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Showing posts with label Tabun. Show all posts
Showing posts with label Tabun. Show all posts

Monday, April 20, 2009

Tabūn Pelvis Reconstruction

News: Weaver and Hublin (2009) virtually reconstructed the Tabūn C1 female Neandertal pelvis using CT scans.

Background: This is the closest we have to a complete female Neandertal pelvis, so a lot of the discussion centers around obstetrics. When a modern human woman gives birth, the infant enters the birth canal facing sideways so that the head will fit through the transversely oval inlet, then turns 90 degrees so it is facing the back so that the head will fit through the AP oval midplane and outlet, and finally turns another 90 degrees after the head passes through the outlet so that the shoulders can also fit through the outlet.

Tabūn conclusions: Neandertal infants (based on Tabūn’s inlet, midplane, and outlet diameters) only required two rotations: the initial turn so the head faces laterally, and the last turn so the shoulders fit through the transversely oval outlet. This means the infant comes out with the head facing sideways and the shoulders facing front (this is also how australopithecines are thought to give birth). This, the authors suggest, means that Neandertals were more primitive than modern humans. Furthermore, the transversely oval birth canal reflects the cold-adapted wide pelvis associated with Neandertals.

Problems:
  1. Methods: There is no sacrum for Tabun. None. It is possible to predict sacral width and thus reconstruct the inlet, but it is improbable for the outlet to be reconstructed accurately without knowing the sacrum’s length, curvature, and orientation.
  2. Sexual dimorphism: They confuse this throughout the paper. First, they female-ize Kebara (a complete male Neandertal pelvis) by assuming that Neandertals were as sexually dimorphic as modern humans. This has been shown to be wrong previously, so it was a dumb assumption. They also find that this is not the case, making me wonder why they bothered with it in the first place. Then, they claim that the difference between Neandertals and modern humans is that Neandertals are like modern males (who have short pubic rami) when really they’re like modern females (who have long pubic rami). See Rosenberg (2007) for more discussion of this.
  3. Cold- and warm-adaptations: They say that Neandertals were cold-adapted because of the wide birth canal, in contrast to warm-adapted modern humans from Africa. First, wide birth canals do not go hand-in-hand with wide pelves. Second, Tabūn lived in the Levant and thus did not need to be cold-adapted. Third, the Busidima female Homo erectus pelvis from Gona is also wide and also not cold-adapted. Fourth, modern humans in Africa evolved a narrow pelvis to be better adapted to the warm environment is based on... uh... KNM-WT 15000? No, wait, that's also a H erectus, and Gona has already shown that they have wide pelves despite their climate. But what else is there to support this long-held idea? Answer: Not much.
Citations:
  • Weaver, TD and JJ Hublin (2009) Neandertal birth canal shape and the evolution of human childbirth. PNAS Early Edition: 1-6.
  • Rosenberg, KR (2007) Neandertal Pelvic Remains From Krapina: Peculiar or Primitive? Periodicum Biologorum 109(4).