And out of the ground the Lord God formed every beast of the field and every fowl of the air and brought them unto Adam to see what he would name them, and whatsoever Adam called every living creature, that was the name thereof.
By naming something, we imply that we know something about its true nature, and we claim ownership of it. For many, this is the seductive elixir that motivates the taxonomic naming of biological organisms. The rules for naming are therefore not only a hook to hang your newly named organism on, they also provide a structure that variant of each organism from getting its own name. The naming of organisms needs to fit into our current understanding of evolutionary relationships in the tree of life, and is based on the principle of parsimony. That is, the simpler the better.
Still, there will always be so many somethings to name (most estimates suggest that we have described about 10% of living species, not to mention the extinct ones that inform the evolutionary tree) – so much variation in form, function, and behavior. The central job of the taxonomist is then deciding how much of that variation reflects differences within a species, or differences between species. Sometimes a single discovery has the potential to tip that balance, turning many species into one variable species.
A new understanding of our evolutionary history
Experience is simply the name we give our mistakes.
An important new archaeological discovery from Dmanisi, Georgia in western Asia was published in Science last month by Lordkipanidze and others, and illustrates this point. The site is dated to about 1.8 MYA and had previously revealed four important skulls of early Homo erectus, the earliest evidence of this human ancestor outside of Africa. The new discovery of skull #5, clearly a contemporary of skulls #1-4, extends the range of at least one important trait, cranial capacity, for H. erectus. Cranial capacity is correlated with brain size and therefore cognitive ability, and the near doubling of cranial capacity (from < 700 cm3 to > 1200 cm3) over ~ 1.5 million years of evolution in H. erectus is considered a strong evolutionary link to early humans. Importantly, skull #5 is below that range at 546 cm3, which suggests that cranial capacity of H. erectus overlaps that of other paleospecies of Homo (H. ergaster, H. rudolfensis, H. habilis), effectively blurring the lines between them. Finally, the variation among the 5 skulls at Dmanisi, though great, is on par with the range of variation seen in modern chimpanzees and humans.
There is no principle worth the name if it is not wholly good.
– Mahatma Ghandi
Like I said, so much variation. Where are the species in this? Well, according to Lordkipanidze and others, the most parsimonious explanation for this big mess of overlapping variation is that several paleospecies of Homo are actually a single evolving lineage that gave rise to Homo sapiens, and its proper name is Homo erectus. Goodbye, H. rudolfensis? Are Rudolf’s feelings going to be hurt? (Probably not, it is named after a lake in Kenya).
The lesson(s) for all biology
What’s in a name? That which we call a rose by any other name would smell as sweet.
The lessons for those who study macroevolution is obvious – the fossil record only provides a slice of the variation in morphology and development stages that once existed, and a single discovery can blow our current understanding out of the water. But evolution informs all of biology (I’ve already reached my quote-quota, otherwise I’d cite Theodosius Dobzhansky here) This discovery is a reminder that a species is just biological variation circumscribed – it never will be a representation of immutable form. This applies just as much to all species alive today, and we would be wise to expect phenotypic variation in all contemporary species. In fact, it is the genetic variation behind the traits we can see that natural selection acts upon, and the reason biological organism evolve!
There is a still broader lesson for all biologists. The hypothesis of multiple species, contemporary with H. erectus, was valid before this discovery and still is. All scientific hypotheses are as valid as the data that support them, but must be falsifiable, and new data may always come to light that refute them. Be prepared to have your perception of the natural world disrupted, and be prepared to view that disruption critically and objectively.
All my life, my heart has yearned for a thing I cannot name.
– Andre Breton