People who don't believe in Darwin's theory of evolution have a simple answer to all questions about why humans are markedly different from all other animals - God created everything. To people who believe in Darwin's theory and are interested, the questions pertaining to human evolution are intriguing and controversial. The aquatic ape hypothesis is very controversial within the scientific community but, as the author explains, it deserves serious consideration.
Most of us who believe in Darwin accept that there was once a species of ape living in Africa from which all people are descended as well as all modern apes such as gorillas and chimpanzees. Looking at the modern apes, we can observe some similarities with ourselves but there are also many obvious differences. Those apes are much hairier than us and often spend their time in trees. When they walk on the ground, they generally do so on four legs rather than two. Apes use body language far more than we do, yet our faces are much more expressive than theirs. Our noses are also very different from theirs. There are less obvious but equally important differences such as the location of the larynx. Of course, there are noticeable differences between different species of apes, but they have more in common with each other than any of them do with us.
The author suggests that there may have been a time when our ancestors were forced to adapt to a semi-aquatic lifestyle. On that basis, the likeliest scenario is that we are descended from a group of apes then living in Africa near the Red Sea, maybe around six or seven million years ago. The author doesn't mention the Sahara desert but I know from other sources that it is of more recent origin, maybe three or four million years old, so the region was very different before that. Geological changes, perhaps of a catastrophic nature, isolated these apes from the African mainland for a million years or two. During that period, they became increasingly reliant on fish and other aquatic food to supplement their diet. Initially, they navigated water simply by wading, hence the reason for walking on two legs, but they eventually learned to swim. The unusual noses they evolved, which we still have, enabled them to swim underwater for short periods. In deep water, the ability to use body language is limited (try jumping up and down in a swimming pool) so facial expressions developed.
Ultimately, whether due to further geological changes or the swimming ability that they'd acquired, the ape-men were able to return to the African mainland, eventually migrating down the Rift Valley to southern Africa. By that time, they looked very different from the apes that had been their ancestors although they didn't look exactly like us either, as more evolution of a less dramatic nature has taken place subsequently. Meanwhile, the mainland apes had followed their own evolutionary path and several different species had emerged. In the five million years plus that have elapsed since the ape-men returned to the mainland, our ancestors again adapted to a terrestrial existence but never quite lost the aquatic dimension. We may not spend much time in the water (except the minority who choose to do so) but we still eat fish and other aquatic food when we choose to.
Most of the book is taken up by an analysis of the various features of the human body that differentiate us from apes, looking at other species and noticing similarities with them. Our skin and its comparative lack of hair is more akin to whales, dolphins, elephants and domestic pigs than apes. Whales and dolphins both have terrestrial ancestors while elephants and pigs (like us) may once have had ancestors that adapted to a semi-aquatic life. The position of our larynx is comparable to that in a walrus. Our noses are not like anything found in any other creature but the nearest comparison is with a proboscis monkey, who also developed an unusual nose for use when wading. Sweat, tears and body fat all distinguish us from apes and all are discussed in detail. Walking on two legs draws comparison with some types of dinosaurs. After their mass extinction, no creatures except birds (who themselves evolved from dinosaurs beginning in the Jurassic period) ever walked primarily on two legs until our ancestors started doing so.
If the aquatic ape hypothesis is correct, it seems that our ancestors adapted quite well to a semi-aquatic life, but it must still have been very hard because they took the opportunity to return to terrestrial life when it eventually arose. After that, they must have been at some disadvantage initially compared to those apes that had continued evolving on the mainland. Perhaps those disadvantages (slowness and reduced sense of smell among them) forced them to find other survival strategies that, developed over a few million years, enabled us to become the dominant species on the planet. Those later developments including speech are outside the scope of this book, although the author points out that we could not have developed speech if our larynx position were similar to other apes.
Critics of the aquatic ape hypothesis point to a lack of definitive proof. Most books tell us that our ancestors moved directly from the forests to the open plains but this theory, also unproven, cannot convincingly explain the way we look. I look forward to the emergence of a credible alternative to the aquatic ape hypothesis that explains this, or to proof that the aquatic ape hypothesis is correct. The author provides a strong case for it. Though this book was published in 1997, it is possible to keep track of the latest research findings by surfing the net for aquatic ape.