Lumbar Vertebrae - Evolutionary Variation

Evolutionary Variation

Extant African apes have three and four lumbar vertebrae (Bonobos have different spines with an additional vertebra) and modern humans normally five. This difference, and because the lumbar spines of Nacholapithecus (a Miocene hominoid with six lumbar vertebrae and no tail) are similar to those of early Australopithecus and early Homo, it can be assumed that the Chimpanzee-human last common ancestor (PHLCA) also had a long axial column with a long lumbar region, and that the reduction in the number of lumbar vertebrae occurred independently in each ape clade. The limited number of lumbar vertebrae in chimpanzees and gorillas result in an inability to lordose their lumbar spines, in contrast to the spines of Old World monkeys and Nacholapithecus and Proconsul, which suggests that the PHLCA was not "short-backed" as previously believed.