Monday, January 21, 2019

Aquatic Apes: Making Human Evolution Even More Controversial!

If you want to start a fight at a bar, try this.

Ask whether or not humans are apes.

As is typical when you ask for a yes or no answer to a complex question, there are arguments for both sides.  Ultimately, it's a semantic argument.  An ape is defined as a tailless, anthropoid primate.  The family Hominidae (aka the "great apes") does include humans (along with orrangutans, gorillas, and chimps).  However, Wikipedia hastens to mention that in "traditional and non-scientific use," the word ape does not include humans, as if the website is scared of offending someone.

Not my website.
My website is ready to offend and appall all 20 of its readers!

I don't blame Wikipedia for its caution.  There are a lot of vicious arguments about humans being (or not being) apes all over the internet, and not just on creationism websites.  Scientific American, Science Daily, paleontologist John Hawks, and a number of contributors to Reddit have all weighed in on the debate.  (Yes, no, no, and yes, respectively.) (My favorite argument is most certainly the one on Reddit, which refers to the a very clever Talk Origins essay on the subject.)

The odd level of offense humans get from being called apes probably hearkens back to religious considerations.  As Scientific American notes, people were late to accept evolutionary theory, because it required admitting we were more related to chimps than we cared to admit.

But once we accept that we are indeed related to apes, a new argument arose.  What kind of apes were we?  When we picture Neandrathals, we picture hairy, upright hominids hunkered in caves in tundra-like landscapes.  Yet we know early humans got their origin in Africa.  This gives rise to conflicting mental images.  Were we plain-striders, or tree-swinging Tarzans?  There are no caves on the savannah yet we all persist in calling Neanderthals "cavemen."  What gives?

I hereby promise not to use any graphics from Geico caveman commercials, nor the movie "Ice Age."
You're welcome.

Today, I'd like to discuss one of my favorite hypotheses about early humans: the highly controversial Aquatic Ape hypothesis.  Arguably, this hypothesis was doomed from the start because of the name, which includes "ape," that tricky little word that sends people into fits when we use it to refer to humans (or our pre-human ancestors, who most definitely were apes under the taxonomical definition).  It's worth stating, before anything else, that this hypothesis has been neither proven nor disproven, and many evolutionary biologists are highly skeptical.  (These include the paleontologist John Hawks, one of the people who weighed in on the are-humans-apes arguments.)  The Aquatic Ape hypothesis got some recent attention thanks to David Attenborough in a 2016 docuseries called The Waterside Ape.

I think it's always worth delving into scientific subjects.  Ultimately, arguing about human evolution is the scientific equivalent of arguing how many angels can dance on the head of a pin.  We don't know and may never know, and that's okay.  Much of the criticism of the Aquatic Ape hypothesis, in fact, comes from the argument that it is not falsifiable.  (The ability to potentially be disproven as a requirement for scientific hypotheses to be taken seriously is attributed to the 20th century scientist Karl Popper.)

This isn't Karl Popper.  
This is Antoine Jérôme Balard, the inventor of poppers, who also discovered bromine.
I just know there's a "bro" joke in there somewhere...

With new methods of dating and extracting information from fossils, we might well someday be able to falsify or refute the Aquatic Ape hypothesis, just as we have other popular models that once appealed to us.  (A great example is the crystal clay hypothesis of abiogenesis, proposed by Graham Cairns-Smith in 1966.  Although Cairns-Smith continues to argue that life began using clay crystal "backbones" to catalyze the formation of RNA, attempts to model this in laboratories have been unsuccessful, and few scientists today believe this model is the likely answer to whence life came.)

The docuseries "Steven Universe" makes some convincing arguments in favor, though.

Until we find a way to prove or disprove hypotheses like the aquatic ape hypothesis or crystal clay abiogenesis, examining a controversial scientific suggestion is a good way to flex our skeptic muscles.  So, much like the aquatic apes of yesteryear, let's dive in!

The aquatic ape hypothesis was first proposed in 1960, the same decade as the crystal clay hypothesis of abiogenesis.  It was a groovy decade.  DNA had only been fully discovered by Watson and Crick in the 1950s, when they were able to model its double-helix structure after a close examination of Rosalind Franklin's lab notebooks.  Around the same time, Hershey and Chase had shown DNA as the genetic material of T2 phage, confirming that DNA was the basis for heritability in living things.

The basis for up to 80% of daytime television.

Knowing what DNA did, and what DNA looked like, opened a million doors for evolutionary scientists, who could now compare DNA from fossils to living creatures and try to construct how those creatures were related.  Prior to this, taxonomy was based solely on observations ("phenetics).  With DNA in the picture, new evolutionary trees based on phylogenetics were constructed; these trees sought to classify animals based on their genetic relationships to one another.

DNA, however, cannot tell us some things.  It cannot, for example, tell us what kind of culture early hominids had, or how it developed.  This is left up to the imaginations of scientists, one of whom, Alister Hardy, challenged the concept of humans as savannah- or forest-dwellers, arguing instead that humans were shore-dwellers, whose reliance on the ocean (or more shallow bodies of water) was a critical factor in our evolution into modern man.

Among the many things that we note separate us from apes are encephalization (big heads), bipedalism, and hairlessness.

