Another PNAS study to share with y’all, this time I caught the announcement via ScienceNOW. ScienceNOW says the paper is out today, but I can’t find it. Go figure. So all I got to run with is this news report.
“from the island of Flores is unlikely to be a shrunken or diseased Homo sapiens, as some have argued, and that its ancestry may instead trace back to ancient Homo species in Africa.”
Two weeks ago we read a very flawed article that concluded Homo floresiensis was nothing more than a bunch of endocrine-ly challenged modern humans. There’s been a so much back and forthing on whether or not Homo floresiensis is a unique species that is has become tiresome to even keep up with the arguments. Sometimes it feels like ego is at more at stake here than really figuring out human evolution.
This new study seems to want to simplify things. From the news article,
“The researchers gathered published data on six measurements of skull shape, such as the height of the cranium and the forward jut of the jaw, on 2524 modern humans, 30 ancient hominids of various species, and the hobbit. Statistical analysis showed that the hobbit skull most resembled H. erectus skulls from Africa and Dmanisi, Georgia, dating as far back as 1.7 million years ago. Then, because the skull’s tiny size presumably influences its shape in certain ways, the researchers did a second analysis considering the effects of scale–in effect asking what type of hominid, if shrunk to hobbit size, would best match LB1. In this part of the study, LB1 most resembled African H. habilis, the most primitive and small-brained species of our genus, also dated to about 1.7 million years ago.
“This is particularly exciting because … it suggests that we really do have a hominin lineage that split off from our own as much as 1.7 million years ago, yet persisted up until the time when modern humans started peopling the Americas,” says Gordon.”
To recap on some osteological goodness, the six measurements are as follows:
- Glabella to Opisthocranion, a measurement of the maximum length of the skull. That’s from the front to the back of the skull.
- Basion to Bregma, a measurement of the of the maximum height of the skull. That’s from the base to the very tip top point of the skull.
- Euryon to Euryon, a measurement of the maximum breadth of the skull. That’s from one side to the other side.
- Nasion to Basion, a measurement of the length of the base of the skull.
- Basion to Prosthion, a measurement of the distance between the base of the skull to the tip of the maxilla (upper jaw).
- Biasterionic breadth, a measurement I haven’t heard of but looks like it is the width of the base of the skull.
I’m gathering that the authors took these multiple measurements and did a phylogenetic analysis. I am getting this from what was indicated in the above excerpt, they compared a lot of modern humans, fewer hominids of various species, and the hobbit. I don’t have the article to confirm this methodology, but I can only assume that is what they did to figure out LB1 is similar to Africa and Dmanisi Homo erectus, even H. habilis in some regards, based off of the measurements.
But, if you have read this paper, “Remains of Homo erectus from Bouri, Middle Awash, Ethiopia,” you should know how reconstructing phylogeny with cladistic analysis between early Homo species is hard and rather inconclusive. We know general trends and large scale similarities and differences, but when it gets to nitty gritty things, the paltry calvarial evidence for big differences between the African and Asian fossils make it really difficult to say Asian Homo erectus was that much different from African Homo erectus. Instead, it is much safer to say that Homo erectus existence spanned large time frames. And that even with a 1.2 million year old difference in time, Homo erectus from Africa to Asia was pretty much the same thing.
For that reason, I wonder how LB1 can be like Homo erectus… especially a really old African erectus as indicated in the report? Above, I put a lateral view of LB1 as well as a lateral view of a Dmanisi Homo erectus (D2700), one that the authors say LB1 resembles. Just by eyeballing the differences between the two skulls we can see that D2700 is much longer, and has a big difference in the basion to prosthion length.
If we take into consideration the works of Asfaw et al., there aren’t many differences between African and Asian Homo erectus that can be figured out thru cladistics. And Asian Homo erectus persists in the record into much more recent times. So, why isn’t LB1 related to an Asian Homo erectus? They should be synonymous, no? What is particularly African erectus about LB1?
Furthermore, how can a tiny hominid like LB1, with a brain half the size of Homo erectus and an antiquity of only 18,000 years old, be compared to one of the root species of Homo? Some of the earliest Homo had brain sizes of 900 or so cc. LB1 had a brain size of 440 cc. Big difference here folk. The news article reports that they ‘shrunk’ the proportions of other early Homo skulls down to LB1’s size to compare. Is that even a valid way to compare? The very fact that LB1 is distinct is its size, so scaling down comparative measurements seems flawed because we’re comparing apples to
oranges watermelons here. You can’t just scale down a watermelon down to the size of an apple and begin to start concluding their similar.
I’m not alone scratching my head over this. Christoph Zollikofer, also has some problems with this cladistic approach. He says the six measurements aren’t enough to
“capture the complexities of skull shape, a concern shared by others. In his view, this kind of analysis might cluster together skulls that are actually distinct. Depending on the species included, says Zollikofer, the approach could end up finding similarities between LB1 and chimpanzees.”
I guess we all gotta wait until PNAS puts out this paper.
- Asfaw, B., Gilbert, W.H., Beyene, Y., Hart, W.K., Renne, P.R., WoldeGabriel, G., Vrba, E.S., White, T.D. (2002). Remains of Homo erectus from Bouri, Middle Awash, Ethiopia. Nature, 416(6878), 317-320. DOI: 10.1038/416317a