New Roots On The Family Tree

The salient features

Of human-ish creatures,

Our sisters and brothers and cousins,

Across generations

Shows slight variations

And species, it seems, by the dozens

The picture’s still muddy,

As scientists study,

Concerning our relatives’ species

The task is colossal

Inferring from fossils

Of footprints, or bones, teeth, and feces

The clues, though, are leading

To claims of cross breeding

In hominids once thought distinct

With two populations

In different locations

With whom we’re genetically linked

It’s really exciting—

You see, we’re re-writing,

As only hard evidence can,

The view, now outdated

That claimed that we mated

With only the sapiens clan

In NPR's 13.7 blog, Ursula Goodenough writes of recent research on hominid genomes, and the increasingly varied story of our family tree.  To take just one tidbit, it appears that the locals of Papua New Guinea are "roughly 92.5% African, 2.5% Neanderthal, and 5% Denisovan"--that is, this population (with which the rest of us are interfertile, of course) has genetic material belonging to two extinct hominid species, whom we had previously believed were distinct from (read: non-interbreeding with) H. sapiens.  We knew we shared common ancestry with them, but the notion that they are among our direct ancestors (for some modern populations, at least) is new.

As I tell my students, Darwin's Origin of Species was ironically titled, because evolution by natural selection makes obsolete the concept of "species" as it was used at the time (or as creationists still use it).  Rather, as populations vary across time and geography, black and white distinctions simply do not exist.  Take the example of ring species, for instance, where neighboring populations can interbreed just fine, but populations a bit further apart (geographically, or chronologically, it works both ways) cannot, despite a continuous line of interbreeding populations linking the two.  Where is the species line to be drawn?  Are these one species, or two?

Frankly, it's a bit like Pluto.  Pluto is what it is, whether it is called a planet or a planetoid; our linguistic handle on it is for our sake, and simply allows us to talk about it.  The concept of "species" is a similar abstraction; tremendously useful in some cases, impossibly vague in others.  

H. sapiens, H. erectus, Neanderthal, Denisovan, and more... which are "us"?  It depends on the context.  

This, like Pluto, may take some getting used to.  Human exceptionalism (not to mention the historical influence of creationism) and ego ("what a piece of work is man...") have expressed themselves in a history of dehumanizing our ancestors.  Neanderthals are still brutes in the public eye (so easy a caveman could do it), despite recent attempts to update their image.  It would be difficult to maintain our belief that we are the pinnacle of creation, the top of the evolutionary ladder (yes, I know the metaphor is wrong), the final product of nature, if we must also recognize that by some measures we are far more closely related to Neanderthals than we had thought.