Evolution
Why do humans differ from apes so much?
Scientists find it easy to explain why we resemble the African apes so closely by pointing out that gorillas, chimpanzees and humans share a common ancestor.
It is much harder to explain why we differ from the gorilla and the chimpanzee much more markedly than they differ from one another. Something must have happened to cause one section of the ancestral ape population to proceed along an entirely different evolutionary path.
The most widely held theory, still taught in schools and universities, is that we are descended from apes which moved out of the forests onto the grasslands of the open savannah. The distinctly human features are thus supposed to be adaptations to a savannah environment.
In that case, we would expect to find at least some of these adaptations to be paralleled in other savannah mammals. But there is not a single instance of this, not even among species like baboons and vervets, which are descended from forest- dwelling ancestors.
This awkward fact has not caused savannah theorists to abandon their hypothesis, but it leaves a lot of problems unanswered. For example, on the question of why humans lost their body hair, it has been argued at various times that no explanation is called for, or that we may never know the reason, or even that there may not be a reason. These attitudes seem to be not merely defeatist, but fundamentally unscientific.
The Aquatic Ape Theory (AAT) offers an alternative scenario. It suggests that when our ancestors moved onto the savannah they were already different from the apes; that nakedness, bipedalism, and other modifications had begun to evolve much earlier, when the ape and human lines first diverged.
AAT points out that most of the "enigmatic" features of human physiology, though rare or even unique among land mammals, are common in aquatic ones.
Point #1: Why the hell are we naked?
Out of the hundreds of living primate species only humans are naked. Two kinds of habitat are known to give rise to naked mammals - a subterranean one or a wet one. All other non human mammals which have lost all or most of their fur are either swimmers like whales and dolphins and walruses or wallowers like hippopatamuses and pigs.
It was suggested that humans became hairless to prevent overheating in the savannah but no other mammal has ever resorted to such a strategy. A covering of hair acts as a defense against the heat of the sun which is why even desert dwelling camels retain their fur. What seems undeniable is that while a coat of fur provides the best insulation for land mammals the best insulation in water is not fur but a layer of fat.
Point #2: I love my love handles
Humans are by far the fattest primates. There are two kinds of animals which tend to acquire large deposits of fat - hibernating ones and aquatic ones. In hibernating animals the fat is seasonal and in aquatic ones, as it is in humans, it is present all year round. Also, in land mammals the fat tends to be stored internally whereas in aquatic mammals and in humans the fat is mostly subcutaneous fat (stored under the skin).
It is unlikely that early man would have evolved into a fatter version because it would have slowed him down. No land based predator would want to get fat. All infant primates except our own are slender because they need to cling to their mothers and support their whole weight with their fingers. Our babies accumulate fat even before birth and continue to grow fatter for several months afterwards. Some of this fat is white fat and that is extremely rare in new born mammals. White fat is not good for supplying instant heat and energy. It is however good for insulation in water and for giving bouyancy.
Point #3: Mamma what a big brain you have
The most widely discussed contrast between ourselves and the apes is that we have bigger brains. A bigger brain may well have been an advantage to early man but it would have been of an advantage to a lot of animals. Why did humans aquire it? The answer is probably diet. The building of brain tissue in humans is dependent on an adequate supply of Omega-3 fatty acids which are abundant in the marine food chain but relatively scarce in the land food chain.
Point #4: Walking Upright - this helps how?
Bipedalism is very rare with mammals. Compared with running or walking on four legs it has many disadvantages. It is slower, relatively unstable, and a skill that takes many years to learn. It also exposes vital organs to attack. Only some powerful pressure could have caused our ape ancestors to adopt such a way of walking to which they were so ill suited.
If perhaps the ape's habitat had become flooded, they would have been forced to walk on their hind legs whenever they came down to the ground in order to keep their heads above water. The only animal which has ever evolved a pelvis like ours was the long extinct oreopithecus, known as the swamp ape.
