The Role of Water in Human Evolution13

What Features Would be Expected in a Semi-Aquatic Ape -
Do We Have Them?

Bipedalism: Its Resulting Changes in Morphology

From left to right: Chimpanzee; Australopithecus afarensis; Homo sapiens sapiens

Over time, due to continued bipedalism, we see a change in the overall shape of the pelvis. The lateral dimensions open, and the vertical align. This is a feature binding all hominids together. This tilting of the pelvis is seen also in many aquatic mammals (Morgan 1997). Partly due to the angle at which the head is held when the animal is vertical in the water or horizontal and swimming.
This change in the pelvis in turn effects the shape of the femur, as continued adaptation to bipedalism over time occurs:

From left to right: Chimpanzee; Australopithecus afarensis; Homo sapiens sapiens Note the subtle differences in the shape and positioning of the top of the femur.

From left to right: Chimpanzee; Australopithecus afarnesis; Homo sapiens sapiens
An obvious change in foot morphology is clearly seen as hominids became more fully adapted to a bipedal form of locomotion. The foot of the chimpanzee, Pan. troglodyte, appears much more hand-like than either the Homo or A. afarensis foot. Elongation and straightening of the thumb and "fingers" is already established in A. afarensis, clearly a foot made for walking. It has been suggested that the filling in of the toes may have began as some kind of "webbing", allowing for greater speed while swimming (Morgan 1982), although this difficult to prove. The skull has also changed over time, as seen below. The area where the spine enters the cranium has moved markedly forward towards the center from A. afarensis to Homo sapiens. This indicates a more upright posture developing over time. A posture which we are still struggling with. Back and neck problems in humans are some of the prevelant health complaints.
Pan. trogolodyte; Chimpanzee	Australopithecus afarensis	Homo sapiens sapiens
Skull of Pan. troglodyte, common chimpanzee. Note the extended jaw, with large developed canines, lack of a chin, small cranium and strong orbital ridge (browbone). The face is concave, and the over all appearance is bottom-heavy.	Skull of A. afarensis, "Lucy". Notice here the increased cranium, and the shortened jawline. The canines are also very much smaller that those of the modern chimp. No chin, and deeply sloped forehead.	Skull of Homo sapiens sapiens, modern human, well-developed chin, large cranium, small jaw, and small canines. Very little orbital ridge, strong cheekbones, no sloping of the forehead.

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From left to right: Chimpanzee; Australopithecus afarensis; Homo sapiens sapiens
Over time, due to continued bipedalism, we see a change in the overall shape of the pelvis. The lateral dimensions open, and the vertical align. This is a feature binding all hominids together. This tilting of the pelvis is seen also in many aquatic mammals (Morgan 1997). Partly due to the angle at which the head is held when the animal is vertical in the water or horizontal and swimming. This change in the pelvis in turn effects the shape of the femur, as continued adaptation to bipedalism over time occurs:
From left to right: Chimpanzee; Australopithecus afarensis; Homo sapiens sapiens	Note the subtle differences in the shape and positioning of the top of the femur.