An alternative to ST and AAT
Newington Reference Library (fp96@dial.pipex.com)
Thu, 17 Oct 1996 17:15:24 +0000
A NEW APPROACH TO THE PROBLEM OF HUMAN EVOLUTION
by Andrew Lewis
The Savanna Theory (ST) and the Aquatic Ape Theory (AAT) both make
certain assumptions that need to be challenged.
Both believe that our remote ancestors stopped living in one environment
(the forest) and started living in another (either the savanna or the
coastline).
Another possibility is that our ancestors evolved to become more
adaptable, to be able to exploit different environments seasonally. They
could have moved between at least three different environments to exploit
the seasonl abundance of each.
When the East African forest diminished, it did not do so evenly. In the
river valleys the forest remained. Where the river approached the sea,
the valley became wider and such features as delta formation, meandering
and braiding allowed for the forest to become more extensive.
I can imagine our ape ancestors becoming concentrated in these valleys,
especially closer to the sea. Each valley would eventually have become
an 'island' separated by expanses of grassland. The forest would have
continued to provide food for the apes, but only at certain times of the
year. It would have become more seasonl compared to the rain forest that
still exists in West Africa. At other times of teh year, the apes would
have gone hungry.
They would have ventured out of the valley in search of food. Sometimes
they would have moved along the coastline. Sometimes they would have
moved on to the savanna and the savanna-mosaic. In time they would have
learned and remembered when each environment offered the best resources
in each season, and seasonal patterns of movement were established.
Rivers and lakes, swamps and mud flats are also possible food sources.
Chimpanzees and bonobos are the most adaptable of animals apart from man.
Our ape ancestors were adaptable, and we developed this even further.
Three qualities made us so uniquely adaptable
1. Our behaviour became even less dependant on instinct and more
dependant on learning and reason.
2. We were omnivorous.
3. We developed physiological adaptations that allowed us to exploit all
three different environments.
The greatest physiological changes we needed to make were those
which allowed us to exploit the coastline environment, because that was
the environment that was the most different from that of forest-living
apes.
That is why it seems as if most of the differences between apes and
humans can be explained as aquatic adaptations.
We have lost specific adaptations to forest life, such as curved finger
bones that assist in gripping branches.
Our loss of forest-specific adaptations and our gain of aquatic
adaptations is misleading. It leads us to believe that our ancestors
left the forest and moved to the sea. I believe that we evolved to
become good all-rounders. We never 'left the forest', not altogether.
Humans have good tree-climbing abilities, especially in parts of the
world where such qualities are useful, and children all over the world
love to climb trees.
My theory disposes of the need to think of an 'aquatic phase' that ended
as man abandoned the coast to live inland. I believe that the coastal
regions of East Africa have provided the site of human evolution from the
time of our ape ancestors up to recent times.
When Europeans started to sail around the world 500 years ago they found
people living by the sea and from the sea wherever they went. If our
remote ancestors stopped living by the sea, when and why did they return
to become the ancestors of Polynesians, Strandloopers, Tierra del
Fuegans, etc.? Surely it is more reasonable to suppose that some humans
have always lived by the sea, at least for part of the year. The fact
that other humans lived in the interior does not alter this.
The presence of early modern humans at Klasies River Mouth in South
Africa, clearly living from the sea, supports this.
Population increase in a successful species such as our own would mean
that not everyone could live in the prime location of a river estuary.
They would have to compete, and the losers would have to learn to live
with a less than ideal environment. We were adaptable enough to be able
to do this. In this way the interiors of continents were colonised, with
rivers and the Rift Valley being settled first.
This would mean that modern humans have more aquatic adaptations that any
of our ancestors. We have more aquatic adaptations than the archaic Homo
species, who in turn had more aquatic adaptations than the
Austalopithecines. If the 'aquatic phase' theory is true then the
opposite would be the case.
The study of mitochondrial DNA suggest that all humans alive today
are descended from a small group of people living in Africa perhaps as
little as 100,000 years ago. I suggest that they evolved on the
coastline of East Africa, not the interior.
My own theory solves such problems as why have humans never re-evolved
fur. If a naked skin is unsuitable for a savanna existence, and so would
not have evolved on the savanna, why did it remain when our ancestors
supposedly went to live on the savanna full time? All humans have
maintained the physical type most suitable for existence in several
different environments.
My theory does not depend upon a dramatic change in climate to explain
our evolution. Our increase in adaptability is merely a continuation of
ape and especially chimpanzee adaptability. Therefore my theory is not
challenged by recent new information, suh as the fact that our ancestors
became bipedal well before East Africa became drier and savannas spread.
A small increase in the seasonality of the forest, together with more
variation in habitat, would be enough to favour ever more adaptable apes.
Also, difficult questions for AAT, such as
1. Was there enough time for our remote ancestors to have evolved an
aquatic way of life during an 'aquatic phase', considering possible time
scales?
2. Why would an aquatic ape want to abandon the aquatic way of life for
the savanna?
are not a problem for my theory.
Several people have suggested that AAT and ST are not mutually exclusive
eg. john Gribbin, Jeremy Cherfas and Sarah BM Kraak. My theory is an
elaboration of this.
It is only natural to think that each species of animal has one
environment to which it is adapted. However, many species are adaptable,
eg. the elephant. Elephants can live a semi-aquatic lifestyle in a
suitable environment, and they can also live in near desert conditions
where the may have to migrate long distances. They are long-lived,
social and intelligent, just like us.
I do not regard my theory, which I call the Multi Habitat Theory (MHT),
as a contradiction of AAT. It agrees with it on one point, that many of
the differences between man and ape are aquatic adaptations. I realise
that there is as yet no proof for it, but there is also no proof for AAT
and especially ST. The more information we have, the more we realise the
need for an alternative to ST: I believe my theory makes a contribution
to the debate.
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