The Aquatic Ape Theory - Why it Works

Some time ago, I submitted an answer to New Scientist's "The Last Word" regarding a question about why humans have outward facing protuding noses while "our primate brethren seem to manage with relatively flat faces) and my answer was published here, and is available here for those without New Scientist subscriptions (and I do find it ridiculous that they charge even for the Last Word). Some poor intern at the Daily Mail also seemed to mistake me for some kind of authority on human evolution, after quoting me on their loose article on the Aquatic Ape theory, vaguely describing me "a biology researcher" in their article. 
Since the expansion of the internet, this article has bounced around a bit and I've seen the odd facetious comment by some who think the Aquatic Ape theory is codswallop, and they have managed to find some chink in the armour of the hypothesis (I mean this only as a loose term, since physical evidence is difficult to come by, as we shall discuss later. But nevertheless, of course, it is true). 
I ended up writing the answer after seeing the question and immediately I recognised that the nose is one of the main pieces of evidence that we have for the aquatic ape theory, and suspected that due to lack of popularity, very few would come up with such an answer. I saw an opportunity to advertise the theory and knew I had to put pen to paper (or fingertips to keyboard buttons, in this case). 
I first came to love the aquatic ape theory when I was a late teenager and I got my hands on Desmond Morris' "The Naked Ape". This is a wonderful book, with a titilating title, but that is full of intrigue, twists and turns and is as charmingly and wittily written as any romance novel you might be considering to take on holiday with you this year. And please, may I urge you, take this book. It is a wonderful, wonderful book, that makes sense of aspects of humanity that you didn't even realise were strange, starting from the basic premise of the book which is, why is it that if you lined up all of humanity next to all of its closest ancestors, from higher apes, primates and monkeys, the human would stick out like a sore thumb on account of it being largely hairless? It is written in such an entertaining way by the charismatic yet informative Morris, that I can't fathom why he isn't a national treasure. Someone please give this man an OBE for making science fun and accessible. 
It was clear to me after reading this book, that many aspects of human physiology only made sense in light of the Aquatic Ape Theory, and the key features are quite competently described in the otherwise dubious Daily Mail article : 
1) The baby larynx reflex that prevents them from accidental drowning at an age where they're otherwise physically poorly coordinated
2) The retention of hair on our heads
3) The fact that our nearest relatives, chimps, who we differ from by less than 1 % of our genome can't stand to dip their feet in water
4) The unusually protruding noses
I've even been able to add another physiological factor to the list that I recently heard:
5) Have you ever wondered why our fingertips and toes go wrinkly after an extended amount of time in the water? Well, in fact, it's been shown that this rippling effect increases grip in slippery and wet surfaces! So clearly, our ancestors were wading around in the water for something long enough for such a characteristic to develop (I'm betting it was for mussels and crabs, but clearly, I've since lost the gene that creates an appetite for such dishes!)
Isn't the human body such a wonderful thing? To think that all these parts of our bodies that we never think about have adapted in such a specific way to make our lives easier. I will never understand how "unweaving the rainbow" can make it less beautiful. I believe that by further understanding the world, or our bodies, in this case, we can truly begin to appreciate what it does for us, and not take it for granted. 
The Aquatic Ape theory doesn't even stop there. It has been proposed that by wading in water, the support to the limbs facilitated the transition of quadrupedal ape ancestors into the bipedalism which has made us so successful. 