So let's talk about aquatic ape theory.  (Elaine Morgan, a Welsh writer and evolutionary anthropologist, already did, in a 2009 TED Talk!)

Reasons this theory makes sense:
  • The lack of fur on humans seems similar to that of other aquatic and semi-aquatic animals.  For example, hippos, whales, et cetera.  Being unburdened by heavy fur would make humans more adapted to swimming.
  • Humans' bipedalism would aid in wading upright through shallow waters.  (Note that having two legs on the savannah makes little sense, since most human predators would be easily able to outpace us on four legs.)
  • Humans have a ton of body fat compared to other mammals.  Other great apes lack the amount of subcutaneous body fat humans have, and what's more, our skin is particularly oily, with sebaceous glands that secrete fatty (ie, hydrophobic) oils.  
  • Human infants demonstrate "swimming" motions when placed in water.  Could this instinctual reflex harken back to a time when we depended on water?
  • Humans have remarkably good control of our breathing, moreso than any other animals, except dolphins and whales.  The ability to hold one's breath and consciously control breathing makes diving a lot easier.
  • Humans just honestly seem to love water.  We're a real splishy-splashy mammal and gravitate toward bodies of water. 

Since the aquatic ape hypothesis hit the scientific community in the 1960s, it's had a few resurgences.  It was defended in 1980 and again in 1985.  People who defend the suggestion often come up with new arguments in favor.  For example, why would humans evolve to sweat if they were roaming the savannah?  This would be an incredibly wasteful and inefficient means of cooling ourselves down; unless humans were hanging out next to bodies of water all the time, sweating would mean unnecessary water loss.

These all seem like good pieces of evidence, until you realize that none of these arguments are actually scientific pieces of evidence at all.  They're merely justifications for the theory.  If you want to see how justifications aren't the same as evidence, consider the satirical Space Ape hypothesis.Real science needs to establish causality, not merely hint at it.  And in fact, all of the above points can easily be disputed using modern-day animals:
  • Lots of semi-aquatic animals do have fur, such as otters, beavers, agoutis, capybara, et cetera.  In fact, in fresh water, fur is useful because it can help insulate the animal swimming against hypothermia.  
  • There are plenty of non-aquatic bipedal animals.  Just look at kangaroos!  What's more, most semi-aquatic animals are not bipedal. 
  • Lemurs, like humans, have sebaceous glands, and are not semi-aquatic, but tree-dwelling.  We are the only two animals that have these glands.  Why?  No one knows.  Although one argument is that sebaceous glands are a way to make sweating more efficient.  Remember, skin oil from sebaceous glands is hydrophobic.  Although it's worth noting that lemurs neither sweat nor pant to cool down; they lick themselves.  Why lemurs evolved to be so at risk of hyperthermia is anyone's guess.
  • As for the fat, it has already been suggested that human fat stores are designed for endurance; humans are really good at walking and running... and on a savannah, we would need that sort of endurance.  Our ability to store fat goes hand-in-hand with our ability to regulate blood sugar, a critical adaptation for hunter-gatherers.
  • Human breath control is a critical adaption for talking.  Our complex speech requires us to be able to disrupt breathing patterns.
  • Lots of animals like splashing.  This doesn't mean they are aquatic.  In fact, most animals tend to cluster near bodies of water, because water is a necessary item to sustain life.  And for many savannah animals, such as elephants and rhinos, hanging around watering holes means access to mud, a substance that can aid cooling on hot days.
Snow monkeys have long been observed to soak in hot springs.

So,  what is the answer?  The answer is, we don't know.  The model of early humans as semi-aquatic apes is based solely on circumstantial evidence, some of which seems strong but also can be applied wontonly to other animals and breaks down when challenged.

Here's a question: if humans are semi-aquatic animals, why don't we, like otters, beavers, capybara, and others, have webbed toes?

New evidence is emerging that seems to dispute the hypothesis, but at this time, it has still not been officially falsified.  So why bother to talk about it at all?

Asking why is a defining human trait.  No other animal does this. Even more than encephelization or bipedalism, existentialism is a uniquely human trait.

Depressed cartoon animals aside.

Exercises in trying to prove or disprove hypotheses are critical to how we go about amassing scientific knowledge.  We humans may or may not have been aquatic apes, once, but what we are now are critical thinkers.  We have the ability to turn over notional, complex ideas critically, to challenge ourselves, and to engage in scientific debate in a reasonable manner using skills built upon research and reasoning.

I can't say where humans went after we left the trees.  It could have been the savannah, or the shore, or space.  Being able to admit to not knowing is perhaps one of the most important skills a person can develop as a scientist.

Not knowing is the other half!

I don't know where we came from, but I know where we are.  We humans have evolved a remarkable ability to ask abstract questions and seek answers using advanced technology.  And asking about the past, even if we never reach a conclusive answer, is one of the best ways to develop ourselves, and our society, as we move into the future.

1 comment:

  1. The space ape analogy is still a bollocks counter. We don't know of space life to draw analogies from in terms of human traits setting them apart from the other apes, e.g. loss of fur and big brain. We see the traits in question in aquatic species on Planet Earth.