Saturday, January 26, 2013

Who are we? Don't ask our neurons, they're a bunch of idiots. And don't answer with your gut, because your gut isn't even human.

As the philosopher Daniel Dennett likes to remind us, each one of us is made up of trillions and trillions of living organisms (we call them 'cells'), and not a single one of these living things that make us up has any idea who we are, or even cares.

Take a moment to let that sink in.

Now, don't blame the cells for not caring; they are all living organisms and thus have their own metabolism, their own respiration, and their own reproduction to manage.  They don't have the time to worry about the bigger picture.  Nor do they have the mental capacity.  Even neurons--the living organisms that do our thinking for us--are quite dumb, when considered on an individual level.  Even though it is our neurons that allow us to think and learn, no individual neuron can think or learn.  Each one follows very simple rules of behavior: basically if a certain number of its neighbors are firing, they fire too.  That's it.  And yet somehow, out of all those mindless firings of neurons, a mind emerges--a mind that can even write a blog post about the neurons mindlessly making a mind.

Three stupid neurons.

More than human.
It gets even weirder.  A good proportion of the cells that make us up aren't even human!  Before I tell you what percentage, I invite you to take a guess: What percentage of the cells in our body are human cells?  90%? 70%? 50%?  So far, you're way off.  (Are your neurons even firing correctly?  Sheesh.)  Truth is, human cells are the in the minority amongst humans, by a long shot.

Human cells comprise only about 10% of the 100 trillion cells in a human.  10%.  The rest of the cells in our body are mostly bacteria, which generally take up residence in our gut.  Far from being invasive, our bacterial friends are an integral part of our digestive system, breaking down food and passing along the energy and vitamins to us after they're done with them.

Are you the same "you" that you were 10 years ago?
Biologically speaking, not exactly.  The living organisms that make us up generally do not live long enough to see us grow old.  Our body may grown and develop at a steady, slow pace, but that is due to a complex flux of cells dying and new cells being born to take their place (here's a nice NYT article on this).  The skin that covers your entire body--the thing that makes you look like "you" with your dimples and wrinkles and all--is not even the same skin you had two weeks ago.  The stable patterns in our skin, including our fingerprints and dimples and wrinkles and all, are sort of like traffic jams that persist even after all individual the cars that started the jam travel on down the road.

Down another level, they say that most of the atoms and molecules that make up the cells are replaced by other atoms (of the same variety) every year or so.  Since the new atoms are functionally equivalent to the old atoms, we would never know the difference.

So what are we to make of this?
So, if the neurons that make us think are all stupid, and the cells that make us up are dying all the time, how do we think?  How do we persist?

Part of what makes this all so mysterious is that we are so far removed from the microscopic level of the goings-on of our body that we have no sense of how the micro-level goings-on give rise to the macro-patterns of our daily life.  But there are some systems in nature where the levels are not so far removed, and so we can learn something about this mystery by studying them.  I will briefly introduce you to two of them: slime molds, and ant colonies.

Slime molds
The slime mold may be one of the grossest organisms on earth, but it is also one of the most fascinating.  We humans like to think of our life cycle in terms of our whole body, not our cells, but the life cycle of the slime mold doesn't work like that.

The slime mold spends much of its life as a single-celled organism, not unlike an amoeba, generally sliming around.  But there comes a point in the life cycle where tens of thousands of individual cells come together and act like one big organism.  First this aggregate organism looks like a slug, slithering around, eating, sliming, and doing whatever it is slugs like to do.  Then during it's reproductive stage the slime mold self-organizes into a mushroom-like stalk, releasing new spores into the surrounding environment and starting the whole process over again.

Although individual slime mold cells are just about as dumb as our individual neurons, the aggregate of slime mold cells can be pretty darned smart.  For example, they can find their way through a complicated maze to get to food:

Ant colonies
Although ants may be smarter than slime mold cells, they are still pretty dumb.  What I mean by that is that ants follow a very simple algorithm for guiding their behavior, a very simple decision-making procedure based entirely on pheromones.

If, in their walking around, an ant happens to cross paths with another ant, they give each other an antennae high-five and sniff out the pheromones.  There is a pheromone that signal one of a few basic meanings: "I found food" and one for "I'm working on the hive" and another for "there's a threat to the colony".  If they sniff the pheromone for "I found food", then they head in the direction that ant was coming from, repeating the process with other ants, until it ultimately finds the food.  This is not much different than our dumb neurons' algorithm of "if my neighbors are firing, I will too".

Now, despite being made up of dumb ants, an ant colony is pretty darned smart.  For instance, they can solve the complicated problem of allocating the optimal number of ants to various food sources at various distances with varying amounts of food.  (here's a nice TED talk on the emergent intelligence of ant colonies)

Also, ant colonies persist for decades, even though the individual ants generally die after several months or at most a few years.  (The queen is the exception to this rule, she's around for up to 21 years).

So, ant colonies and slime molds each give us insight on how a form of intelligence can emerge from the collective behavior of dumb individuals, much like mindless neurons can collectively make a mind. They also lend insight onto the persistence problem, how we can be around for decades when most of our cells are long dead by then.

The bigger picture.
Now that we've seen there's no real magic to how we can be composed out of a bunch of dumb organisms but still be relatively smart, there are more questions to consider.  Should we feel bad if we scratch our cheek and kill thousands if not millions of living organisms?  Is it possible that individual humans could be part of some larger system that is even smarter than any individual humans?  If so, should that system feel bad if it happens to "scratch it's cheek" and wipe out thousands if not millions of humans?  And what should we call that system?  I propose that we call this hypothetical system "Frank."  Frank, if you're listening, please don't scratch your cheek!!!

Extra goodies:

  • this article also reports on a finding that human cells even forage for food in a pattern similar to other scavengers, including sharks and um, penguins
  • another video of slime mold finding the shortest path to food through a maze 
  • here's a research article on the how ant colonies solve complicated problems with dumb ants