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quote:Originally posted by GordonPHow does an ape, so dependent on trees for survival, suddenly survive on the open grasslands?
quote:Mountain Gorillas have longer and darker hair than other gorillas, enabling them to live at high altitudes and travel into areas where temperatures drop below freezing. They have adapted to a life on the ground more than any other non-human primate, and their feet most resemble those of humans. Gorillas can be identified by nose prints unique to each individual. Researchers often use photographs and illustrations of noses for identification and monitoring.
quote:The fossil skull TH 266, nicknamed "Toumaï" ("hope of life" in the local Goran language of Chad), may be a common ancestor of humans and chimpanzees; most molecular clocks suggest humans and chimps diverged 1–2 million years after S. tchadensis (5 mya). The original placement of this species as a human ancestor but not a chimpanzee ancestor complicated the picture of the human family tree. In particular, if Toumaï is only a direct human ancestor, its facial features bring the status of Australopithecus into doubt because the thickened brow ridgers are similar to later hominids, but not earlier ones. Another possibility is that Toumaï is anatomically related to both humans and chimpanzees, but the ancestor of neither. Brigitte Senut, the discoverer of Orrorin tugenensis, claims that the features of S. tchadensis are consistent with a female proto-gorilla.If Senut's claims are true the find would be especially significant; there have been no chimp or gorilla ancestors to be found anywhere in Africa and light would be shed on their family trees. What the find does show is that the last common ancestor of humans and chimpanzees is unlikely to resemble chimpanzees very much, as had been previously supposed.
quote:Originally posted by GordonPOne possible answer to this question is so politically incorrect, so soaked in sex and violence, that I hesitate to offer it before properly examining other explainations.
quote:Originally posted by GordonPInteresting discussion. Try this for another hypothetical senario.The climate in North Africa starts to change, as the years pass the forest retreats to central Africa and all the apes, dependent on the trees for safe haven, retreat with the forest. One particular species begin to spend most of their time on the fringes of the forest, already a user of tools (they use stones to break open nuts)they begin to scavenge on the remains of kills left by the preditors that now inhabit the open areas, using their tools to break open the bones which remain behind in order to get at the bone marrow.They live in small family groups led by a dominant male, usually the biggest and strongest male. The groups comprise, the dominant male, several adult females, the young and several adult subordinant males. The dominant male regards the adult females as his wives and guards them from the other males. They are still reliant on the trees for safe haven from preditors and only venture onto the open ground while one of the group is in position high in the trees as a watchout.So far nothing has happened to effect the evolution of the species.One day a male is born with a slight mutation, nothing spectacular, just a deformation of the pelvic bone. He still moves about most of the time with his knuckles almost brushing the ground but he can do something none of the rest of the group can do, he can take many steps in an almost upright position, the rest of the group can manage only three or four steps in this position before dropping their hands to the ground. (As with many apes today).Eventually he approaches maturity and driven by testosterone challenges the dominant male. Not yet fully mature his chances of success are practically nil and being something of a lightweight will probably always remain so.As the two face each other he does something that has never been done before, he picks up a short stout piece of broken branch, stands almost upright and closes in on the dominant male who also stands almost upright in defiance. After a very short while dancing around the dominant male can stand upright no longer and drops his hands to the ground, he is now defenceless. The young male knocks seven bells out of him and takes over the harem.Something new has happened, an ape has used a tool as a weapon, and changed the path of evolution. Now it is not the biggest and strongest who rules but the one who can stand upright the longest. As the ruler of the group has the females to himself his genes will predominate the next generation and so on and so forth.G W Pipes
quote:Originally posted by xethoPeople didn't evolve from apes, we shared a common ancestor.That common ancestor wasn't overly specialized for a life in either a forested or open environment. The ones that ended up living primarily in grasslands eventually became humans, the ones that lived in forests became monkeys.
quote:Originally posted by thebrain13I think the key issue is defense. It's been brought up that taller creatures can see more prey, but on the flip side more predators can see you. if you look at when the dinosaurs roamed the earth you might notice that most of the carnivores walked upright, while most of the herbivores walked on all four.
quote:The diet is another advantage to walking upright. Herbivores need to eat a lot more then carnivores so they have more weight to carry around.
quote:Originally posted by another_someonequote:Originally posted by thebrain13I think the key issue is defense. It's been brought up that taller creatures can see more prey, but on the flip side more predators can see you. if you look at when the dinosaurs roamed the earth you might notice that most of the carnivores walked upright, while most of the herbivores walked on all four.This no doubt explains why giraffes and elephants are so short, and why kangaroos walk on all fours, or why lions walk on their hind legs.quote:The diet is another advantage to walking upright. Herbivores need to eat a lot more then carnivores so they have more weight to carry around. This part is true, so carnivores tend to be sleeker, but they are no more likely to be bipedal (in fact, a bipedal cheetah would not run as fast).Back to your issue of defence, there is one point that may be relevant, and that is communal defence. Many social animals will post lookouts that give the social group an early warning of danger, and allow them time to prepare a communal defence against the threat. For these animals, particularly given the high visibility that inevitably derives from having a large community of animals congregating together, early detection of a threat is more important that camoflage.George
quote:Originally posted by thebrain13my point on defense was if you can defend yourself you can afford to be seen. Ive never seen any creature try to attack full grown elephants and girraffes. And as far as the evolution of marsupials in australia, well thats another debate.
