For some people who follow human evolution news, recognizing “species” is really just about whether you’re a lumper or a splitter. Many people assume that the names of species are about ego, not evidence.
But nature presents us with real challenges, which still cause different scientists to approach the past with different assumptions. Let me give some examples.
Just today, I got notification of a new paper by Walter Neves and colleagues, in which they suggest that Australopithecus sediba and Homo naledi are actually South African representatives of Homo habilis. Some people might scoff at this—after all, the Dinaledi fossils are only 236,000–335,000 years old, while the latest-known H. habilisis around 1.6 million. But a young date for some fossils doesn’t bar them from from membership in a species with much older fossil representatives. Identity is tested with morphological evidence, not geological age.
Now, I disagree with the idea that H. naledi is the same species as H. habilis—Neves and colleagues have come to this taxonomic conclusion by neglecting all the morphological evidence showing H. naledi is different from H. habilis. But it’s not so easy to reject the idea that these species might be close relatives. As we pointed out earlier this year, H. naledi might even conceivably be a descendant of H. habilis or Au. sediba. On the other hand, Mana Dembo and colleagues showed last year that H. naledi seems to be closer to modern and archaic H. sapiens than to H. erectus (and much closer than H. habilis). These are stark differences of interpretation, from similar parts of the skeleton.
At the other extreme, this week Jeffrey Schwartz is set to present results of his own examination of the Dinaledi Chamber sample. According to his abstract, all the teeth belong to one species, but some of the skulls represent another—two species in this assemblage, not just one. I haven’t seen the details of this analysis, but I’m pretty sure I disagree with this one, too.
I admit that it would be fatuous to say that ego plays no role in paleoanthropology. Scientists express provocative opinions that will draw attention from the press.
Still, the trouble with taxonomy isn’t just about new fossil discoveries like H. naledi or Au. sediba. We have seen similarly broad and vociferous diversity of opinions in the last few years about H. erectus, Au. deyiremeda, Au. anamensis, H. floresiensis, Denisovans, Neanderthals, H. heidelbergensis, Kenyanthropus platyops, and others. These are species new and old, and the same issues keep arising again and again.
Many people would say that taxonomic debates just reflect basic philosophy about variation—again, lumping versus splitting. But that’s really only one of the dimensions:
- How much variation should a species include? Broadly, all of us recognize that some species are polytypic (as humans are today), but small and fragmentary samples make it very hard to distinguish polytypy from distinct species. There are living polytypic species that include very extensive variation, and living sister species that barely differ from each other, making model selection difficult.
- What kind of data provide evidence of similarity or difference? Some researchers rely mainly on phenetic similarity measures, using geometric morphometrics, principal components or canonical variates approaches. Others examine discrete (or threshold) traits, counting shared derived traits as evidence of similarity and ignoring shared primitive traits. This group was once dominated by cladists, but in recent years Bayesian approaches have become more and more common.
- What temporal or geological information is sufficient to justify pooling fossil specimens into a single sample? Some scientists are willing to assume that fossils from the same 500,000-year period belong to a single population, even if they preserve different parts of the skeleton or minimally overlap. Others draw trees that separate every specimen into its own “operational taxonomic unit”. The concept of a paleodeme is based on lumping specimens by date and geography, an approach that has come more and more into question as the fossil record increases.
Anthropologists may get a bad rap from other biologists for arguing about taxonomy so much, but in reality many areas of taxonomy are undergoing seismic shifts following more widespread application of genetics and phylogeographic analyses.
For example, bovid systematists have been arguing for the last few years about whether to double the number of species they recognize—a debate about living species with abundant morphological samples and genetic data. Meanwhile, living and fossil elephants are on the verge of a complete revision of relationships, based on ancient DNA and the appreciation of deep diversity between forest and savanna African populations. Similar examples are unfolding across mammalian systematics.
Neandertal and Denisovan DNA has shown us that hominins also exchanged genes by introgression, occasionally but recurrently despite hundreds of thousands of years on their own trajectories. Genetic evidence of African “ghost lineages” means other long-lasting Pleistocene populations once existed.
- naledi might potentially be one such lineage. I have no idea what the closest relative of H. naledi will prove to be. Whether it reproduced with human populations or not, it shows that many cherished human features may not have been uniquely derived evolutionary developments.
I can’t help but feel that we are standing at a special moment in the history of paleoanthropology. New data give us the opportunity to make progress on old areas of disagreement about species and phylogeny. We have to start by taking what we now know about the later Pleistocene, and seriously appling these lessons to earlier periods of human evolution. Our assumptions about the past really are changing.
Whatever we choose to call species won’t change their nature. But our assumptions determine the way we frame our future studies, including our attempts to find more fossil evidence. That makes it important to communicate clearly about what these ancient species mean, both with each other and with the public.
