SERMON: “Trimming the Family Tree” by the not-so-reverend bob

Although it’s easy (and correct) to critique religious views that place humanity at the logical end of a creation timeline (whether that creation occurred in the Biblical Garden of Eden or through hundreds of millions of years of evolution), it is worth taking a step back to consider that this teleological bias infests just about every human head, be they believer or scientist.

When (as a boy) I first learned about Neandertals, they were seen (along with every other early hominid) as our direct ancestors.  At that time, all different shapes and sizes of early primates and humans were just sort of crammed into a single family tree, with explanations abounding about how one evolved into the other and, eventually, to us.

Of course, it’s fair to be kind to these ideas (that are now clearly wrong), as we haven’t had all that many ancient human fossils to examine, and the technology to truly examine them scientifically has been developing rapidly over the last forty years.

As my geo-chemist friend pointed out with regards to studying the tectonic actions of Earth “We only have one data point”.  Meaning that we’ve only found one planet (so far) that has the qualities of Earth to study.  When it comes to our early human ancestors, we have a few more “data points” than that but, still, we don’t have all that many.

When a new fossil discovery hits the press, there is always a bold proclamation about how “everything we thought we knew” is thrown out the window, or an equally confident claim of where the fossil fits in our family tree.

But it is a testament to the steady work of science that all such announcements are eventually put through the wringer, and out the other end comes a more sober evaluation of what the new discovery can reliably tell us.

And so the sequencing of Neandertal DNA (quite a story of technology and tenacity in itself) has opened up new swaths of data from bones that we thought had already told us all that they could.

The story of the story we tell of the Neandertals is enlightening.  At first thought to be our classic “caveman” ancestor, brutish and dumb, they have had a sort of re-birth as noble, red-haired, cultured savages who may have been our equals (in their time).  Both of those descriptions are turning out to be a bit overdrawn, and it seems like we are settling down to an understanding that — though necessarily based on frustratingly few pieces of evidence — seems much more likely to be accurate.

In my short monologue "Forbidden Love of the Pleistocene" I tell the story of a doomed love affair between a Cro-Magnon man and a Neandertal Babe. Hey -- it could have happened!

For the Neanderthals now appear to be cousin to our Ice-Age “modern” human ancestors.  It also appears that (though highly evolved in their own right) they may have lacked a handful of key social and cognitive traits that many think made the difference when it came down to a question of “them or us”.

More importantly, it seems to me, we are coming to appreciate them for who and what they were, without the need to either demean or ennoble them out of our own emotional needs to feel guilt or superiority (after all, there is a chance that we played an active role in killing them off about 40,000 years ago).

So what about this “cousin” relationship?  Darwin predicted that it was Africa that was the nursery for modern humans, and he guessed this without a single ancient human fossil to go by.  Subsequent fossil finds (and modern DNA sequencing) have so far proven him right.  There are still some who hold a view that many populations of humans evolved in multiple regions on the planet, but the mainstream view now is one that we did, in fact, evolve in Africa before spreading out into the rest of the Earth.

But here’s where things have gotten interesting.  As always seems to be the case, when scientists first decided that we had, in fact, all “come out of Africa”, they looked for a single migration event that led directly to us.  It seems we can’t help but think that way.  But the science now supports a more nuanced view that, frankly, fits much better with how nature actually works.

Our current view, then, is that there have been lots of lines of humans through the millennium, most of them evolving in Africa, and occasionally migrating out of there where some groups found long-term success (the Neanderthals in the Middle East and Europe, Homo Erectus in China before we “modern” humans arrived).  There are signs in our DNA of a lot of cross-pollination between ancient humans in Africa, which makes sense when we look at other animal populations.  (The fact is that we can’t tell from fossils alone whether our ancestors had spectated to a point where they could no longer exchange genes.  It looks like they hadn’t, despite some surely dramatic morphological and cultural differences.  And, knowing humans as we do, there can’t be much doubt that we would find a way to have sex with just about anything that looked remotely like us).

The DNA evidence also seems to confirm that there was mixing of genes between the Neanderthals and the modern humans that first migrated into their areas (there is no sign of this mixing in modern African populations, nor of modern human DNA in Neanderthals), as well as some mixing going on between modern humans and Homo Erectus in Asia.

What we begin to see is the natural ebb and flow of reproduction among related species in a way that fits with what we observe in other animals.  And here is the key: it has taken us a while to really see ourselves as being “just like” the other animals.  (Even in science, we held on to an idea of our specialness, even when it kept us from properly interpreting the data of our origins).

But having at long last made that intellectual leap, we can now begin to appreciate what we think we know about our evolution.  The picture is complex and rather sobering.  For it turns out that there have, indeed, been countless groups of human varieties since we split off from our last common ancestor with modern apes (but even then, there was much cross-breeding for a very long time!).  If this is true, what happened to all of the other groups of “humans” that did not lead directly to us?  The answer is that they went extinct, in groups large and small.

But not too large, for it appears that the most critical factor in the evolutionary leap that we refer to as the Neolithic Revolution may have had almost everything to do with population size.

Modern studies of hunter-gatherer populations give us a picture of what happens to groups of humans when their numbers drop below a certain threshold: we revert to more primitive means, losing the gains in culture and technology that we achieve when we have more of our fellow humans to exchange ideas (and genes) with.  This, combined with our extended period of childhood (compared to other primates and, it is assumed, other early humans) may be what gave us the advantage over all of the other groups of our “cousins” that managed to hang on to their basic, set ways, for thousands of years but, in the end, could not adapt well (or rapidly) enough to avoid oblivion.

The nice (if we can call it that) thing about this conclusion is that it does make us feel a bit special for being, well, the ones that “won”.  On the other hand, there rests beneath this understanding the uneasy realization that we were incredibly lucky.  For the evidence also suggests that our lineage was down to just a few thousand individuals at times in our history (for more on this look up our “Mitochondrial Eve”).  It also tells us that perhaps Homo Erectus or even the Neanderthal’s might have done equally well had they ever had the right “breaks” that allowed their numbers to expand.

The other stunning part of our story is how we went from being a fairly dispersed species of low population density for pretty much all of our history to numbering in the many billions in an astonishingly short time.  That, somehow, once we got a foothold on our “modern” state of mind (and had developed the social structures and technology to support our increasing numbers) we went from one more smallish troop of naked apes to the dominant life form on the planet.

The “true” story of we modern humans is one of heartbreaking drama, and deeply humbling knowledge.  Entire species of our fellow humans went extinct at different times (the Neanderthals as recently as 38,000 years ago, Homo Florensis — the “Hobbit” — perhaps only 8,000!).  We lost our cousins (or drove them to the brink of extinction) the same as any other modern animal that stands as one of the survivors.

But we couldn’t even come to this picture of the many branches of our human family until we let go of the idea of a single-file, heroic march through time.  Only then could we see the evidence for what it could actually tell us.

This capacity: the courage to see ourselves as we really are, is a huge achievement for us as a species, and perhaps we must give most of the credit to the objectivity of science, and the scientists themselves who have had to fight the same self-centered tendency that is shared by their entire species.

As time goes on, we will continue to discover more fossils.  New technologies (and new knowledge) will wrest more information from those discoveries.  It may well be (it must be, in fact, highly likely) that there will be even more dramatic twists and turns to our human story.  But at least we are now, it seems, ready to hear the truth.

t.n.s.r. bob

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