Final answer:
Apes have high neck muscle attachment to support their heavy skulls and maintain an upright posture. The alterations to the skull and backbone in human evolution have helped humans stand up straight and walk on two legs.
Step-by-step explanation:
Apes have high neck muscle attachment because it helps them support their heavy skulls and maintain an upright posture. The high attachment of the neck muscles allows the head to be positioned directly above the spinal column, reducing the strain on the neck and back muscles. Alterations to the skull and backbone in human evolution, such as the shortened arms, fully upright posture, and decrease in bone mass of the skull and face, have helped humans stand up straight and walk on two legs.