You’ve heard of Homo naledi, the strange “human ancestor” (really, a cousin) found a while back in South Africa. There were many skeletal remains in a cave, in the kind of shape you’d expect if they had crawled into the cave and died there, not much disturbed. They look enough like other members of our genus, Homo, to be called Homo, but if we assume that increase in brain size is the hallmark of our species, they seem to be an early grade.
Over the last ten years, we have come to appreciate the fact that our genus may have differentiated into multiple species that did not have a large brain after all, and Homo naledi is one of the reasons we think that. And, just as the “Hobbit” of Indonesia (flores) has recently been re-dated to be a bit older than people thought, Homo naledi is now dated to be a bit later than people may have thought.
For me, this is an “I told you so” moment. First, I understand, as do most of my colleagues (but not all), that a regular change over time in a trait in one lineage does not magically cause a parallel change in another lineage (though the co-evolution of a single trait in a similar direction along parallel lineages is certainly possible.) So, there was no reason to require that all later period hominins be like all other later period hominins in those later-emerging traits. Also, since no one has ever adequately explained what the heck our big brains are for, I don’t subscribe to the presumption that all evolution will always evolve the big brain just because our own big brains insist that they are really cool. So, a late small brained hominin in our genus but existing long after the split with us is actually somewhat expected.
Then, there is my sense of age based on the things I’ve seen in the area’s caves.
On another occasion, Ron Clarke, another anthropologist working in the area, showed me the famous “Little Foot” which is a fossil that represents that mummy-to-stone transition, while mostly sitting on the surface of the floor(ish) of a very deep and inaccessible cave. Meanwhile, I’d been working with my friend and colleague Francis Thackeray, and he demonstrated to me how many of the diverse bits and pieces we find of australopithecines are actually probably part of individual skeletons, but discovered and excavated at very different times. These are creatures that got in the cave somehow, and were only somewhat disarticulated after death.
The whole “crawled into the cave” mode of entering the fossil record, and its presumed variant, “fell to one’s death in the cave” is different from the previously presumed process of “leopard kills you, drags you onto a tree branch hanging over a cave entrance and your bones fall into the cave” means of becoming a fossil. It is of course possible, even likely, that both of these processes occurred at various times and places.
Homo naledi, according to Lee Berger, may represent a third way of getting into one of these famous caves. He suggests that the hominins themselves dragged the dead bodies of each other into the caves, as a form of treatment of the dead. That is a spectacularly controversial claim, of course, since with a small brain how can you have a god, and without a god, how can you have ritual or burial? Of course, elephants treat their dead specially sometimes, and their brain is right where it is supposed to be on the famous mouse-to-elephant curve of brain size. And, I’d bet a dozen donuts that even though Homo naledi has a small brain compared to, say, yours or mine, it is probably a good measure above that comparative curve. It was a primate, after all.
The site dates to some time between about 414,000 years ago and 236,000 years ago. That means that the site overlaps with the approximate age of the earliest, probably, modern humans. Here are the details from the abstract of the paper, published this morning:
New ages for flowstone, sediments and fossil bones from the Dinaledi Chamber are presented. We combined optically stimulated luminescence dating of sediments with U-Th and palaeomagnetic analyses of flowstones to establish that all sediments containing Homo naledi fossils can be allocated to a single stratigraphic entity (sub-unit 3b), interpreted to be deposited between 236 ka and 414 ka. This result has been confirmed independently by dating three H. naledi teeth with combined U-series and electron spin resonance (US-ESR) dating. Two dating scenarios for the fossils were tested by varying the assumed levels of 222Rn loss in the encasing sediments: a maximum age scenario provides an average age for the two least altered fossil teeth of 253 +82/–70 ka, whilst a minimum age scenario yields an average age of 200 +70/–61 ka. We consider the maximum age scenario to more closely reflect conditions in the cave, and therefore, the true age of the fossils. By combining the US-ESR maximum age estimate obtained from the teeth, with the U-Th age for the oldest flowstone overlying Homo naledi fossils, we have constrained the depositional age of Homo naledi to a period between 236 ka and 335 ka. These age results demonstrate that a morphologically primitive hominin, Homo naledi, survived into the later parts of the Pleistocene in Africa, and indicate a much younger age for the Homo naledi fossils than have previously been hypothesized based on their morphology.
Since both articles are OpenAccess, you can see them for yourself. Kudos to the authors for publishing in an OpenAccess journal.