Today two primates when on the ground stand and walk erect somewhat more readily than most other species. One, the proboscis monkey, lives in the mangrove swamps of Borneo. The other is a bonobo or pygmy chimpanzee, its habitat includes a large tract of seasonally flooded forest, which would have covered an even more extensive area before the African climate became drier. Both of those species enjoy the water.
Point #5: Conscious control of breathing
The human respiratory system is unlike any other land mammal's in two respects. The first is that we have conscious control of our breathing. In most mammals this is involuntary, like the heart beat or process of digestion. Voluntary breath control appears to be an aquatic adaptation because, apart from ourselves, it is found only in aquatic mammals like seals and dolphins. When they decide how deep they are going to dive, they can estimate how much air they need to inhale.
Point #6: The descended larynx - don't go down the wrong hole
Another human peculiarity is the fact that we have a descended larynx. A land mammal is normally breathing through its nose because its windpipe passes up through the back of the throat and the top of it (the larynx) is in the back of its nasal passages. Darwin found it puzzling that our larynx descends into our throat because it means that the opening to the lungs will then lie side by side with the opening to the stomach. That is why in our species food and drink may sometimes go "down the wrong hole". If we had not evoloved an elaborate swallowing mechanism it would happen every time.
By having a descended larynx humans can breathe through their mouths as easily as through their noses. This is probably an aquatic adaptation because a swimmer needing to gulp air quickly can inhale more of it through the mouth than the nostrils. The only mammals with a descended larynx apart from humans are aquatic ones such as the sea lion and the dugong.
Point #7: The Vernix Caseosa
It is a waxy white substance found coating the skin of newborn humans. It is composed of sebum (the oil of the skin) and cells that have soulghed off the fetus' skin. It has been hypothesised that it protects the baby's skin from dehydration in the womb. Without the vernix, the baby would have very wrinkled skin from constant exposure to the watery amniotic fluid. No other land mammal produces this but some sea mammals, including the harbour seal do.
There's a bunch of other things, but those were the most interesting to me. I wonder why I never heard much about this Aquatic Ape theory.
Scientists find it easy to explain why we resemble the African apes so closely by pointing out that gorillas, chimpanzees and humans share a common ancestor.
It is much harder to explain why we differ from the gorilla and the chimpanzee much more markedly than they differ from one another. Something must have happened to cause one section of the ancestral ape population to proceed along an entirely different evolutionary path.
The most widely held theory, still taught in schools and universities, is that we are descended from apes which moved out of the forests onto the grasslands of the open savannah. The distinctly human features are thus supposed to be adaptations to a savannah environment.
In that case, we would expect to find at least some of these adaptations to be paralleled in other savannah mammals. But there is not a single instance of this, not even among species like baboons and vervets, which are descended from forest- dwelling ancestors.
This awkward fact has not caused savannah theorists to abandon their hypothesis, but it leaves a lot of problems unanswered. For example, on the question of why humans lost their body hair, it has been argued at various times that no explanation is called for, or that we may never know the reason, or even that there may not be a reason. These attitudes seem to be not merely defeatist, but fundamentally unscientific.
The Aquatic Ape Theory (AAT) offers an alternative scenario. It suggests that when our ancestors moved onto the savannah they were already different from the apes; that nakedness, bipedalism, and other modifications had begun to evolve much earlier, when the ape and human lines first diverged.
AAT points out that most of the "enigmatic" features of human physiology, though rare or even unique among land mammals, are common in aquatic ones.
Point #1: Why the hell are we naked?
Out of the hundreds of living primate species only humans are naked. Two kinds of habitat are known to give rise to naked mammals - a subterranean one or a wet one. All other non human mammals which have lost all or most of their fur are either swimmers like whales and dolphins and walruses or wallowers like hippopatamuses and pigs.
It was suggested that humans became hairless to prevent overheating in the savannah but no other mammal has ever resorted to such a strategy. A covering of hair acts as a defense against the heat of the sun which is why even desert dwelling camels retain their fur. What seems undeniable is that while a coat of fur provides the best insulation for land mammals the best insulation in water is not fur but a layer of fat.
