies once, but I forgot them. Ah right, the restoration theory and survival theory (perhaps cmsellers knows about it, or I can look for that book and give you a proper explanation of it). But like all theories there are also faults in them, such as facts which conflict. And with most studies there is usually some sort of extraneous variable so nothings been proven.
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Re: Ask me about evolution

Postby cmsellers » Mon Dec 05, 2016 3:49 am

DoglovingJim wrote:And which of us do you presume are creationists?

I asked both of them, and it turns out that neither is a creationist, but one was raised creationist and both have a lot of creationist family, so they kind of found my posts on evolution flippant and dismissive.
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Re: Ask me about evolution

Postby Anglerphobe » Wed Dec 14, 2016 1:28 am

Why do humans lack a penis bone? It seems odd that we, uniquely (? as far as I know) among primates and unusually among mammals should have boneless genitals.
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Re: Ask me about evolution

Postby cmsellers » Wed Dec 14, 2016 2:12 am

Anglerphobe wrote:Why do humans lack a penis bone? It seems odd that we, uniquely (? as far as I know) among primates and unusually among mammals should have boneless genitals.

Because God used it to make Eve.

But seriously, I didn't know the answer. Fortunately, Wikipedia has at least three answers. The best one seems to be that it's so that we can come early and often. Richard Dawkins says it's because women like a man who can keep it up unaided, and the ever popular "it's because humans are overgrown baby chimps" explanation is also raised. One explanation Wikipedia implies but doesn't mention: it's not clear that the penis bone really has much function in other great apes; it's possible that we lost it because we don't need it.

And if you're too lazy to follow a link...
Wikipedia wrote:Unlike other primates, humans lack an os penis or os clitoris; however, this bone is present but is much reduced among the great apes: in many ape species it is a relatively insignificant 10–20 mm structure. There are reported cases of human penis ossification following trauma,[22] and one reported case of a congenital os penis surgically removed from a 5-year-old boy, who also had other developmental abnormalities, including a cleft scrotum.[23] Clellan S. Ford and Frank A. Beach in Patterns of Sexual Behavior (1953), p. 30 say "Both gorillas and chimpanzees possess a penile bone. In the latter species the os penis is located in the lower part of the organ and measures approximately three-quarters of an inch in length."[1] In humans, the rigidity of the erection is provided entirely through blood pressure in the corpora cavernosa.

It has been speculated that the loss of the bone in humans, when it is present in our nearest related species the chimpanzee, is because humans "evolved a mating system in which the male tended to accompany a particular female all the time to try to ensure paternity of her children"[10] which allows for frequent matings of short duration. Observation suggests that primates with a baculum only infrequently encounter females, but engage in longer periods of copulation that the baculum makes possible, thereby maximizing their chances of fathering the female's offspring. Human females exhibit concealed ovulation also known as 'hidden estrus', meaning it is almost impossible to tell when the female is fertile, so frequent matings would be necessary to ensure paternity.[10]

The evolutionary biologist[24] Richard Dawkins speculated in 1989 that the loss of the bone in humans, when it is present in our nearest related species the chimpanzee, is a result of sexual selection by females looking for honest signals of good health in prospective mates. The reliance of the human penis solely on hydraulic means to achieve a rigid state makes it particularly vulnerable to blood pressure variation. Poor erectile function portrays not only physical states such as diabetes and neurological disorders but mental states such as stress and depression.[25]

A third view is that its loss in humans was a side-effect of neoteny during human evolution; it is noted that late-stage fetal chimpanzees lack a baculum.[26]
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Re: Ask me about evolution

Postby Tesseracts » Sun Dec 25, 2016 6:29 am

I don't know if this really qualifies as a question about evolution, it's more about biology in general. I'm wondering why cold blooded creatures have less blood. I saw a video of a guy butchering an alligator for meat, and there was hardly any blood at all.
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Re: Ask me about evolution

Postby cmsellers » Sun Jan 01, 2017 6:59 pm

Your question pre-supposes a fact I don't know to be true.