quote:Lastly lets not forget that dinosaurs had much longer to evolve than mammals, the giant asteroid sent them back in evolution.
quote: walking upright is a more advanced feature.
quote: Im sure if there were raptors and giant tyrannosaurs walking the earth today, girraffes elephants and kangaroos would find themselves on the extinct list.
quote:There are differing views on how Lucy or her ancestors first became bipedal full-time.The so-called 'savanna theory' on how A. afarensis evolved bipedalism hangs on the evidence that around 6 to 8 million years ago there seems to have been a mass extinction of forest dwelling creatures including the oldest hominins recognizable: Sahelanthropus tchadensis and Orrorin tugenensis. This triggered a burst of adaptive radiation, an evolutionary characteristic that generates new species quickly. Lucy's genetic forebears were tree dwelling apes, but in Lucy's world the trees would have been much fewer, and Lucy would have been forced to find a living on the flat savanna. Being bipedal would have had evolutionary advantages. For example, with the eyes higher up, she could see further than quadrupeds. Bipedalism also saves energy. The disadvantages of bipedalism were great—Lucy was the slowest moving primate of her time, for example, but according to the hypothesis, the advantages of bipedalism must have outweighed the disadvantages.There had previously been problems in the past with designating Australopithecus afarensis as a fully bipedal hominine. In fact these hominines may have occasionally walked upright but still walked on all fours like apes; the curved fingers on A. afarensis are similar to those of modern-day apes, which use them for climbing trees. The phalanges (finger bones) aren't just prone to bend at the joints, but rather the bones themselves are curved. Another aspect of the Australopithecus skeleton that differs from human skeleton is the iliac crest of the pelvic bones. The iliac crest, or hip bone, on a Homo sapiens extends front-to-back, allowing an aligned gait. A human walks with one foot in front of the other. However, on Australopithecus and on other ape and ape-like species such as the orangutan, the iliac crest extends laterally (out to the side), causing the legs to stick out to the side, not straight forward. This gives a side-to-side rocking motion as the animal walks, not a forward gait.The so-called aquatic ape theory compares the typical elements of human locomotion (truncal erectness, aligned body, two-leggedness, striding gait, very long legs, valgus knees, plantigrady etc.) with those of chimpanzees and other animals, and proposes that human ancestors evolved from vertical wader-climbers in coastal or swamp forests to shoreline dwellers who collected coconuts, turtles, bird eggs, shellfish etc. by beach-combing, wading and diving. In this view, the australopithecines largely conserved the ancestral vertical wading-climbing locomotion in swamp forests ("gracile" kind, including Australopithecus afarensis and A. africanus) and later more open wetlands ("robust" kind, including Paranthropus boisei and P. robustus). Meanwhile, Plio-Pleistocene Homo had dispersed along the African Rift valley lakes and African and Indian ocean coasts, from where different Homo populations ventured inland along rivers and lakes. However, this theory is not taken seriously by anthropologists.
quote:thebrain13I think the key issue is defense. It's been brought up that taller creatures can see more prey, but on the flip side more predators can see you. if you look at when the dinosaurs roamed the earth you might notice that most of the carnivores walked upright, while most of the herbivores walked on all four.
quote:Some argue that if Tyrannosaurus were a scavenger, another dinosaur had to be the top predator in the Amerasian Upper Cretaceous. Top prey were the larger marginocephalians and ornithopods. The other tyrannosaurids share so many characteristics that only small dromaeosaurs remain a choice as top predators. In this light, scavenger hypothesis adherents have hypothesized that the size and power of tyrannosaurs allowed them to steal kills from smaller predators.
quote:The Secretary Bird is largely terrestrial, hunting its prey on foot, and besides the caracaras (such as Polyborus plancus) is the only bird of prey to do so habitually. Adults hunt in pairs and sometimes as loose familial flocks, stalking through the habitat with long strides. Prey consists of insects, small mammals, lizards, snakes, young birds, bird eggs, and sometimes dead animals killed in brush fires. Larger herbivores are not hunted, although there are some reports of Secretary Birds killing young gazelles.Young are fed liquified and regurgitated insects directly by the male or female parent and are eventually weaned to small mammals and reptile fragments regurgitated onto the nest itself. The above foodstuffs are originally stored in the crop of the adults.Secretary Birds have two distinct feeding strategies that are both executed on land. They can either catch prey by chasing it and striking with the bill or stomping on prey until it is rendered stunned or unconscious enough to swallow. Studies of this latter strategy have helped construct the possible feeding mechanisms employed by dinosaur-like terror birds that once walked the earth five million years ago.