Ian Welsh often says things which stimulate my thoughts.
This time he posted a tweet, ‘Some days I don’t see the point of existence.’
This simple line stimulates enormous ramifications in my ‘thinking-o-sphere’.
An inference being some days he DOES see the point ??
Perhaps there is NO point to existence ? Perhaps it’s all a futile meaningless mess, without any purpose at all ? That could be, might be, the ultimate truth.
But then, into that vacuous void, we humans pour all kinds of stuff to provide meaning and construct a point to our existence.
Like having children, an interesting job, enjoyable relations with other humans, doing exciting adventures, learning stuff that is useful or stimulating, fighting, filling the void with innumerable activities that provide satisfaction. Some of these might be considered luxuries, cream on the top of basic daily survival. Some people are probably grateful to get through a day having had a meal and avoided being murdered.
The possibility remains that it’s all in vain, a distraction, a ploy to avoid looking out of the window into infinite vastness, seen as a meaningless void without any point or destination that we can possibly comprehend.
Some people follow that line and arrive at a totally bleak nihilist vision.
Like ants living on the forest floor below Mount Everest don’t have the capacity to comprehend what the forest is or what the mountain and the sky is, they still pursue their activities so that they survive and procreate. They don’t need to be able to answer the questions regarding What it all is, or Why it all is, or What’s the point of being an ant. They just get on with the business of being an ant, until they die, and other new ants replace them.
Most people do not have the capacity or the inclination to confront these kinds of issues for themselves. What happens, if ever curiosity arises, is that they get handed a pre-packaged prepared bundle of ‘answers’ by various vested interests which want to expand and recruit more ‘believers’.
Hence we have zillions of sects, cults, socio-religio-political groups, ancient and more modern organisations, all competing and trying to acquire new followers and adherents, as they strive to promote their agendas, attain or increase their power and influence.
My political position has moved, continues to move. I’m rather uncomfortable about this, because I feel it’s somewhat involuntary, that I am being forced to alter my stance.
When I was educated in basic biology, circa fifty years ago, I believed and trusted what the teachers and textbooks said. But much has been learned since that time.
I trusted what we were told, that there is only one human species, Homo sapiens sapiens, to which all existing humans belong, and therefore, in a sense, we are ‘all the same’. One big extended family.
Well, now we know, or biologists should explain so that we do now know, that there are actually enormous and very significant genetic differences. This idea was taboo, heresy, when I was taught.
I do not believe that science, in this instance biology, should necessarily be the over-riding ultimate determining factor in how we arrive at social and political positions.
As I see it, going back to ancient Greece, politics is the discourse that takes place in the public arena. It can concern ANYTHING. One week, it’s the price of eggs that’s got everyone stirred up and arguing, the next week it’s whether or not to go to war with the neighbouring tribe because of some perceived transgression.
But for educated sophisticated people to ignore or deny information provided by science is a sort of madness, sheer stupidity or willful ignorance. Science is the best way that anyone has ever come up with for arriving at accurate assessments of any given phenomenon. It’s far from perfect, but wild guesses based on inaccurate uninformed prejudice has got to be so much worse.
The idea, which was indoctrinated into me by science teachers, that all humans are ‘the same’, being of the same species, has turned out to be incorrect, wishful thinking or propaganda.
There were multiple species of hominids or hominims which evolved on different parts of the planet, subject to very different environmental demands. This, I believe, is established irrefutable fact, supported by all the known scientific evidence.
Of course, there are plenty of people who will contest and deny that statement, for a variety of reasons. Some want to introduce extra-terrestrial aliens, some want to adhere to some mythical account supported by their religious traditions, or whatever.
A lot hinges upon the theoretical arguments over how the biological category of ‘species’ should be defined. It’s problematic.
In agriculture and wildlife conservation it has long been recognised that it is important to maintain discrete breeds or species of plants and animals, because they each have valuable individual traits which may be vital or useful at some future time.
That’s the utilitarian argument. I’d argue that we have no right to force any organisms into extinction, although that gets tricky when applied to some of the nastiest diseases. In any case, extinction of species is happening, and accelerating, mostly as the direct result of human activity and the human population explosion.
For humans, it’s maybe somewhat analogous to a painter keeping colours separate on the pallet. You can mix them all, and then you end up with a resulting grey goo and it’s irreversible.
We now have voices seriously arguing that all white skinned humans should be forced into extinction.
[This post is rather brief, because of difficulties with my health problems. 221 visitors yesterday, 241 the previous day. No doubt mostly checking to see if I am dead yet, or not. Pleased to report, only half dead ! Some followers will be grateful for the unusual brevity 🙂 ]