(Re)considering the Genus Homo: Reflection on What was Reported in 2017

So it’s less than a month into 2018 and there’s already controversy over a femur. I started writing this post back in 2017…I’m sorry but I just can’t keep up everyone. I really wish I could and I have so much respect for those bloggers that are cranking out responses to all of the <<startling new discoveries that are shaking the foundation of everything we thought we knew about human evolution>>. So mad props y’all.

I say this because 2017 was jam packed with new articles regarding two of the most controversial members of our genus, Homo floresiensis and Homo naledi, and some new dates for the earliest members of our species Homo sapiens. These announcements have been sensationalized in the media (as I attempted to capture above with my statement italicized and bracketed above) so it can be hard to understand what these discoveries actually mean.  Spoiler alert: no foundations shook, just more confirmation that human evolution is complicated! Here’s a very concise summary of the debates/issues as I understand them followed by some of the thoughts I have regarding the most recent findings. Also I’m not going to comment on the Sahelanthropus debate I started off linking to (at least in this post) as that species is clearly not part of the genus Homo but it does serve as good reminder that even the question of who gets to be a hominin can be contentious.

 

The Hobbits

Thanks to some new publications/articles/blog posts in 2017 (like this one or this one or this one) discussion about interpreting the fossil and archaeological record Homo floresiensis was pretty hot. Homo floresiensis captured everyone’s attention when first announced because of their resemblance to Homo erectus (physically and culturally…well depending on who you ask) yet australopith-like size. Quickly dubbed “the Hobbits” because of their small or “dwarf” size, the debate was on as to how to interpret their unique morphology. Most pathological conditions were ruled out and with the recovery of more remains from a second site in 2016 the general consensus seemed to be that they did indeed represent a separate species from all previously recorded ones. The dates for the material culture from the same sites were interesting but seem to be “good” dates; initially the archaeological record indicated that these small hominins were contemporaries of anatomically modern Homo sapiens meaning that oral histories in the region talking about the little people of the forest are supported by these fossils but the lack of fossils providing an overlap means this is debated too.

 

Naledi

So this species seems to have had Kardashian-level publicity even before it was fully recovered and reported. Let me start by saying I think the whole Rising Star Expedition is very cool; I LOVE and RESPECT how open access, public this research project has been and continues to be. I loved following the excavations on social media. I really respect many of the people involved in this project (note I’ve actually never met them but through their public outreach I feel like they are “my” type of people – researchers who are really trying to do good, accessible work), but this also makes it tougher as there are a lot of personalities and public personas involved and the “dark side” of public outreach is that some academics argue it impacts the quality of the work being conducted. So let’s focus on the data because that should be easy especially considering so much is open access right!?

This is where it continues to be tough. The site, while extremely cool (a cave system with a passage called “Superman’s Crawl” – doesn’t get much cooler than that) is very complicated in terms of both recovery of the fossils and of their interpretation. As I tell my students, context is everything. The context of the finds is complicated. The primary researchers doing the excavation and analyses argue that there was intentional, deliberate, disposal of the remains but this is hotly contested.

2017 brought us the announcement of “Neo” (that the nearly complete remains of one individual had been recovered from the assemblage representing at least three individuals) and dates for the finds. The dates are particularly interesting because they are much younger than the morphology of Homo naledi would suggest, and that they overlap with the earliest dates for the members of our species, anatomically modern humans. So we have a really small brained member of our species running around at the same time as us in Africa.

 

Anatomically Modern Humans from Morocco

Up until this article came out, the oldest known anatomically modern human (AMH) remains dated to 180 thousand years ago (or kya) from East Africa, which is supported by genetic evidence that also places the origin of our species to East Africa. Now the oldest specimens of our species are directly dated to 290 kya from a site called Jebel Irhoud. They are associated with lovely stone tools dating to between 280 and 350 kya. So while this does not blow up everything we know about the origins of our species, it does demonstrate that we need to focus on Africa as a continent.

 

Summary Thoughts on the genus Homo

What links these recent discussions on H. naledi and H. floresiensis is that they both challenge what a “late” member of the genus “should” look like. Importantly both have small crania and it has been long held that we should see an increase in cranial size over time leading to us big brained humans. The Moroccan evidence simply requires us to consider a much broader region for our origins.

Now I’m sure someone has remarked this before, and remember I’m not a geneticist, but what if the reason why humans are the only hominins left is because we were the only ones who could successfully interbreed with other hominins? That successfully incorporating and retaining the genes of other hominins into our genome increased our genetic diversity making us better adapted to life on this planet, period. Further what if evidence for interbreeding really is what we are seeing, that shared genes are not simply just remnants of a shared common ancestor?

Genes are a critical piece of the puzzle because as with the new dates and location for the anatomically modern humans, they are suggesting a different origin and one that is slightly later.

As always more data (fossils, dates, etc.) clearly does not mean more answers, just more questions. What is clear to me is that we need to reconsider how we define the genus Homo and how we assign species to this genus. Maybe the genus Homo is the problem; it is honestly poorly defined so I say let us start there. Part of this new definition means that we need to decouple the fossil record from the archaeological record; I know how problematic this sounds (humans are humans because of how we think and behave and this is reflected in our material culture) but direct and clear associations between specific types of material culture and specific species are few AND fail to account for other equally plausible explanations. We assume X species were responsible for Y tools because they are found in the same sites and date to the same time periods but there are so many contemporaneous species why do we continue to insist it’s only the largest brain variants that had the culture. This seems so outdated to me and poorly supported by the very large body of evidence we have. What if some of the variations we see in the so-called tool traditions are because differences in WHO was making them?

As a colleague on twitter posted “I’d love to see a fossil discovery that makes things simpler instead of more complicated” because right now the story of human evolution seems already complicated enough.

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