Between the skull and the sacrum, humans have 24 vertebrae. Well, most humans, anyway. Sometimes humans have a few more or less.
Humans vary in the length of the lumbar region, the number of vertebrae between the lowest ribs and the pelvis. The typical number is five, but some people have only four. Rarely, people have six lumbar vertebrae.
Non-human primates also vary in the number of lumbar vertebrae. This variation is connected to locomotion. Species with vertical, suspensory postures have relatively short lumbar columns. Chimpanzees, gorillas and orangutans have fewer lumbar vertebrae than humans. Quadrupedal primates, including most monkeys and prosimians, have longer lumbar columns than humans.
What to do: This station has several skeletons of different kinds of primates — both New World and Old World monkeys and apes. Determine the number of lumbar vertebrae in each of these primates. Do these primates vary in the other segments? Do they ,for instance, have the same number of ribs?
- Consider the number of lumbar vertebrae in gorillas and orangutans. Explain how these apes each have relatively few lumbar vertebrae and humans have more than either. What do you suppose was the number of vertebrae in the common ancestors of these apes and humans?
- Why do quadrupeds have a longer lumber spine?
- Why do you think there is very little variation in the cervical spine?