Japanese macaques washing sweet potatoes in the sea

So, getting back to the rebuttals:
1)  "If the Aquatic Ape theory is true, then why don't we all have blowholes on the top of our heads/flippers instead of arms/other cetacean feature, just like dolphins/whales?" 
This is one of the most common rebuttals I've seen, but also one of the easiest ones to explain. Cetaceans are formerly land-dwelling mammals that around 50 million years ago, decided to make the migration back into the sea, after deciding that the land wasn't for them. They made a permanent change to an exclusively aquatic lifestyle, that has lasted longer than the evolution of primates. By comparison, when cetaceans made this move, we were not only not "out of Africa" at that point, but the primates had not even split into new world and old world monkeys. The first hominids didn't appear until 15 million years ago, and the famous Homo erectus didn't make an appearance until 1.8 million years ago. Although the dates are contentious, anatomically modern humans didn't appear in the fossil record until 160,000 years ago, and the so-called "mitochondrial Eve" who is the earliest known modern ancestor to all humans has been calculated to have lived approximately 150,000 years ago. 
Now, I don't know about you, but that seems to give cetaceans a bit of a head start on evolving water-appropriate traits. Evolution is slow. So slow in fact, that most people can't see it happening with their eyes, which is why they choose not to believe it (although for some reason, not seeing a deity doesn't stop them believing in religion). 
What we're talking about here in the AAT, is that at some point, maybe around 5 million years ago to Homo erectus time, there was a time period during which, human ancestors consistently inhabited environments next to bodies of water, and made heavy use of the water environment. So, while we both lost body hair and developed a thicker layer of subcutaneous fat on our way to the oceans, cetaceans have had more time to develop even more highly specialised adaptations for aquatic living (although it must have been a shock when the mother cetacean gave birth to the first ever cetacean baby with a blow hole. Or did the nose just slowly migrate to the top of the head over millions of years?).

How did my nose get all the way up there?

The second point is that cetaceans made the move back to water, permanently, never to return to land at any point in their life cycle. Indeed, when cetaceans become stranded on land due to freak ocean currents or tides, it usually means certain death, unless they can be moved back by some helpful (and usually very strong) hominids. There is a misunderstanding that the AAT means humans also lived in a solely aquatic environment. When some people hear "The Aquatic Ape Theory" they somehow imagine amphibious frog-people in their mind. This is not what the theory is about. What is supposed by the AAT, is a small community living by the sea or a lake, much like a fishing village, where people fished and collected molluscs for their daily food, used the sea for washing and foraging, and probably even giving birth (another popular human past time that is unheard of in our nearest primate cousins). 

Many people have quite happily accepted the "savannah theory" for the evolution of bipedalism, which stemmed from evidence that during a period of climate change in human evolution, there was an increase in aridity, and consequently, the forest cover that human ancestors likely lived in diminished and probably became isolated into pockets. I don't see quite why early humans then suddenly decided that walking on their hind legs was the fastest way to get from forest pocket to pocket, and especially during the early days of bipedalism, when it would probably have been quite a lugubrious movement and not the fastest form of locomotion (compared to how fast baboons can be on all fours). I think it is not an unreasonable suggestion though, that during warmer, drier conditions, early humans likely sought out bodies of water, whether seas, rivers or lakes, in order to keep cool and hydrated, in the way that many other mammals do, such as elephants during dry seasons, and hippopotamuses (our other mammalian relatives that have lost most of their body hair). It just so happened that humans then decided to set up their base camp near to the water, probably out of convenience because they didn't want to stray too far in the arid conditions. And since they were living by the water, they discovered new food sources, that were rich in omega-3 fatty acids, and subsequently helped them to develop a larger, more intelligent brain. It's not a surprise that the two animals with the highest EQ are aquatic or semi-aquatic mammals with a diet high in omega-3s.
But whilst cetaceans made the move to permanently reside in the seas, early human ancestors merely hung out in is, like hippopotamuses on a hot day, and spent other parts of their day nearby on land. It seems that this was not a permanent change to humanity, and now the majority of human cultures are not dwelling by the sea or freshwater (although many people still love to take their holidays by a beach, given the choice). 
So where is the evidence for this? I hear you ask (or not). Well, unfortunately, the problem with living on the littoral fringe, is that these environments are an archaeological and palaeontological disaster. Beaches and sea fronts are constantly changing with tides, washing away any remains on the shore, rivers can change paths in a matter of years or can dry up due to environmental changes, not to mention the constant change of coastlines due to erosion from wave action. And we haven't even gotten onto changing sea levels yet. As Marc Verhaegen rightly pointed out in his answer "During the glacial periods of the Pleistocene - about 1.8 million to 12,000 years ago, most coasts were about 100 m below the present day sea level" (and this guy should actually know, since he has real human evolution credentials and publications! The Daily Mail should have quoted him instead). This means that all the areas where our human ancestors lived have now long been submerged and likely been washed away and recycled into the circle of nutrients in the sea, or if like some of the brilliant sea bed fossils, chance has allowed their preservation through burial under other layers of soil, we may never see them until millions of years have passed when they may be brought to the surface like the Burgess Shales. The first possible human ancestor (or cousin) fossil recovered from the sea was a piece of Neanderthal bone, and only found in 2009.

