Friday, March 6, 2009

Darwin, Finally
in which DACSIH? finally recognizes the 200th anniversary

I once made the mistake of visiting Alan Lattimore, a good friend from Wire Mommy Alma Mater, when he was living in Baltimore. In the summer.

Now, don’t take offense if you’re a fan of the town; I like the place. But you’ve got to admit, it can be a miserable, humid, hot environ in the summer.

Anyhow, one time of day was nice, and that was in the evenings, when it started to cool down. We could repair to his apartment’s mercifully shaded, cool, brick front porch, lay back, and sip lemonade.

I don’t remember whether our unexpected guests were Saints or Jehova’s Witnesses. But they came walking door-to-door, and in an Antebellum kind of way it seemed only natural for two ex-College Know-it-All Hippies [1] to invite them up to take a load off, drink some lemonade, and shoot the breeze for a while. It soon became obvious that nobody was converting anybody that day — but we had one of those civilized, respectful exchanges of ideas that human beings are supposed to be able to manage but somehow often can’t.

I don’t remember how we got onto the topic of evolution, either. But I do remember the question one of them asked me, and which encapsulates a lot of the confusion over the issue:

“If humans evolved from apes, why aren’t we still evolving?”

The second part was the easy one, if the answer had a bit of an “all of the above” feel to it:

  • evolution is so incredibly slow with a species that takes the better part of 20 years to mature that it’s very hard to see within a human lifespan
  • there’s some reason to suspect that the way our technology allows us to assist each other may be slowing or at least changing the way we evolve

But the first clause of his conditional question carries a mammoth misconception that many even of evolution’s defenders, including the teachers who teach it, consistently get wrong: human beings did not evolve from apes. We and apes each evolved from a common ancestor, which was neither one nor t’other.

That idea takes some getting used to. It’s relatively easy to imagine the common ancestor of a fish and a lizard looking something like a newt or a frog. It’s much more difficult, with the exceptional place we humans hold in our own minds — and, in terms of our impact on our surroundings at least, clearly have — to imagine a more “primitive” ancestor that shared some orangutan characteristics, say, and some human characteristics. It involves, perhaps, breaking through a wall of Mary Douglasist taboo to even think of such a creature, let alone to accept that it would pre-date anything as “primitive” as an orangutan.

The flaw in the above statement is the casual use of the word “primitive,” which in evolutionary terms doesn’t quite mean what we usually take it to mean. In the realm of evolutionary biology, a bacterium and a shark are in many ways every bit as “modern” as a human being. In some ways their forms are more perfect than ours, as they have survived, with remarkably few changes necessary, for 3 to 4 billion and 420 to 450 million years, respectively, to our measly 250,000.

Still, as mistakes go, it may be that regarding humans, evolutionary biologists have been making the biggest one of all — one that they’ve only recently recognized. Enter an article by Erika Check Hayden in the Feb. 12 issue of Nature. [2]

We make much of the fact that humans and chimpanzees, our nearest surviving relatives, share 94 percent of our DNA sequence. The simple explanation for that was that six percent of our genes are so important that they can make the vast difference between a very intelligent but still “natural” animal and the hyper-tool-using-communicating-building-environment-altering phenomenon that H. sapiens has become.

Only, it didn’t turn out to be simple at all.

For one thing, most of the differences lie in what molecular biologists are increasingly embarrassed to have nicknamed “junk DNA.” The majority of the DNA in eukaryotes (organisms with complex cells that include a nucleus to contain the genetic material) tends to consist of sequences that don’t encode genes or anything else of known function. Even the scientists who originally coined the phrase probably knew that it wasn’t going to be accurate — in some ways, it’s an ironic reference to our inability to figure out what much of the genome is doing. We’re pretty sure it ain’t junk; but it isn’t genes or anything we really understand, either.

For another thing, the fact that two DNA sequences are different doesn’t necessarily mean that they act any differently: many of the differences may be essentially meaningless silent mutations.

Finally: a couple of these DNA differences — such as those within FOXP2, associated with human speech, and ASPM and MCPH1, associated with brain size — do fall within genes for proteins associated with important human characteristics. But researchers are increasingly coming to realize that most of the differences that do mean something nevertheless may be acting only marginally. All told, they just don’t capture what makes us human. [3]

You see, we’d left out culture.

As amazing as it seems, human culture has had such a profound effect on our evolutionary path that it has completely redefined what human evolution means.

Consider: about 50,000 years ago, the human race experienced “The Great Leap Forward” — when our technology began to change and improve radically, in an accelerating fashion. Our genetic evolution took a turn soon after: based on current human genetic diversity, our SNPs — one-base changes in the DNA sequence — expanded noticeably about 40,000 years ago.

Now, none of these numbers is etched in stone just yet: but note that the genetic change seems to have come after the cultural explosion, and certainly not well before it.

There’s a similar pattern, if more tightly grouped, around the Neolithic Revolution about 10,000 years ago. Consider the following:

Now, many of those dates wobble compared with each other. And it isn’t clear which do so because we just don’t have them accurately pinned down, and which do because they happened at different times. They didn’t have to have changed all at once to uphold the point we’re discussing: clearly, ’round about 10,000 years ago, everything changed.

Oh, and that 40,000-year estimate of the initial burst of SNP changes in H. sapiens? That’s based on a more-precise calculation of an explosion of 3.9 million SNPs that researchers looked at in modern humans from Europe, Africa, and elsewhere.

