This brings me neatly to my final point. In research on disorders such as autism or Williams syndrome, a significant group difference is considered to be the holy grail. In terms of getting the study published, it certainly makes life easier. But there is another way of looking at it. If you find a group difference, you’ve failed to control for whatever it is that has caused the group difference in the first place. A significant effect should really only be the beginning of the story.
Wednesday, June 29, 2011
via Carl Zimmer, Dr. Jon Brock in his blog, "Cracking the enigma," has some thoughts on why null hypotheses don't suck so bad as so many people think. Null hypotheses are generally along the lines of, "there is no difference between these groups," or "this variable has no effect on something," or "there is no relationship between variables." The more general statistical statement behind the null hypothesis is usually along the lines of "this phenomenon can be explained just as well by a completely random process." I'd agree with Brock that it seems that a good many researchers (not me!) view the null hypothesis as a bore or meaningless. But I like his final thought:
Monday, June 27, 2011
A few months ago in a post about the ilium and cannibals, I relayed a quote by Dr. Raymond Dart who was the first to recognize (and name) the hominid genus Australopithecus, back in 1925. I'd also mentioned that he was described [in a reference that escapes me] as "blood-thirsty." This macabre descriptor came to mind again, as I'm reading his (1948) description of the MLD 2 mandible, of a juvenile A. africanus from Makapansgat cave in South Africa (figure is from the paper):
"[Individuals represented by MLD2 and another skull fragment] met their death by manually applied violence. The fractures exhibited by the mandible show that the violence, which probably occurred in fatal combat, was a localized crushing impact received by the face slightly to the left of the midline in the incisor region, and administered presumably by a bludgeon... this youth probably met his fate at the hands of a kinsman more expert than himself in the accurate application of directed implements" (p. 393-394)
This rather fanciful hypothesis may reflect Dart's alleged bloodlust, and the condition of the fossil likely reflects damage that occurred after death during the sometimes abusive process of fossilization.
Dart, R. (1948). The adolescent mandible of Australopithecus prometheus American Journal of Physical Anthropology, 6 (4), 391-412 DOI: 10.1002/ajpa.1330060410
Thursday, June 16, 2011
National Geographic aired a special tonight about a recently-excavated child's skeleton (they focused on the skull) from Grotte des Contrebandiers in Morocco, dated to around 108,000 years ago. So far as I know this material has not been fully published (aside from a brief blurb in Science). Hmm, a highly publicized TV special on a big hominid fossil discovery around/before the scientific publication, sounds familiar...
The program presented work of archaeologists, paleontologists, reconstruction artists, taphonomists, and lots of other people, hoping to figure out who the kid was and such. All in all it was pretty cool, I'd recommend checking it out if you didn't see it. Or again if you did see it.
While I think it was a great program and the researchers involved are doing a terrific job, I had two main concerns: first, I wish they'd treated the topic of growth-n-development a little more. They noted that the child (5-6 years old possibly) looked really "modern" because of its flat face. But looking at it, it didn't really have that flat of a face, especially for a child. They talked about how human-like (rather than Neandertal-like) the kid was, but they only compared it with adults - children tend to have relatively smaller faces and larger brain-cases than adults (right), so it's no wonder it looked more like an adult human than the adult Neandertal from Amud (Israel) that they compared it with. It would've been great to see more comparisons with other late Pleistocene hominid kids, such as from Skhul/Qafzeh or La Quina. A future program, perhaps.
Second, they kept asking whether the kid was "a Homo sapien." I know it's counterintuitive for English-speakers, but "H. sapiens" is the singular and plural of humans' scientific name. Silly, right, cuz it doesn't even get paid twice as much. But you'll have take that up with C. Linnaeus. I am a Homo sapiens. You are a Homo sapiens. Fifty people are a gaggle of Homo sapiens. I fail my students if they say "sapien" when referring to humans. Because it's not very sapient of them.
Anyway it was a cool show. Check it out, dammit!
Figure credit: Fig. 2 from Bogin. 2003. The human pattern of growth and development in paleontological perspective. In Patterns of Growth and Development in the Genus Homo, eds. Thompson JL, Krovitz GE and Nelson AJ. New York: Cambridge University Press: 15-44.
Tuesday, June 14, 2011
Summer is a trying time for me. Many people take the time to relax, do things they couldn't during the academic year. I do that, but I also get really restless. I try to do all that relaxing or different stuff at the same time, which just overwhelms me. I even have a hard time focusing on working on the dissertation (australopithecine growth and development; more on that in future post, promise). The academic year forces upon me a self-discipline whose bonds I break to become a directionless, scatterbrain piece of crap once summer begins. Although, I have been running a ton.