Hilarious human evolution cartoon from Abtruse Goose

Next time, rebuttal #2 "Other water-dwelling mammals such as polar bears, seals and hippopotamuses just close their nostrils when they go under water. Why don't humans have the same ability?"

Eat Friendly to Be Friendly

One of the most exciting new studies that I've recently has been that from a group lead by Paul Patterson from Caltech (Cell 155, 1451–1463). Their study has shown that a simple probiotic therapy could improve the symptoms of autistic spectrum disorder (ASD). This study breaks new ground in linking diet and the disorder. Previously, it had been noted that there was a correlation between ASD patients and gastrointestinal disorders such as Inflammatory Bowel Disease (IBD), and there had been some reports of alleviated symptoms through adoption of exclusionary diets such as gluten- or casein-free regimens. Now a new study published in Cell shows could provide some concrete basis through which these diets may have their differing effects on different people. Their results suggests that the state of the gut health in ASD patients is more to do with an imbalance of gut microbiota, rather than specific dietary intolerances 

The group were able to make this discovery after studying mouse models for ASD. One particular type of mouse frequently used is the maternal immune activation (MIA) model, which involves injecting the expectant mothers with a viral mimicking chemical. The immune response from the mothers is thought to affect the development of the embryos and results in offspring that are less social, have increased and anxiety and display more repetitive activity. Crucially, they also seem to display the associated alimentary disturbances such as increased gut wall permeability (“leaky gut”). This means that the intestinal wall is not able to filter all metabolites and biomolecules at the same level as a healthy gut. It can be detected by the increased translocation of certain sugars and also an increase of specific immune factors, such as CLDN 8, 5 and IL-6 in response.

Based on emerging and increasingly compelling evidence that gut microbiota have impacts on personality and social development, affecting a range of emotional issues such as appetite and mate choice, the team investigated further whether there were any differences in the gut commensals between the healthy and ASD mice. After sequencing both sets of organisms, they found the largest difference in the Clostridia and Bacteroides genera.

Since B. fragilis is a common human commensal, Patterson tested the theory whether dietary replacement of this species would have any impact on the MIA mice. In fact, not only did B. fragilis treatment improve ASD behavioural features, resulting in increased social interactions and reduced anxiety and repetitive behaviour, but also ameliorated all the associated gut disturbances and immune responses.

It could be that in certain individuals excluding gluten or casein from their diet happened to tip the equilibrium of gut microbiota back towards a healthy level. However since everyone's commensal bacteria come from a complex range of sources from their environment, this change in diet would affect different individuals to different extents, which may explain the varying efficacy of diet change in ASD. 

Moreover, since ASD diagnoses are constantly on the increase, as well as other diseases with possible auto-immune causes, for example asthma and IBS, it could be that ASD is another result from our increasingly sterile environment. With the recent advances of controversial therapies, such as "helminthic therapy" to treat Crohn's disease, gaining ground, evidence increasingly suggests that keeping entirely disease-free is not a healthy or natural state for humanity, and that attempting to do so has repercussions. The main thrust of the helminthic therapy relies on the fact that helminths release immune-repressing molecules to avoid detection and destruction by the host's immune response. Since modern-day hygiene is relatively recent, this means that the vast majority of humans during evolutionary time were carrying helminths, and thus, the immune response adapted to an equilibrium with their presence. Their sudden removal has meant that the immune response is not kept in check in the same way, and could be going into overdrive, attacking the host's own cells. Moreover, since now we are several generations in to our new, clean world, this could result in mother's having less experienced immune systems, meaning that they are more susceptible to infections during pregnancy, which could result in a similar outcome as the MIA infection model mice. The recent findings that changes in the brain associated with autism could be detected before birth, while the baby was still in the womb, only highlight the importance of the mother's health during pregnancy.

Although further studies are required to create a solid basis of probiotic therapy, the authors note that these findings give hope to a tantalisingly safe, easy and cost-effective treatment for ASD, and possibly other neurological disorders with similar behavioural traits, such as schizophrenia, which has similar anxiety and social impairment problems. It also gives further proof of the importance of the delicate balance between ourselves and our commensals.