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

     Now that we have established that there was, (despite the overall drying trend), enough water around for a semi-aquatic existence to be possible, we must ask what features would be expected if this occured. This is where the concept of convergent evolution becomes extremely important.

Why Bipedalism?
Good Reasons to Wade and Remain Near Water

     As stated previously, bipedalism must have come about in response to some severe environmental stress. It is possible that our early ancestors began their adaptation to bipedalism with initial wading behaviour, just as we see the modern macaques, probosis and capuchins doing. As it foraged for aquatic vegetation, and perhaps small crustaceans and mollusks, the little primate would soon discover it could wade deeper on two legs than four, thus expanding and exploiting available resources for food (Morgan 1997). This behaviour could have far-reaching consequences.

    This extra food source would be advantageous for the species, especially in times of reduced availability of an adequate food supply on land. As time went on, natural selection would have favoured those individuals who were most successful at exploiting all available food supplies. If food supplies on land were dwindling due to the drying of the African continent in the Pliocene, a primate with the ability to wade, swim and dive would have an upper edge over those who did not have this adaptation.

     In turn, their offspring over generations would become more adapted to an upright wading posture, resulting in lengthening of the legs, and realignment of the spine (Morgan 1997). Also, in a semi-aquatic food-rich environment, they would develop more "advanced" swimming and diving skills, to better exploit those resources. This could have easily made them physiologically unable to return to efficient quadruped locomotion, or the knuckle-walking of the great apes (Morgan 1997; Verhaegen 1999). It is important to keep food and resources in mind as a key driving force for the natural selection of those traits which would offer the best chance of overall species survival.

     Since bipedalism would have initially been a handicap, far slower than running on all fours, the drive to become bipedal must have been very strong in order for a species to be forced to adopt it. If one considers the habitat of our early ancestors to be at the land-water interface (eg. gallery forests, river deltas, coastal regions), there is no reason not to believe that this early primate would exploit, if at all possible, the nutritious riches of an aquatic environment. If this was the case, then our early ancestors were most likely aqua-borealists, who spent part of their time in the trees, the other in water. Water is the perfect environment to encourage an upright wading posture. In Australopithecus afarensis (Lucy), a bipedal hominid, there is still evidence of aboreal activity in the hands, which may indicate an aqua-boreal existance (Verhaegen 1999). As the species over time became larger, the aboreal lifestyle ended, and the bipedal walking and wading took over.
    There are primates living today who frequent the water, and all do so bipedally. A good example is the Probosis monkey, pictured here to the right. It frequently wades through the waist deep waters of the tidal mangrove swamps of Borneo.
Females making the trek, do so holding their babies against their chests, not on their backs. They have also been seen walking bipedally when the tide is low, collecting mollusks and other tidal organisms which cling to the roots of the mangrove trees. They have been witnessed walking in single file, all bipedally from one feeding area to another (Morgan 1997).

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