Cold-blooded animals have a much lower resting metabolism than warm-blooded animals, meaning their blood circulates (and would likely also drain) much more slowly.
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Re: Ask me about evolution

Postby DoglovingJim » Thu Jan 05, 2017 5:38 am

Why do zombies eat brains? And why does one must destroy their brain to kill them?



Wait... What if they eat the brain because they think we are the zombies, and they are trying to kill us properly?
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Re: Ask me about evolution

Postby cmsellers » Thu Jan 05, 2017 5:57 am

The zombies who tried to eat other body parts first were easier to kill, so only the brain-eating zombies survived. (Well, the genital-eating zombies also survived, but for some reason only the porn people make movies about those guys.)

And zombies the fact that zombies still have rudimentary sensory perception and motor control suggests that they maintain partial brain function. This means that like any higher organism, you can kill them by severing the rest of the nervous system from its control center.
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Re: Ask me about evolution

Postby CarrieVS » Thu Jan 05, 2017 9:53 am

How big would pterosaurs have got if the asteroid hadn't hit? How big could something get and still be able to fly?


They could have evolved to breathe fire, right? Right?
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Re: Ask me about evolution

Postby cmsellers » Fri Jan 06, 2017 1:44 am

What? Are the 30+ foot wingspans some pterosaurs actually had insufficiently impressive for you, cat?

We still don't really understand how pterosaur flight worked, or at least scientists were still trying to figure out the mechanics of it last time I checked. We do know that birds should not be able to get nearly as large as Quetzalcoatlus and still fly (the largest-known flying bird didn't even reach twenty feet tip-to-tip), in fact it's possible that the largest known pterosaurs had wingspans twice that of the largest known flying bird.

So until we figure out how pterosaur flight worked, I suppose the sky's the limit for wingspan size.

Edit: as for evolving to breathe fire, probably not. Natural selection has produced a whole lot of weirder adaptations, but I know of none like fire breather and I think I know the reason why: I imagine fire-breathing has never evolved because it would involve surrendering a lot of high-quality fuel for a rather inefficient attack/defense mechanism. Venom can make you feel like you're on fire for a fraction of the caloric costs.
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Re: Ask me about evolution

Postby CarrieVS » Fri Jan 06, 2017 10:58 am

Oh don't worry, I'm absolutely staggered and astonished by Quetzalcoatlus.

I watched Flying Monsters with David Attenborough nearly a week ago and he met a guy who showed him a wrist bone from it. It was around the same size as an elephant's long bones - maybe shorter, but I think bulkier. Its wrist. And it flew.

Standing on all fours - and it was quite comfortable standing and walking - it was the same height as a giraffe, and not dissimilarly proportioned, save that a giraffe doesn't have a beak as long as a person.

That's why I'm wondering. Fully appreciating the size of it has turned my view of flying creatures on its head and I'm still in a state of amazement a week later. Things are evidently possible that are scarcely believable, and I have yet to reestablish a reference frame for what's reasonable.


And I want dragons to be possible. Real proper dragons. How about spitting some kind of corrosive venom? That's almost the same thing as fire. What about spitting a venom that's a strong enough oxidising agent to set things on fire when it hits them?
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Re: Ask me about evolution

Postby cmsellers » Fri Jan 06, 2017 5:57 pm

CarrieVS wrote:And I want dragons to be possible. Real proper dragons. How about spitting some kind of corrosive venom? That's almost the same thing as fire. What about spitting a venom that's a strong enough oxidising agent to set things on fire when it hits them?

That sounds entirely plausible to me, but keep in mind: I'm not a real biologist; I just play one on the internets. Also, I think you'd need a biochemist to figure out the details of your proposal.
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Re: Ask me about evolution

Postby Kivutar » Fri Jan 06, 2017 11:13 pm

CarrieVS wrote:How about spitting some kind of corrosive venom? That's almost the same thing as fire. What about spitting a venom that's a strong enough oxidising agent to set things on fire when it hits them?


It's hard to see how they would store those chemicals internally. Some insects like bombardier beetles do similar things, but they actually mix the ingredients just prior to expelling the liquid. Also, insects have their hard crunchy bits, which pterosaurs wouldn't.
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Re: Ask me about evolution

Postby CarrieVS » Sat Jan 07, 2017 12:39 am

:'(
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