Thursday, August 28, 2014

Anatomically Modern Humans Out-competed Neanderthals with a Combination of Weakness and Fat

Z: So, these... these termites, they're... they're, they're... these guys aren't going to put up much of a fight, right? I mean, we're talking about pushovers, right?
Barbatus: Not really, kid. They're five times our size and spit acid from their foreheads.
Z: [panicked] Hey, wait a minute. Let's not get... we're being too hasty here. These guys sound like bruisers. Just how were you figuring on beating them.
Barbatus: Superior numbers, kid. Overwhelm their defenses, and kill their queen.

             --Antz, 1998

It seems like every article I read about why Anatomically Modern Humans (AMH) out-competed Neanderthals (I like the "h" spelling, and I'm sticking with it) focuses on what short-comings Neanderthals might have had that explains their extinction.  I think that this focus is backwards.  While it may seem counter-intuitive, I think it was AMH's short-comings that led to them out-competing Neanderthals.  To glibly sum up my pet hypothesis, humans wiped out the Neanderthals by being weak and flabby.

Natural Selection is not the same as Survival of the Fittest


People tend to assume that the biggest and the strongest are most likely to survive.  That idea is so strong that it is commonly held as an unquestioned assumption.  In fact the phrase "survival of the fittest" is commonly confused with evolution.  Darwin never used the phrase "survival of the fittest," Darwin's phrase was "natural selection."  Survival of the fittest was coined by Herbert Spencer, and actually expresses a common misconception about evolution.  Evolution does not favor those who are strongest or smartest.  Evolution favors those who make the most babies that in turn make the most babies.

Hypothetically: if you had a type of mouse that lived for 30 years and were smarter and stronger, but didn't start having babies until age three and only had one baby at a time and another group of mice who only lived to three, but had large litters starting at six months, which group would you think were at an evolutionary advantage?  If you went with survival of the fittest you might expect the smart long lived mice to do better, but in reality it would be the stupid mice that make lots of babies early and often that would be likely to be more successful.  Because even though the smart long-lived mice are individually fitter, there are going to be fewer of them.

There are a lot of mice in the world.  They don't live long, but they make lots of babies.  That's a good thing since there are lots of things that eat mice.  If mice took years to reach sexual maturity there wouldn't be enough surviving to keep the species going.

This is just my pet hypothesis, not a commonly accepted theory


Now, just as a heads-up, this is my personal hypothesis.  I have never read this hypothesis in any reputable science publications, so if you are in an archaeology class I would not suggest putting this forward as an accepted theory.  I didn't even come up with this idea through ideas presented in archaeology papers.  My pet hypothesis was inspired by this documentary, The World's Strongest Toddler.  I recommend watching the documentary, it's pretty interesting, but I will summarize.

Myostatin and the World's Strongest Toddler


The World's Strongest Toddler is Liam Hoekstra, who was profiled as a toddler.  He was very unusual because he has a myostatin deficiency.  Myostatin inhibits muscle growth.  That might seem like a bad thing, but here's a picture of a bully-whippet (a whippet with a myostatin deficiency) next to a normal whippet:


When you look at this difference you can see that there could potentially be some problems.  The most obvious for a dog owner is how much food the bully whippet would clearly need to stay so bulky.  That is an important thing to remember going forward.

But all that extra muscle does more than just increase food requirements.  Those big muscles also make it much harder to store fat.  In the case of Liam Hoekstra, he was a toddler with no body fat.  Children need either body fat or constant food.  Because Liam had no fat stores he has much less wiggle room when it comes to skipping meals.  In modern day US that is not too much of a problem, because we have plenty of food.  However, for our evolutionary ancestors there were not fast-food burger joints on every corner.

But Liam Hoekstra is not just stronger and leaner than normal kids, he is also faster and has better balance.  In terms of physicality, Liam Hoekstra is better than you (unless you are the German kid with the myostatin knock-out mutation).  Neanderthals were much the same.

Neanderthals:  Bigger, Faster, Stronger, Extinct


When you think of Neanderthals you might think of the old fashioned representations of them.  Stooped, hairy, and ape-like.  These days the reconstructions tend to look a little different.  Here are some of my favorites:
This was a reconstruction of a Neanderthal woman published by National Geographic in 2008.  The article this was from actually provided a lot of the information that led me to my hypothesis.

A Neanderthal Family reconstruction by the incomparable Atelier Daynes  I strongly recommend you check out her stuff.  She does beautiful work.

And of course, the obligatory Neanderthal in a Suit.
 I show these images mostly to get you thinking about Neanderthals as people.  Because Neanderthals were
people.  People so much like you and me that unless you are of purely Sub-Saharan African ancestry a portion of your DNA is probably derived from Neanderthal ancestors.  Neanderthals were not dumb animals.  They used complex and varied tools, they took care of each other and the old, and they buried their dead.