quote:thebrain13many dinosaurs were warm blooded, and some had fur.
quote:thebrain13And I know mammals had technically the same amount of time to develope as dinosaurs, but mammals specialized in being smaller, dinosaurs specialized in being humongous. Dinosaurs had more time to develope as the largest creatures on earth. Mammals relatively recently adopted that role.
quote:Originally posted by GordonPOur direct ancestors, I'll call them "Ape type x" live in small family groups on the fringes of the forest. Each group is extremely territorial and any member of another group who strays into their territory is liable to get killed and eaten, unless the offender is female in which case she will be captured and added to the dominant male's harem.In this way each group is relitively isolated from the other groups almost as if each was on a separate island.Now let me original senario run.
quote:What you describe is pretty much how chimps behave anyway. It is not enough to create the level of isolation required.
quote:The first question you have to ask is whether the changes are sex linked or not. Since there is a sexual dimorphism in any species with regard to pelvic bone structure, there is little reason to believe that this change is linked to a sex gene. Thus, even with the regular influx of females from the outside, it would still quickly dilute and genetic abnormality in the pelvic bone structure of Ape type x.
quote:Originally posted by GordonPThe ancestors of chimps and the ancestors of my hypothetical type x lived different lifesyles. The chimps spent most of the time in the trees, where the use of a tool as a weapon offers no real advantages as both hands are needed to move quickly through the tree-tops. Type x spent most of the time on the ground where the ability to stand upright during combat with weapons offers massive advantages during a fight to establish who is the dominant male. The level of isolation required is maintained by cannibalism. Even as recently as a few hundred years ago cannibalism was practised by some humans.QuoteGorillas also spend their entire life on the ground, because they are just too heavy to climb trees. The difference is that they still live in the forest, so their visibility is limited, and everything they do is nearby. They also are herbivores (with the exception of a few insects), so they don't need to run after their food, whereas Chimpanzees are omnivores who do chase and hunt other monkeys (and even have been observed to resort to cannibalism).QuoteThe mutation of the hip bone would not be diluted because of the power the dominant male held. As undisputed leader of the group he would father most if not all of the next generation. (Getting to close to one of his females while he was anywhere near would lead to a bad beating or could be fatal).What happens in practice is that a male will hold on to a harem that is just as large as he can manage. What in fact this means is that he does not quite manage to hold on to this size of harem, and quite often some of the females will sneakily wonder off for a quickie with some other male. If the ground living apes and tree living apes can interbreed, there is no reason to assume that regular (if not frequent) interbreeding will not occur. Either a tree living ape will come down to the floor, quickly mate, and rush back up into the trees where the ground living ape cannot follow; or a tree living male will quickly drop down to the ground (while the dominant male) is distracted elsewhere, have a quickie with one of the females, before disappearing back up into the trees.Ofcourse, as I said, it depends upon whether the two groups can efficiently interbreed.The different in posture does have significant implications for breading. One different is ofcourse that humans are uniquely capable of mating face to face; but another difference is that all non-human female apes have a large pink vaginal swelling when they are on heat, whereas the upright posture of human females does not make that practical, and thus the ways in which a human male can tell if a human female is on heat must be different to that which most other apes use (humans use colour of cheeks and lips and size of breasts as important cues; although both human and non-human apes can still use smell, and ofcourse behavioural changes). If a male cannot properly tell that a female is on heat, then he will be less motivated to mate with her, and thus simply changing the cues for mating can often be enough to separate two groups into distinctly separate breeding groups.Ofcourse, none of this explains how one group became habitually tree living and another habitually ground living if they shared the same space, and were still interbreeding (what we have explained is that once they were separated into these two groups, they may not easily reintegrate – but the separation had to come about first, and this would most logically still require geographic isolation of a very small group).George
Gorillas also spend their entire life on the ground, because they are just too heavy to climb trees. The difference is that they still live in the forest, so their visibility is limited, and everything they do is nearby. They also are herbivores (with the exception of a few insects), so they don't need to run after their food, whereas Chimpanzees are omnivores who do chase and hunt other monkeys (and even have been observed to resort to cannibalism).QuoteThe mutation of the hip bone would not be diluted because of the power the dominant male held. As undisputed leader of the group he would father most if not all of the next generation. (Getting to close to one of his females while he was anywhere near would lead to a bad beating or could be fatal).
The mutation of the hip bone would not be diluted because of the power the dominant male held. As undisputed leader of the group he would father most if not all of the next generation. (Getting to close to one of his females while he was anywhere near would lead to a bad beating or could be fatal).