Paleoanthropologists have long-sought a missing link in the evolution of humans. Their collective efforts have continually focused on the Horn of Africa, the same location that revealed Lucy (Australopithecus afarensis). The area, encompassing Djibouti, Ethiopia, Eritrea and Somalia, is, if fossils can be taken as the evidence we'd all like it to be, the birthplace of the human species.

While the region of our special birth is not in dispute, the means by which we evolved, quite surprisingly, are.

The common theory, the one propounded in many a high-school text, is that we humans evolved on the savanna. It was on ancient grassy plains, as the Savanna Theory (ST) goes, that our ancestors took the first steps toward what we are today. Our early brethren stood up to see over the tall grasses, to spy for predators, or, perhaps, to find members of the group, or even to locate a wandering child.

Within the scope of this theory, then, all of our physical traits, our upright walking, our hairless bodies, our propensity to sweat, to name a few, evolved, through the process of Natural Selection, on the plains of Africa.

However, for as good of a job as this theory does in explaining our evolutionary history, there are numerous questions that it does not answer. In fact, though the debate is largely considered to be settled among anthropologists, there is small group of heretics who question whether we evolved in the grass at all.

The origins of these heretical questions come primarily from one source, The Aquatic Ape Theory (AAT). In her 1982 book of a similar name Elaine Morgan proposes that the impetus for our evolution was an environment far different than the one commonly reported. Our ancestors, she says, did not spend their time foraging on the plains, but rather in marshes and swamps.

To support her claim Morgan relies on simple observation of humans, our relatives, and the holes in the Savanna Theory. These observations and inconsistencies form the basis of one of the most compelling, and least reported, human evolutionary theories. This article will not attempt to enumerate all of the points Morgan makes in her book. Instead it will highlight just a few on the more interesting examples.

Hairlessness:
Modern humans are fairly hair free animals. Nearly hairless when compared to our relatives on the primate tree. The reason for this, according to ST is the hot, arid environment of the plains. While there, our ancestors slowly lost their hair to compensate for the heat.

Curious, the AAT points out, is the distribution of hair that does exist on our bodies. The head, where the bulk of our hair is located, generates a large amount of heat that must be expelled for the brain's sake. Why, the AAT asks, would we evolve to retain head hair and thus heat, but lose the rest?

The answer could be that our distant relatives were in an environment that required them to keep their heads warm. If we began in the water, with just our heads protruding, then our head hair could be a trait designed to keep the head warm and protect the delicate skin from the sun.

Similarly, the AAT asks us to consider the paucity of primates without body hair, but relatively large number of aquatic mammals that do lack it. Dolphins and whales lost their hair as an adaptation to their surroundings. Perhaps, says AAT, we did the same.

Omega-3:
Our brains require enormous amounts of the fatty-acid Omega-3. This chain of carbon molecules helps our brains to function and, strikingly, is lacking in the diet of our primate relatives. In fact, according to AAT, it is safe to assume that with what our ancestors would have had to eat on the savanna we wouldn't have evolved into what we are today.

Fish, and specifically shellfish, however, have Omega-3 in abundance. They are, even today, one of the best sources of it. A species of proto-humans, living an aquatic life-style would have had access to large quantities of shellfish. According to AAT, this environmental factor would have influenced our evolution and steered us toward larger, more complex brains.

Sex Position:
There are a limited number of species that have sex in what is colloquially referred to as the Missionary Position. Humans and bonobo monkeys (who will do it any which way as often as possible) are two in the even smaller number of land-based mammals who do so.

However, among aquatic mammals, this kind of face-to-face copulation is decidedly normal. A life in the water requires certain adaptations, including the repositioning of the vagina to a lower and more recessed locale to prevent water from entering while swimming. This trait is shared by most aquatic mammals, and by humans.

The female sex organ being more out of the way necessitates face-to-face copulation to ensure penetration. In light of this, AAT asks us to consider how odd it is that one species of primate, which supposedly evolved upon a plain, would have this physical trait in common with so many other animals from an entirely different environment.

Bi-pedal Movement:
One of humanity's most defining characteristics is our unique ability to walk upright, on two legs. Though there are a few species that perambulate on two feet there are no other species of primate that do so with any regularity. For, while apes have been observed to stand, and even walk, on their hind legs they only do so for small amounts of time.

However, AAT notes with enthusiasm that apes will consistently stand up when entering the water. Once submerged the massive chest and torso are supported by the water, freeing up the legs to move more easily.

To AAT supporters this suggests an alternative to our species' savanna-specific attributes. Evolution, they note, moves slowly. So slowly that an early human would derive little value from standing on a plain. The legs would become tired quickly, during the brief attempts to stand. And with out a pressing environmental spur like water, say AAT adherents, there would have been no need to stand constantly, and thus develop the trait that makes us, well, stand out, against the rest of the animal kingdom.

However, despite all of the weight in its corner, the Aquatic Ape Theory lacks something no serious scientific theory should be without: physical evidence. The environs our possibly aquatic brethren might have lived in would most likely have been swamps or marshes. These two places do not lend themselves to the preservation of fossils.

Without tangible proof to support their claims, AAT adherents are left with a theory that does not stand up to the rigors of science. A theory detractors insist should be relegated to the dubious field of cryptozoology.

Yet there is, perhaps, another reason the Aquatic Ape theory hasn't gained a toehold in the public consciousness. Living in a swamp just isn't all that sexy. Though both theories are incomplete, at best, the Savanna Theory might win out in the end because it provides a much more enticing setting for the birthplace of humanity, and the evidence to back it up.

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