They also had bigger brains than early AMH on average.  Some people claim that their brains were different somehow and that is why we out competed them.  Personally I find this idea a bit of a stretch.  If we had a good handle on how our own brains actually worked then I might be a little more credulous.  I think that an important thing to remember is that there is a broad range of normal brain sizes for modern humans, and it is not necessarily correlated with intelligence, I think that it is foolish to put too much importance on raw brain size.  But we should also remember that Neanderthals were more massive than humans.  We can compare that to men and women.  Women's brains average about 15% smaller than men's brains, but men's bodies average about 20% larger, which means that men's brains average about two percentage points smaller as a percentage of total body.  But this is kind of a tangent, but let us assume that Neanderthals were roughly as intelligent as humans.

The biggest difference between Neanderthals and humans is their metabolism.  Most humans can get by just fine on 2,000 Calories a day.  An average female Neanderthal probably required more than twice that.  In 2008, National Geographic stated the caloric requirements of an average Neanderthal woman would be 4,034 Calories per day.  That article is actually available online here.  The article was written a few years before the genome studies that found that a small percentage of the modern human genome is derived from Neanderthals for non-Africans.  The article uses the older mitochondrial DNA studies to suggest that Neanderthals were a separate species.  It's kind of ironic, even though archaeology studies things long gone and buried, archaeology is constantly changing.  You might think that the study of static objects from the past would be a static field, but it is not.

Neanderthals were much stronger than we are.  It's not just a matter of muscle size, it is also muscle placement and skeleton.  While it is true that your average neanderthal had muscle mass like a steroidal body-builder, they also had thicker stronger bones and their muscles were placed to provide better leverage.  If you think back to Liam Hoekstra you can remember that his increased musculature makes him faster, stronger, and gives him better balance, and that is on a human frame.  Imagine a group of people that were actually designed to be that strong.

Before moving on let us review briefly.  Neanderthals had slightly bigger brains.  They were stronger.  They had more muscle mass, and heavier bones.  And most importantly to my idea, they had twice the caloric requirements that we do.

Big Brains, Big Muscles, Big Appetites


Those muscles and brains have a very concrete cost.  They require a lot of food.  But not just any food will do.  Our muscles need protein, and our brains need fat.  If you don't get enough protein you can suffer from a type of starvation called Kwashiorkor.  Kwashiorkor is a funny name for a horrible disease.  It would seem to me that if you required much more protein just to survive that it would be much easier to slip into protein wasting.

It shouldn't be too surprising that Neanderthals subsisted primarily on meat.  Recent studies have shown that Neanderthals did eat plants, but the majority of their diet was meat.  Some studies of residue on Neanderthal teeth has shown that they even ate medicinal plants.  Neanderthals understood their world, and ate vegetables and made medicine.  But they mostly ate meat, and their bodies needed that meat.

But we don't just need protein, we also need fat.  There is another silly sounding type of starvation, Rabbit-Starvation.  Rabbit starvation is what happens when you live off of lean meat.  If you don't have enough fat in your diet (or enough carbs to make up the slack) you will starve.  You can eat twelve rabbits a day and starve if you don't have access to fats and/or carbs.  So for Neanderthals with their primarily carnivorous diet, they needed not just meat, but high quality fatty meat.

Those big brains that Neanderthals had needed fat to keep operating needed fat to maintain.  But if they had metabolisms like Liam Hoekstra's then it must have been difficult to keep on a surplus of fat.  They needed fatty meat.  They needed a lot of it.  They needed big game.  And they did hunt big game.

Picky Carnivores vs. Generalist Ominivores


(Now we are getting into my conjectures, this is how I imagine things)

Neanderthals lived on the landscape like predators.  Large predators don't live in high density.  Think of wolf packs or lion prides.  Their groups can't get too big or too dense or there won't be enough high quality prey to go around.  Neanderthals lived in smaller groups than humans, usually in the 5-10 people range.  That size worked for the life style they led.

AMH lived in larger groups, even early humans lived in groups of 20-30.  Humans aren't carnivores.  We eat everything, and can survive on just about anything.  We will selectively eat big game, but if it's not there we can do just fine on grass seeds.  Today most humans live primarily on grass seeds in the forms of staples like wheat, rice, and corn.  With our lower metabolisms and our talent for making fat out of anything we can live in much higher densities.

Our higher population densities also provide us with another advantage, social ratcheting.  When you have a larger group of people you can divide labor.  Neanderthal women and men did a lot of the same work.  Everybody had to be able to do everything because there weren't enough people to have anyone specialize.  Having larger groups also means that there is a higher chance of having old people around.  Old people might not seem like a huge deal, but they are.  If you come across the worst winter in 50 years it can be awfully handy to have someone around who remembers how they survived the last time there was a disaster.