And now, back to my original digression. One gets a sense of how landscapes and land forms develop, and while this can be misleading, it is not entirely absurd to postulate rough comparative ages for things you can see based on other things you’ve seen. I had assumed from the way they were described originally that the Rising Star hominins would not be millions of years old. Even though Bigfoot (found by Clarke) was millions of years old and essentially on the surface (of a deeply buried unfilled chamber) I guessed that over a million-year time scale, the Rising Star material would either become diagenetically inviable as fossils or buried in sediment, or both. But over hundreds of thousands of years? That was plausible to me. In fact, I figured the remains to possibly have been even younger, and if a date half the age as suggested was calculated, I would not have been surprised.
The evolution of our thinking about human evolution went through a period when we threw out all of our old conceptions about a gradual ape to human process, replacing that with a linear evolutionary pattern with things happening in what was then a surprising order, with many human traits emerging one at a time long before brains got big. There was some diversity observed then, but the next phase of our thinking involved understanding a dramatic diverstiy of pre Homo (the genus) life forms followed by the essential erasure of variation with the rise of Homo erectus and the like. Over the last decade and a half, we are now realizing that while the later members of our genus probably did cause, or at least, were associated with, a general decrease in that early diversity, later diversity arose anyway, and there were more different kinds of hominids, very different in some cases, late into our history. Word on the street is that we can expect to learn about even more diversity in coming years.
Paul HGM Dirks, Eric M Roberts, Hannah Hilbert-Wolf, Jan D Kramers, John Hawks, Anthony Dosseto, Mathieu Duval, Marina Elliott, Mary Evans, Rainer Grün, John Hellstrom, Andy IR Herries, Renaud Joannes-Boyau, Tebogo V Makhubela, Christa J Placzek, Jessie Robbins, Carl Spandler, Jelle Wiersma, Jon Woodhead, Lee R Berger. 2017. The age of Homo naledi and associated sediments in the Rising Star Cave, South Africa. May 2017. eLife.
Related books:
Almost Human: The Astonishing Tale of Homo naledi and the Discovery That Changed Our Human Story
From Apes to Angels: Essays in Anthropology in Honor of Phillip V. Tobias
, that is now available for pre-order, and that you must read.
,by Donald R. Prothero, is the first extinct animal book that you, dear reader, are going to give to someone for the holidays.
, Chritie Wilcox explains why this is important. We tend to think of the interaction between animals, within or between species — those interactions that have to do with sexual competition, feeding, or predator avoidance — as involving tooth, nail, squiggly appendages, and all that. But these interactions also involve, very often, some sort of envenomation. Also, using venom isn’t always about stinging, paralyzing, or killing. Mosquitos use venom to make blood sucking possible, as the chemicals used to stop their host from feeling the bite, and to make it easier to suck the blood, etc., are venoms. Indeed, the parasites we know to be so commonly associated with mosquitos get into the host by hanging out with the venom, free riding with the injected biochemicals.
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. I’ve looked through that book, and it is nice. But here I’m going to review a somewhat more recent book, just out, by Don Prothero, which has at least as much information in it but by focusing on a smaller number of cases: 
. Either way, you can safely assume the more recent volume is more up to date in areas where research has been active.
by Jonathan Tweet.
is an astonishing book that needs to be on the bookshelf of anyone interested in evolution. The work is edied by Steve Parker, but authored by nearly a dozen experts in various subfields of fossils and evolution, so it is authoritative and scholarly. At the same time, it is very accessible and enjoyable. This is not a book you read from cover to cover, though you could. Feel free to skip around, and you;ll find yourself looking stuff up all the time.
by Michael Gerald and Gloria Gerald is a compendium of biological topics and key moments in the history of biological science, organized in a sort of chronological framework. Major groups (the insects, the amphibians), major ideas (Pliny’s Natural History, Ongogeny and Phylogeny), key physiological and developmental concepts (meiosis, mitosis, many topics in endocrinology), key fossils (like the Coelocanth) and so on are discussed, very nicely illustrated. This is almost like having a gazillian short articles from Natural History Magazine (or similar) all in one book. There are 250 biological “milestones” in all. The charming part of the book is that a milestone can be an evolutionary event, an extinction episode, the emergence of a great idea, or a particular discover. And, as noted, these are ordered across time, as well as one can, from the beginning of life to a selection of the most recent discovery. The book effectively combines history of biology (and related sciences) and the biological history itself.
by the well respected scientist and historian Matthew Cobb is a carefully and clearly written history of the discovery of the nature of DNA, covering a lot more than, and since, Watson and Crick. It is extremely well sourced, indexed, and supported, and very readable.
is a an updated version of a classic book about evolution and extinction written by one of the scientists who developed our modern way of thinking about evolution and extinction (especially the extinction part).
as an expose of a particular time period and major event in geological history. 
by Dean Falk is a great book focusing on one key human fossil. This is a personal story as well as a scientific one. Again, available used for a song.
yet? I’m sure you’ve heard about it. It is still a great read, and you can get it used cheap.
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