I think that once you are ‘strong’ enough, there is very little selection pressure for ‘smarts’, and vice versa. A tiger is a sufficiently lethal killing machine that being a couple of percent ‘smarter’’ does not significantly affect the chances of survival and reproduction. It is however, sufficiently
‘smarter’ than most of it’s prey to get by.
Humans have the flip situation - our brains/tools compensate for a lot of our physical shortcomings, such as they are. Although I am not sure I agree with all of the list of weaknesses the OP has. Sunburn becomes less of an issue if you either cover up or have more continuous exposure. We operate in teams, a not uncommon strategy for dealing with things your own size or bigger.
Ok, if we did in fact come from quick enduring sneaky alert little guys, what happened? We lost much of that. Without work, we are none of those things. Why would they go away? Wouldn’t being alert AND smart be better than just alert or just smart?
I guess what we need to know then is if we have, in fact, evolved into a more ‘nature resistant’ organism. If so, did our ancestors have neither our current mastery of environment, nor the physical advantages of more robust species ?
My impression though, is that according to the prevalent family tree, we’ve given up some
robustness in our last few leaps - do you know of any good info contradicting this ?
Right now I’m starting to like jsleeks notion
I guess what I’m wondering about is a mechanism within the framework of natural selection which would explain eg our dvelopment of fragile skin - have we been using clothing long enough for natural selection to take it into account to such an extent that the advantages of a skin which can wear different clothing in different climates have completely eradicated the leathery/hairy skin genes ?
I’m imagining a bunch of cavewomen refusing sex to leathery/hairy cavemen…
Like MMI said, we operate in teams. Some animals, like humans, did not only evolve as individuals, they also evolved as societies and the group was integral to an individual’s survival. Lucy by herself was leopard meat. (Think of leopards more as our primary predator, not lions. A human is poor pickings for a pride of lions.) Lucy with a half dozen other mean li’l bastiches with sticks and shoulder girdles designed for swinging them is bad news for the neighborhood’s leopards.
As for “fragile skin”, our recent ancestors from Africa most likely had dark skin (like most current natives of that continent) that was not “fragile” when exposed to the sun. Lighter skin as a northern climate adaptation to allow more synthesis of vitamin D.
The loss of hair could have had many advantages. Several have been speculated: better cooling mechanism, better way to rid the body of lice when sleeping in the same place repeatedly, or just making the body more “sexy”.
Also, don’t confuse the obvious weakness of modern couch potatoes with the natural strength humans have when they have to work hard, physcially, every day just to survive.
I cannot provide a link to any cites on this at present, as am busy at work, but I did want to point out a possible misconception you have about our own evolution.
According to the current model, the majority of our evolution took place on the plains, savannahs, sparse forest, and deserts of africa. In nearly every environment in our development phase, food was extremely sparse and often difficult to get consistently.
To develop an organ as large and energy hungry as the brain requires a LOT of calories, and more importantly protein. Once our environment began selecting for larger-brained individuals, it became increasingly more difficult to also include lots of bulk muscle, dense bones, or thick fingernails/claws/fangs. Because those things also require lots of calories and protein.
If however, homo sapiens, had done more of their evolving in an environment that selected for both large brains AND physical prowess, and was capable of providing the requirements for both (such as the ice age world of neanderthals), individuals would be capable of becoming both extremely physically adept and mentally adept.
It’s very hard to provide enough energy for “a brain the size of a planet” ™ when you are constantly dealing with droughts, competition from other predators, and other tribes. If you were going to try the same thing and also provide enough to develop bigger stronger faster bodies on top of it, you aren’t likely going to survive as a species.
I think your basic premise is flawed. Human bodies can sustain an incredible amount of damage and still function. We can lose limbs and appendages and survive. We can lose eyes and teeth. We can drill holes in our freakin’ skulls and survive, for cryin’ out loud! Evidence is that early humans were doing just that, well before anything resembling modern surgery came into being.
We may not be able to take on a Ferocious Tiger[sup]tm[/sup] mano-a-gato, but then we rarely ever had to. We evolved as a social species, and have remained so. Predators in general attack loners, not groups. Thus, we had no need of super strength and claws and fangs (translation: pressures which would have selected for such traits were absent). We had other members of our species, and big brains. With those two traits combined, we have become one of the most dominant species on the planet (barring critters like batceria and cockroaches).
Yes, that is a prominent theory, but one also needs to consider Neanderthals, who shared the bulk of their evolutionary past with us, had brains as big as ours, but were much more muscular.
Another thing to consider is that we are better physically adapted in many ways than our ape cousins. For example, chimps often throw rocks or long sticks at predators to scare them. If you’ve ever seen them do this, they’re not very good. Kind of a wild, underhand toss that’s not good at actually hitting a target. Contrast that with even an untutored human throwing a spear or a baseball. We’re really good. Also, our thumbs are much bigger and more manuverable than a chimp’s. Much better adapted to both fine manipulation of objects and a powerful grip on something like a spear. Chimp thumbs are tiny, much weaker, and not as easily used with all the other fingers.
