Anthropology P380: Lectures 10-12: Early hominid fossil record
Introducing: the fossil record for proto-human diet
If you havn't had an introductory anthro course that covered early hominid fossils, you can refer to my A105 online lecture notes on the early hominid fossil record - they are a little out of date now (written in 1997), but give you a good overview of basics.
We will review the principles behing interpreting key types of evidence that can be derived from fossils:
We now know that, based on genetic evidence, we last shared a common ancestor with chimpanzees between 5 & 7 million years ago -- since that time we have BOTH diverged -- gone our separate ways -- and many think that while chimps, bonobos and gorillas became specialists in eating the soft fruits and herbaceous vegetation typical of the woodlands and forests of Africa, our ancestors became increasingly specialized for making a living in more OPEN habitats ... we've talked a bit about how the distribution and quality of foods can vary between habitats -- both plant and animal foods, and this is a central issue in human origins. Many scientists see the diversification of hominids that took place between 3-1.5 mya as an adaptive radiation -- speciation in response to marked increase in habitat aridity ca 2.8-2.5 mya
.The first fossils that were recognized as proto-humans from Africa were discovered and described in the 20's and 30's -- between the world wars. These were named Australopithecus africanus and A robustus (also called Paranthropus robustus by some anthropologists)- found in cave deposits dating between 3.5 - 1.5 mya from south Africa. At first just thought to be little ones and big ones, but John Robinson developed a DIETARY HYPOTHESIS to explain the difference, which was championed by Raymond Dart as well... this argued there was a separation in ecological niches -- robusts were vegetarians (slow, stupid, lotus-eaters!) and graciles had smaller teeth, were more omnivorous -- mighty hunters, or "Killer Apes"!
Coming just before WWII this pushed all the buttons about human nature as bloodthirsty and cruel (they hadn't seen chimps hunt!) on the one hand and mighty and nobel on the other -- the HUNTING HYPOTHESIS argued that MEAT-EATING and hunting abilities were what distinguished us from apes ... and these ideas have remained popular to this day. You can read about this in the chapters from the book by Matt Cartmill A View to a Death in the Morning is a marvellous review of the cultural/historical context of the Hunting Hypothesis. (Video snippet of Raymond Dart).
The "hunting hypothesis" explanation of why we became human has been theoretically countered by a (feminist) GATHERING HYPOTHESIS, suggesting that the planning skills and technological abilities that led to collecting, carrying and delayed consumption of plant foods played and equally or more important role in course of human evolution than the meat eating.
Similarly, Robert Brain has reanalyzed many of the australopithecine cave deposits from South Africa, asking questions about how these deposits formed... concluded that most of them were accumulations of bones dropped into the cave by carnivores... and that the hominids in the caves were more likely to be prey than predators (e.g. they were "the hunted" not "the hunters")
Since then, discoveries in East Africa have confirmed a trend among the Australopithecines -- (read brief review in Fleagle book and Alan Walker article)
5-4 mya the earliest hominids known Australopithecus ramidus @ 4.4mya in northern Ethiopia -- bipedal??? With small cheek teeth, relatively small incisors, larger canines and thin enamel = dentally much more primitive than australopiths post 4 mya... very chimp like! Another species, Australopithecus anamensis, dates to around 4 million years ago, and is definitely a biped and a good candidate to be an ancestor of the later east African hominids.
4-3 mya well-known Australopithecus afarensis, like "Lucy" in Ethiopia were bipeds with projecting faces like chimps, broad incisors and moderately sized canines, but much larger molars with thick enamel (the living African apes have thin enamel).
3-1.5 mya later australopithecines Paranthropus or Australopithecus robutus and P./A. boisei developed robusticity in both south and east Africa, and became specialized (derived) "chewing machines" .... mega-dont cheek teeth with massive musculature, and anterior dentition much reduced (tiny incisors/canines) ... (see video snippet) but WHAT did they chew?
Recent work by Fred Grine and others on tooth microwear has confirmed a dietary separation between the South African gracile and robust australopithecines... suggesting that the robusts had more grit in their diet (digging tubers with bone and antler digging tools found in the caves?) and/or ate more smaller/harder foods.
However, some bone chemistry work done by Andy Sillen and Julia Lee-Thorp has suggested that the robusts were quite omnivorous -- high on the trophic ladder (strontium and stable isotopes). A recent article in Science (available online) by Mark Sponheimer and Julia Lee-Thorp suggests that A. africanus may also have had omnivorous habits.
2.4-1.9 mya oldest examples of fossils identified asHomo (members of our own genus), distinguished both by relative brain size (derived -- larger than Australopiths) and by retained generalized dentition (more primitive than Paranthropus) -- relatively gracile face & musculature, wide incisors, smaller cheek teeth.
Australopithecus garhi has just been discovered and described from Ethiopia. There's an interesting debate about what the behavior of this australopithecine was like, based on its morphology, and various artifacts found at the same time period. You can read about A. garhi and examine photos in the online article in Science magazine.
Homo habilis first named by L. Leakey, based on teeth at Olduvai, and then often represented by the large-brained KNM-ER 1470 specimen from East Turkana, and often includes the smaller KNM-ER1813 cranium. Some authors prefer to separate 1470 and 1813 into 2 species: Homo rudolfensis (1470) and Homo habilis (1813) because of their dimorphism. Specimens similar to 1813 also found in South Africa. First appears ca 2.4 mya, and smaller specimens continue to be found in sediments 1.5 mya, contemporary with:
Early Homo erectus (sometimes called Homo ergaster ) first appears @ 1.9 mya in Turkana basin -- including the superb WT15,000 "Turkana Boy" skeleton -- and becomes the sole surviving hominid species. Leaves African continent sometime between first appearance (1.9mya) and 1.5... early sites with fossils and artifacts in Soviet Georgia and Java before 1.5 mya. By 1 mya brain size has increased to 1100 cc ... evolving into mid-Pleistocene species with robust crania and brains ca 1200 cc by 600,000 bp.
BRAIN SIZE turns out to be an important dietary variable, because brain tissue is metabolically costly to support... an "expensive tissue" relative to others. Read about Leslie Aiello and Peter Wheeler's hypothesis about the relationship between brain size, diet quality and gut volume in primates, especially hominids.
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Last updated: 8 October, 1999
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