Point #2: I love my love handles
Humans are by far the fattest primates. There are two kinds of animals which tend to acquire large deposits of fat - hibernating ones and aquatic ones. In hibernating animals the fat is seasonal and in aquatic ones, as it is in humans, it is present all year round. Also, in land mammals the fat tends to be stored internally whereas in aquatic mammals and in humans the fat is mostly subcutaneous fat (stored under the skin).
It is unlikely that early man would have evolved into a fatter version because it would have slowed him down. No land based predator would want to get fat. All infant primates except our own are slender because they need to cling to their mothers and support their whole weight with their fingers. Our babies accumulate fat even before birth and continue to grow fatter for several months afterwards. Some of this fat is white fat and that is extremely rare in new born mammals. White fat is not good for supplying instant heat and energy. It is however good for insulation in water and for giving bouyancy.
Point #3: Mamma what a big brain you have
The most widely discussed contrast between ourselves and the apes is that we have bigger brains. A bigger brain may well have been an advantage to early man but it would have been of an advantage to a lot of animals. Why did humans aquire it? The answer is probably diet. The building of brain tissue in humans is dependent on an adequate supply of Omega-3 fatty acids which are abundant in the marine food chain but relatively scarce in the land food chain.
Point #4: Walking Upright - this helps how?
Bipedalism is very rare with mammals. Compared with running or walking on four legs it has many disadvantages. It is slower, relatively unstable, and a skill that takes many years to learn. It also exposes vital organs to attack. Only some powerful pressure could have caused our ape ancestors to adopt such a way of walking to which they were so ill suited.
If perhaps the ape's habitat had become flooded, they would have been forced to walk on their hind legs whenever they came down to the ground in order to keep their heads above water. The only animal which has ever evolved a pelvis like ours was the long extinct oreopithecus, known as the swamp ape.
Today two primates when on the ground stand and walk erect somewhat more readily than most other species. One, the proboscis monkey, lives in the mangrove swamps of Borneo. The other is a bonobo or pygmy chimpanzee, its habitat includes a large tract of seasonally flooded forest, which would have covered an even more extensive area before the African climate became drier. Both of those species enjoy the water.
Point #5: Conscious control of breathing
The human respiratory system is unlike any other land mammal's in two respects. The first is that we have conscious control of our breathing. In most mammals this is involuntary, like the heart beat or process of digestion. Voluntary breath control appears to be an aquatic adaptation because, apart from ourselves, it is found only in aquatic mammals like seals and dolphins. When they decide how deep they are going to dive, they can estimate how much air they need to inhale.
Point #6: The descended larynx - don't go down the wrong hole
Another human peculiarity is the fact that we have a descended larynx. A land mammal is normally breathing through its nose because its windpipe passes up through the back of the throat and the top of it (the larynx) is in the back of its nasal passages. Darwin found it puzzling that our larynx descends into our throat because it means that the opening to the lungs will then lie side by side with the opening to the stomach. That is why in our species food and drink may sometimes go "down the wrong hole". If we had not evoloved an elaborate swallowing mechanism it would happen every time.
By having a descended larynx humans can breathe through their mouths as easily as through their noses. This is probably an aquatic adaptation because a swimmer needing to gulp air quickly can inhale more of it through the mouth than the nostrils. The only mammals with a descended larynx apart from humans are aquatic ones such as the sea lion and the dugong.
Point #7: The Vernix Caseosa
It is a waxy white substance found coating the skin of newborn humans. It is composed of sebum (the oil of the skin) and cells that have soulghed off the fetus' skin. It has been hypothesised that it protects the baby's skin from dehydration in the womb. Without the vernix, the baby would have very wrinkled skin from constant exposure to the watery amniotic fluid. No other land mammal produces this but some sea mammals, including the harbour seal do.
There's a bunch of other things, but those were the most interesting to me. I wonder why I never heard much about this Aquatic Ape theory.