Once more with feeling: qualitative valorations of “would be better” have jacksquat to do with it. Results-on-the-ground do, and obviously H. sapiens must have been doing something right…
You have answered yourself: “without work we are none of these things”. Neither would the hominids, had they access to cable TV Just maintaining life itself as a hunter-gatherer provides a strenuous physical and mental workout (and an all-organic diet). And who says the “alert” part went away? There’s people around today as alert and sneaky as ever. I’ll go further and say that in our very day and age, they are still coming out on top (think Bill Gates). It’s just that our environment has been changed so that these traits are manifested differently and a lot of us never need to work on them.
As to “why the (earlier traits) would go away”? Like I said, I’m not sure they’ve really “gone away”, but in any case if the non-use of a trait is (a) nonlethal and (b) causes no adverse reproductive effect, then any degeneracy of that trait that may happen through gradual mutation or dilution of the gene pool will not be checked. We can no longer detect who has been in our territory by smell? Big deal, we don’t need to.
In any case, a lot of genetic traits are predispositions, whose manifestation is then based on environmental stimuli during the developmental years. If you’re raised lying on the couch in front of the TV munching cheetos you will not become a very quick or alert adult even if your dad was Sugar Ray Leonard.
No. What apparently happened is that we developed in an area where hairiness is not needed to keep us warm and can even be a disadvantage by slowing heat loss. An ancestor had a mutation for less hairiness and it proved to be a very successful mutation in that place and his descendents with that mutation became the majority of humans. As humans spread out from East Africa they entered climates where hairiness became less of a disadvantage and even an advantage so it stopped being selected against in those places, giving us Europeans who have more body hair than their African cousins, for instance. However, you can’t sit on a glacier for a thousand generations hoping that your descendents will be hairy enough to survive so some smart human wrapped himself in an animal skin or bark or something. His friends were no dummies so when they saw how toasty warm Org was they wrapped themselves up, too. Voila! It stops being a disadvantage to not be hairy.
Patterns of hairiness are interesting, though. Let’s look at the head. Your brain puts out a lot of heat and needs to be kept cool in a hot climate and insulated in a cold climate. But doesn’t hair insulate the head, potentially causing dangerous overheating in the tropics? Go out in the hot sun. After a time touch the hair on the top of your head or your hat if you are bald. Pretty hot, huh? Bet you’re real glad your scalp isn’t that hot. So your hair apparently also reflects heat and insulates your head from some of the heat in the environment.
Okay, how about body hair? The piddling amount even the hairiest normal humans have couldn’t help keep us warm, could it?
Inadvertent experiment: While lighting my furnace I caused a fireball to singe off all of the hair on my right arm. As I often wear short-sleeve shirts and no jacket, even down to about freezing, I was able to feel the difference. You hear about the wind chill during the winter. Understand that the wind chill factor is an attempt to quantify the perceived temperature and that wind will strip the layer of warm air we keep around us. This layer is apparently held in place by that piddling bit of hair because there was a significant perceived temperature difference between my two arms.
Lunch is almost over so I can’t look up the study that suggested that.
Just a quick note. The phrase ‘mano y mano’ means ‘hand and hand’ not ‘man to man’ and refers to weaponless fighting. A more correct phraseology (made up word) of your statemt would be ‘mano y garra’. It’s not important mind you, just a misconception that happens to come up every now and then in fillipino martial arts class.
According to the current model, and please correct me if I am wrong, the Neanderthals branched off from our own tree at the homo erectus phase. Erectus at the time (something like a 1/2 million years ago IIRC) moved out of africa and into asia and europe. For some reason they died off in asia shortly thereafter. The ones in africa evolved into hiedlebergensus (sp? never seen it spelled) and eventually cro magnun, while the ones in europe evolved into neanderthals.
The climates of the two regions are completely different and would favor very different animal types.
In africa, meat would have been fairly rare, hominids would have survived as scavengers, and possibly a weekly large animal kill. Much of their diet would consist of fruits, wild grains/plants, and tubers. The environment would have favored taller, thinner individuals, with darker skin, less hair, and larger pores. For some unknown reason (to me) the hominids of this region also were more intiment and creative with their tools, and were more adept at using them. This kind of environment would have favored large brains, nearly to the exclusion of all else. Any extra energy would have been spent on improving endurance, and increasing the efficiency of the body.