But sometimes I can force myself to focus on a small task for just long enough to be "productive." The other day it was kitchen science. I'm not much of a cook ("add butter" that's my meal-time motto), but thought I'd (re)try my hand at making gazpacho, a summery soup. But as part of my summer attention issues alluded to above, I didn't have the patience to follow a recipe. I decided to exercise my human ability to do things my own way even though I don't know what I'm doing and others before me have already successfully invented the wheel, as it were. I'd made some gazpacho last year based on a recipe, so I figured I'd just try to recall what I did then. I used fancy orange tomatoes last year, and although delicious to eat, it looked something like this (not what it's s'posta look like). This year, my gazpacho debacle would be scientific because I'm testing the null hypothesis that my cavalier approach to cooking will turn out no different than real recipes.
So first we gather up some ingredients: some exotic looking (but bland) peppers (Hungarian or cubanelle), a more banal looking but better tasting orange pepper, tomatos, onion, cucumber, and an avocado for its beloved fat. Rye pale ale is not mixed in with the veggies, but drunk until everything sounds like a good idea. Next, go Lizzie Borden on the veggies until they're all diced up. Puree about half the abomination in a blender and pour the puree into a bowl or pitcher. Dump into the blended glop those diced veggies whom you've spared a cuisinartistic demise. Maybe throw in some spices or something. Then let sit in the fridge for hours. HOURS! Who could wait that long?
The results (to the left) show a few things (the milk on the right is not mine, I only drink half-and-half). First, I reject my null hypothesis, that that my version of gazpacho would be identical (in color and texture) to Ina Garten's. Second, and more interestingly, the mixture looks fairly similar to last year's recipe (which did look like barf), even though I used slightly different sets of ingredients. It is also delicious in spite of its appearance (what's that they say, about judging covers and burning books)? And as a friend once told me, "hey, it all looks the same on the inside [of your stomach]."
I think this second attempt at gazpacho, and my first summer edible experiment, ultimately demonstrates that I should never be allowed to cook for anyone ever again.
If you have any killer summer recipes, feel free to share!
Wednesday, June 8, 2011
One of my favorite paleoanthropological sites is Dmanisi, in the Republic of Georgia. It is the oldest securely dated hominid site outside Africa (just under 1.85 million years ago), and the hominids found there display a neat mix of primitive Homo habilis and derived H. erectus features. I consider myself lucky to have had the opportunity to excavate at Dmanisi last year, and to return to Georgia (lamazi Sakartvelo! [I hope I translated that correctly]) for more fieldwork next month.
Recently, Reid Ferring and others (2011) described the results of excavations of M5, a section of the site a bit aways from the area where the hominids were found. M5 is pretty cool because it presents a nice geological "layer cake," as Ferring described it to us: each of the strata (different layers of deposition) are nicely and evenly stacked on one another. Check out the labeled layers on the right of the figure, from Ferring et al. 2011:
This is in stark contrast to the jumbled strata (like 'spaghetti') where the hominids were found. In geology and archaeology, there is a general "law of superposition," which states that the lowest layers in a sequence would have been deposited earlier than the layers above them. The A sediments at Dmanisi, as seen in the figure above, are thus older than the Bs. Hominids have only been found in the B sediments. But work at M5 has shown that stone tools are found in the older A sediments, meaning that hominids arrived at the site and used it continually, beginning just after 1.85 million years ago.
Tools from the site differ between the older A and slightly later (still older than 1.75 million years!) B sediments in both material and manufacture. As they say in the paper (p. 2/5), a major difference in tool manufacture between the strata A and B occupations could be that during the earlier A times, "either cores were more intensively reduced or selected flakes were made elsewhere and carried to the site." I'm not sure why this may be, but it is neat that within a fairly narrow time span, researchers can see habits change in our early ancestors.
The authors also note that the older tools from A sediments indicate "that Eurasia was probably occupied before Homo erectus appears in the East African fossil record" (from the paper's abstract). If only hominids also came out of the A sediments! The News is touting this as meaning H. erectus evolved in Eurasia and then some members of the 'new species' moved back into Africa, but I don't think this is necessarily the case. The Dmanisi hominids are described as H. erectus, but lack some key H. erectus apomorphies (most notably a large brain size) and really look pretty similar to contemporary hominids in Kenya (such as KNM-ER 3733) and Tanzania (such as OH 16). Plus, the E. African hominid fossil record around 1.9 million years ago leaves some tantalizing hints at hominids more erectus-like than habilis-like, such as the ER 2598 occipital fragment.
So while Dmanisi definitely demonstrates the presence of hominids outside Africa earlier than most well-accepted "Homo erectus" (or "ergaster") fossils in E. Africa, I don't think they necessarily indicate that the species arose in Eurasia. Rather, what the fossil record likely shows is the evolution of populations of early Homo, in Africa and Eurasia, toward the more 'advanced' H. erectus we know and love (due to gene flow w/in a widespread species, rather than parallel evolution of similar traits in different species).
Ferring R, Oms O, Agustí J, Berna F, Nioradze M, Shelia T, Tappen M, Vekua A, Zhvania D, & Lordkipanidze D (2011). Earliest human occupations at Dmanisi (Georgian Caucasus) dated to 1.85-1.78 Ma. Proceedings of the National Academy of Sciences of the United States of America PMID: 21646521