Care to guess how many years ago that burst happened? 10,000 years ring a bell?

Again, the DNA changes did not happen before the cultural changes. At most they were simultaneous, and even may have followed — may have been caused — by the technological and cultural changes.

Why? That comes back to my second answer to our Baltimore visitors: technology, culture, how humans interact and adapt their environment to their needs rather than the other way ’round, makes it possible for us to start collecting new traits that would mean a nasty, brutish, and short life as a pre-hunter-gatherer, but which allow for the kind of specialization of abilities and aptitudes that a complex society needs. It also lets us collect a bunch of behaviors that are learned rather than inherent, and maximize our flexibility of lifestyle because someone will teach you what you need to know, so you don’t need to maintain behaviors in your genes.

Note I said “pre-hunter-gatherer” above, because by the time you get to a hunter-gatherer society your technological and cultural levels are already very complex. As an example, once Heather made the observation that a person we knew who was no good with dogs wouldn’t have survived as a hunter-gatherer. I had the perfect counter: not if, along with a lack of ability to empathize and work with dogs, came a knack for chipping out the best flint spearheads. Somebody like that would more than pull his weight in a hunter-gatherer society, because others could do the dog work.

In real life it probably isn’t quite that pat, but clearly the cultural complexity can and probably did drive the genetic diversity. Increasingly, evolutionary biologists are working this insight into their work as a fundamental property of human evolution.

I mentioned above that I would get back to the 14,000- to 17,000-year date for genetically and anatomically distinct dogs. Dogs, that is, that we can be sure were dogs, because their skeletons or DNA were different from those of the wolves that almost certainly started to hang around human settlements for the bonanza of yummy garbage (and the occasional kid). Many folks — my better half is certainly one of them — suspect that dogs that were distinguishable from wolves by their behavior but not their bodies (i.e., a wolf that sleeps with you and doesn’t eat the cave-bear-rugrats) arose much earlier than that.

When? Well, we don’t have a very good answer for that one; we’re not even all that sure when wolves and coyotes split. So the range of estimates for the earliest possible domestication — 15,000 to 140,000 years — is so broad it isn’t of much help to us. But that range does bracket The Great Leap Forward, and that makes me wonder:

Two events? Dogs as hunting partners 70,000 years ago, before The Great Leap, and as pastoral and agricultural partners 15,000 years ago, before the Neolithic Revolution? Could our dogs have helped trigger the cultural changes that in turn directed our evolution?

There’s no doubt we’ve directed our partners’ development in profound ways. Has the relationship been more mutual than we ever thought? Is domestication co-evolution?

I don’t know the answers to those questions. But it’s something to think about, sitting on your porch, sipping lemonade, with your best friend curled up beside.

[1] God help me, one of the South Park characters looked exactly like me.
[2] While normally I start with primary sources, or at least peer-reviewed review articles, this news piece brought together so many important ideas that I’m making it a special case.
[3] Human exceptionalism is a trap, of course. We move from characteristic to characteristic — language, tool use, empathy — desperate to find one that makes us unique. But maybe the old saying about German shepherds is more to the point: “They’re not number one at anything, but they’re number two or three at everything.” Many little differences, none of them unique, adding up to more than their simple sum.
[4] Scientific observations of teaching among primates, orvids, and canids notwithstanding. Not to mention common experience among dog owners with freely interacting packs!


Anonymous said...

I have wondered about this for a long time. The chronology of it all *is* quite compelling.

Another aspect that I find interesting is how un-ape-like we humans began to be at about the time we first associated with canines. We began to hunt in packs, range over open territory and picked up other behaviors that are more typically canine than ape. It would make sense that close association with another species may have also helped us become neotenized and less fearful/reactive at the same time that these features were enhanced in the proto-dog.

As you imply, maybe the non-dog-trainers were less well adapted and got weeded out.

Anonymous said...

Ken, about 10,000 years ago we came out of the last big glaciation. I believe human civilization as we know it was made possible by the unusually stable climate we've enjoyed for the last 10,000 years. I think that's the only thing that made agriculture possible, and agriculture made everything else possible. Agriculture has undoubtedly been tried before, but it couldn't succeed until you had a very-long-term-stable climate.

And, of course, we are now losing that stability due to global warming, which is going to hammer our agriculture and our economy like nothing we've seen since the Black Death, unless we act massively very soon.

mikelod said...

As a person who recently watched Religulous (all with open minds should see this movie)I find this post very interesting. See intelligence and depth in a blog these days is refreshing.

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Ken Chiacchia said...

Mikelod -- thanks.

Barton -- I was careful to say that dogs helped make the Neolithic revolution possible but not that they were the only thing that made it possible.

In fact, the climatological changes may help explain why there was a 40,000-year gap between the two events: The dogs were there, and working with people, but the environment wasn't making agriculture possible.

In turn, I'd argue, once the climate made farming possible, you'd have trouble getting it to work without the dogs -- anybody who's grown a garden in the suburbs or countryside can attest, you eat a lot more of what you grow if you give your dogs the run of the garden.

Recently we visited Meadowcroft, the prehistoric hunting camp in Pennsylvania, where they also have a simulated Native American encampment. Their display garden was a disaster area, because the local fauna had eaten it to pieces. Real Native villagers wouldn't have had that problem: they had dogs.