In Ice-Age europe, the world was very different. While neanderthals were probably capable of surviving of the same diet that other hominids were, plant life would have been sparse, and much of it (grasses and evergreen trees) would have been completely inedible and fruitless. Fruit that was available, would have been available for much less of the year than in tropical and sub-tropical climes. Most of their diet would have likely been from meat, and based nearly entirely on small animal kills and large animal scavenging. The heavy forests of the region would have made the endurance hunting methods of the deserts and plains in africa much harder (they were still used, but likely only on extremely large fauna, i.e. the mammoth), so they would have to be on average, faster and more agile to catch the smaller rabbits and similar game that would have been their staples. They still needed their large brains for tool making, socializing, and memory function, but they would also need stronger bodies to meet the more physically demanding environment. Add to that the fact that cold environments generally favor stockier individuals, with thicker hair and lighter skins, and the more dangerous hunting methods employed by neanderthals would favor harder to injure individuals more capable of surviving damage and you can easily see the origins of differences inherent in the two races.
If we didn’t have an instinct to protect our physically weak, we’d never have survived.
Many animals give birth to young that are up acting like miniature version of their parents within hours, if not minutes or even sooner. A colt stands up seconds after emerging from the mother horse, for example. Not us.
To use our cool hands, we had to become bipedal. That meant a fetus does not hang down from a quadrupedal mother, and the pelvis had to change to accomodate walking, creating a smaller gap.
All this said we had to have a shorter gestation period in order to give birth at all, and so we come out basically helpless. We therefore evolved an instinct to assist the helpless, otherwise we wouldn’t go past one generation.
We also need to come out before our brains grow too large to let our heads out of the womb. Gotta have something to control those hands, ya know.
We evolved as the most tool-using of animals, whatever shortcomings we must put up with as a result, and it has obviously been more than a fair trade-off.
You got it mostly right.H. erectus left Africa as early as 2M years ago (1.8M yr old fossils found in the Caucus country of Georgia), and survived in Asia until as recently as 50k years ago. H. heidelbergensis was first discovered in Europe (Heidelberg Man, get it?), but is used for later erectus in both Africa and Europe. It is thought that modern humans and Neanderthals last shared a common ancestor about 500K yrs ago.
As to the question of body hair and burn-prone skin:
Our earliest ancestors were dark-skinned africans, living in a warm climate. They evolved in such a way as to remove heat from the body, with hairless skin that sweats. Why this is, when so many other animals of the region have lots of hair is still not completely known, but that’s what obviously happened, because there the hairless native Africans are.
When humans moved northward, where there is less sun, the skin lightened to get enough sunlight to create Vitamin D and avoid rickets, but our tool-use got us around having to evolve more body hair.
If you take your white-ass skin to a more equatorial location and burn it, that’s your problem. Go back North.
We can’t AFFORD to be tougher. Evolution is all about trade-offs. Yes, there are creatures as big as elephants … but how many, exactly? Aren’t they near extinction? It’s not easy to support that much meat.
Ask the thriving field mouse–or cockroach–why it doesn’t weigh a few hundred pounds. Answer: it doesn’t need to. It gets along just fine at its size.
A more likely explanation is that hairlessness evolved as a side-effect of our (aforementioned) neotenous nature. That is, there was no gene for hairlessness as such that evolved and was selected for (or that a gene for “hairiness” was subsequently lost by being selected against), but we remain hairless because we retain the juvenile trait of relative hairlessness. See this earlier GQ thread for more detail.
Hairiness here, of course, refers more to the thickness and length of the follicles, not the number of follicles per square centimeter, which IIRC is about the same for all apes. Let’s call it the “visible hairiness.”
In your link John Mace said
I’m surprised nobody mentioned to him such savannah dwellers as the aardvark, elephant, and rhinocerous.
What is the advantage, if any, to neoteny in re hairiness?
It’s not so much that there’s an advantage to our hairlessness with respect to neoteny. Remember that the entire organism, and its associated genome, is what gets “selected”; natural selection does not pick and choose individual genes from a genome to continue on. Since neoteny itself was on the whole advantageous, hairlessness, being but one of a suite of associated features, would have “gone along for the ride”. The processes which resulted in our being neotenous in the first place (likely driven, at least in part, by our increase in brain size: as heads get bigger, it becomes necessary to squeeze out the offspring sooner, therefore they need to be less developed) were the focus of the selective process. Associated features were not necessarily themselves being selected for or against.
However, I don’t doubt that there was (or is) an inherent advantage to being less hairy than the “typical” ape, either. It would have just underscored the “good idea-ness” of the whole neoteny trend. It’s more a case that being relatively hairless turns out to be a workable solution (or, at the very least, not a hinderance), given where our ancestors evolved, than a case of hairlessness evolving specifically because of where our ancestors evolved.
I think we’ve covered most things like helpless children and weak pelvises and hairlessness - something better took their place.
But here’s another class of physical vulnerability. IMHO adult humans may be more physically more vulnerable to microbes, because we’ve avoided exposure due to not drinking out of puddles all our lives thanks to our greater intellegance ( ) so haven’t built up resistance. If we had have drunk dirty water we’d have lost more people but the ones left would be hardier. That is, this isn’t an evolutionary change, just environmental.