A lot has been made of the years about how slowly Neanderthals changed their technologies.  I think they changed slowly because they didn't have as many people around.  When everybody has to be going all the time it is harder to come up with new ideas.  But that is just conjecture.

I also think that part of the reason that Neanderthals stuck with hand-held spears instead of throwing spears was because they didn't feel the same need that humans do.  Neanderthals were already strong and fast.  They didn't need to find was to stay away from the animals they were trying to kill.  But once again, that is just an idea of mine.

Neanderthals needed the most nutritious animals around in order to survive.  When humans showed up on the scene they probably hunted the same animals.  When the populations of high quality prey dropped it was no big deal for humans, we just ate something else.  For Neanderthals that would have been a disaster.  If the big game was gone from an area they would need to go after it or they would starve.  Even if there was plenty of food around for humans to thrive in higher population densities than Neanderthals ever achieved it still wouldn't be enough for the Neanderthals.

There is evidence that humans and neanderthals fought.  I don't think it was war that wiped out the Neanderthals, but it is a fun thought experiment to imagine what the conflict could look like.  Neanderthals were stronger and faster, but humans didn't need to get up close to kill, they used projectiles.  But even if Neanderthals killed three humans for every Neanderthal, they would still lose, because there are lots of humans.

Conclusion


So there you go.  We don't need to look for any shortcomings in the Neanderthals to figure out why they died off.  We don't need them to be stupid, or unable to talk.  We just need them to be what their biology made them.  Their well designed bodies, highly adapted to the ice-age, were poorly adapted to being overrun by people who needed less.

Neanderthals thrived in Europe for far longer than humans have been around.  They were very successful.  If it all just came down to survival of the fittest one would expect them to still be around.  But other than remnant DNA they are gone and we are here.  We won the evolutionary competition because we are weak and fat.

You could say the weak inherited the Earth.

3 comments:

  1. Very interesting theory and I can't find any reason to rule it out , overall .

    I've often tried to project what humans might survive on a sustainable basis , following various global catastrophes that are well accepted as possible scientifically . I don't think that sheer numbers necessary equate to increased probability of long term survival in these "bottle-neck " events .

    I suspect in some scenarios , that maybe some of the last few "primitive " subsistence cultures may have the best chance .

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    1. If there is one thing that seems to hold pretty true in the archaeological record, it is that people are pretty good at surviving. Generally speaking I think the groups that will have the easiest time of it are those that a living closest to, or under, the carrying capacity of their environment. But depending on the disaster, that capacity would change.

      For example, if it was simply a social/political/economic collapse, then while a lot of people might die in cities in the short term, people in farming areas would probably be mostly fine. An archaeological example of this would be the Mayans. After the end of the Classical Mayan period with all the big city temple building, the population spread out over the landscape, and it looks like the overall population didn't actually change that much, even though the city couldn't be supported anymore.

      In the case of resource over-exploitation, what we could thing of as ecological collapse that isn't necessarily from climate change, it is likely that populations would not change much at all, people's lives would just be crappier. Take Easter Island for example. Most of the traditional archaeological stories about the island were that the ecological collapse led to warfare and population collapse. In this version of things, Easter Island was the only Polynesian Island/Indigenous group of the Western Hemisphere to not be decimated by introduced disease, even though there is abundant material and historical evidence showing that the Easter Islanders were in fact decimated by disease. More recent work seems to indicate that after the trees were all gone people just got used to dealing with less, and eating a lot more rat (and there is evidence of cannibalism). The moral here, is that if our population grows too large, and we destroy the environment, we won't all die. We might just end up eating a lot of rat, carp, and other people... Kind of a Soylent Green future.

      Then of course there is also the specter of climate change triggered collapse. If the climate changes, then even people like the !Kung might have a hard time surviving if the foods that they eat die off. And most of our foods that we farm are temperate climate plants that are evolved for a climate similar to the one we have now. On a geological scale, we are actually still in an ice age. There have been prior epochs that were much warmer than now. The entirety of anatomically modern human existence has been during cool periods, but it is not until the climate warmed up to a more temperate climate that humanity really took off with farming. So who knows what would happen if the earth got significantly warmer. Would we flourish, or would we have such a hard time growing food that populations would collapse.

      It's hard to know, but fun to think about.

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    2. Yes , Jon, people who love people and rats , carp , cockroaches and whatever the can get -Nom ! Nom! Nom! -ARE the luckiest people left in the world !

      I tend to think about worst case scenarios that are just a c-hair short of global mass extinctiion events . Good stuff like super volcanoes (e.g. Yellowstone) or CME solar flares that fry the electrical grid or any number of other well recognized low frequency , high impact natural phenomena .

      I see modern technological civilization as very vulnerable .

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