Why do you think the foramen magnum is positioned near rear of cranium for knuckle-walking species and center bipedal species?

Knuckle-walking species

In knuckle-walking species, the foramen magnum is positioned near the rear of the cranium to facilitate a more horizontal orientation of the head and spine. This positioning allows these species to maintain balance and keep their heads stable while moving quadrupedally on their knuckles. By having the foramen magnum located further back, the weight of the head is evenly distributed, reducing the strain on the neck muscles and providing better stability during locomotion.

Examples of knuckle-walking species include chimpanzees, gorillas, and orangutans.

Bipedal species:

In contrast, bipedal species such as humans have the foramen magnum positioned more centrally in the cranium. This shift in the foramen magnum's position allows for an upright posture with the head balanced on top of the spine. The central positioning of the foramen magnum enables humans to maintain an erect posture, freeing the forelimbs for various activities and allowing for efficient bipedal locomotion.

By having the foramen magnum located closer to the center of the skull, the head's weight is distributed more evenly over the spine, reducing the muscular effort required to hold the head upright.

The distinct positioning of the foramen magnum in knuckle-walking and bipedal species reflects the adaptations that have evolved in response to their respective modes of locomotion and body orientations.