Saturday, December 06, 2008

Human variation proportional to distance from Africa?   posted by Razib @ 12/06/2008 02:34:00 AM

Distance from Africa, not climate, explains within-population phenotypic diversity in humans:
The relative importance of ancient demography and climate in determining worldwide patterns of human within-population phenotypic diversity is still open to debate. Several morphometric traits have been argued to be under selection by climatic factors, but it is unclear whether climate affects the global decline in morphological diversity with increasing geographical distance from sub-Saharan Africa. Using a large database of male and female skull measurements, we apply an explicit framework to quantify the relative role of climate and distance from Africa. We show that distance from sub-Saharan Africa is the sole determinant of human within-population phenotypic diversity, while climate plays no role. By selecting the most informative set of traits, it was possible to explain over half of the worldwide variation in phenotypic diversity. These results mirror those previously obtained for genetic markers and show that 'bones and molecules' are in perfect agreement for humans.

The use of skull-traits is a little 1930s...but a trait is a trait. For you anatomy nerds (of which, I am not one), the list of traits is below the fold. And no, cephalic index is not on the list....
1. Maximum cranial length (GOL)
2. Nasion-opisthocranion (NOL)
3. Cranial base length (BNL)
4. Maximum cranial breadth (XCB)
5. Minimum frontal breadth (M9)
6. Maximum frontal breadth (XFB)
7. Biauricular breadth (M11)
8. Biauricular breadth (AUB)
9. Biasterionic breadth (ASB)
10. Basion –bregma height (BBH)
11. Sagittal frontal arc (M26)
12. Sagittal parietal arc (M27)
13. Sagittal occipital arc (M28)
14. Nasion-bregma chord (FRC)
15. Bregma-lambda chord (PAC)
16. Lambda-opisthion chord (OCC)
17. Basion prosthion length (BPL)
18. Breadth between Frontomalare temporale (M43)
19. Bizygomatic breadth (ZYB)
20. Middle facial breadth (M46)
21. Nasion prosthion height (NPH)
22. Interorbital breadth (DKB)
23. Orbital breadth (M51)
24. Orbital breadth (M51a)
25. Orbital height (OBH)
26. Nasal breadth (NLB)
27. Nasal height (NLH)
28. Nasal height (M55)
29. Palate breadth (MAB)
30. Mastoid height (MDH)
31. Mastoid width (MDB)
32. Breadth between Frontomalare orbitale - Frontal chord (M43(1))
33. Frontal subtense (No 43c)
34. Minimum horizontal breadth of the nasalia (sc) - Simotic chord (M57, WNB)
35. Simotic subtense (No 57a, SIS)
36. Breadth between zygomaxillare anterius - Zygomaxillary chord (M46b, ZMB)
37. Zygomaxillary subtense (No 46c, SSS)