Chapter 18: Evolutionary Trends In Hominids

Question 1

• What family are humans apart of? What subfamily? And what tribe?
• Define adaptation
• Explain the evolution of the position of the foramen magnum.
• Explain the evolution of the curvature of the spinal column.
• Explain the evolution of the jaw
• Explain the evolution of the pelvis

Answer 1

• Hominidae -> Homininae -> Hominini
• Any characteristic that helps an organism survive and reproduce in its natural environment.
• Foramen magnum is a hole in the skull of where the spinal cord joins to the brain. Through evolution it’s position moved forward until the skull is able to balance on top of the vertebral column.
• Through evolution, the spinal column evolved into ‘S’ shaped from ‘C’ shaped. The lumbar curve improves body balance in the upright position. The cervical curve enables the head to balance on top of the neck, bringing the vertebral column directly under the centre of gravity of the skull.
• The size and protrusion of the jaw reduced to allow the skull to balance on the top of the spine, as the weight in front of the foramen magnum is approximately equal to the weight behind. Balance is thus achieved with a minimum of muscular effort.
• It became broader and shorter from top to bottom, forming a bowl shape. These changes supports abdominal organs when standing erect. Broader shape also provides more space for attachment of larger glute muscles which move to keep the upper body erect.

Question 2

• Explain the evolution of the carrying angle.
• What is the advantage of being bipedal?
• Explain the evolution of the knee
• Explain the evolution of the foot
• How has the change in centre of gravity assisted humans bipedally?

Answer 2

• Because the pelvis is broader, the hip sockets are further apart so through evolution the femurs converged inwards towards the knees, forming a carrying angle. This ensures weight distribution is close to the central axis of the body and greater stability when walking.
• Increase height of vision, able to carry and pick things up.
• The knee joint is a two-part hinge joint, with one hinge on either side of the ligaments in the middle of the joint. Weight is transmitted to the outer hinge therefore it is larger and stronger than the inner hinge.
• The metatarsals evolved to have 2 arches: a longitudinal arch running from front to back, and a transverse arch running from side to side. The transverse arch is unique to humans which perfected bipedal motion.
• Humans have a larger leg length:body ratio than apes therefore lowering centre of gravity to increase stability when moving bipedally.