Chapter 19: Human Ancestors

Question 1

• Briefly describe how the environment could have contributed to the first hominins evolving the free striding gait. How would this gait have increased the chance of survival in that environment?
• Describe the main physical features of the Australopithecine genus in terms of: Skull, Brain, Teeth, Limbs and Vertebral column.
• Distinguish between gracile and robust forms of Australopithecines.

Answer 1

• Free striding gait first evolved in forest environments separated by grasslands. This gait increased chance of survival as the hominins would have needed to come down from trees and cross increasing distances to next group of trees for food and shelter. Being bipedal increased hominin’s range of vision to spot predators and locate food. Hands being free enabled food to be carried.
  1. Skull: low forehead; projecting upper and lower jaw; skull rounded at the back.
  2. Brain: average of 480 cubic cm; more human-like than ape-like.
  3. Teeth: typically hominin being smaller than apes; canines short and non-projecting and together with the incisor form a row of cutting teeth; lack a diastema; teeth in the jaw form a parabolic shape.
  4. Limbs: limb bones suggest bipedalism; pelvic and foot bones typically hominin; non-opposing big toe; thumb shorter and less mobile than later hominins.
  5. Vertebral column: displays curvature typical of hominins; forehead magnum more forward in position than in the apes.
• Robust forms were much bigger in size, 30cm taller and 40kg heavier. They had large, broad molar teeth that contrasted sharply with their smaller canines and incisors. They had powerful chewing muscles that attached a large jaw bone to the skull and, as a result, they possessed massive bony crests on the skull for the attachment of these muscles.

Question 2

• Who was Lucy, and why is she such an important ‘person’ in present theories of hominin evolution?
• Describe the significance of the Laetoli footprints. Why were they such an important discovery?
• Who was homo habilis? What does the available evidence suggest about this fossil hominin?
• What assumptions are made when scientists infer the degree of intelligence from the cranial capacity of a skull?
• Describe the features of Homo erectus that are evident from a study of the skull.
• Neanderthals were once thought to be ancestors of modern humans. What evidence is there that Neanderthals were a separate species that became extinct?

Answer 2

• A 40% complete female Australopithecus afarensis skeleton dated to be 3 million years old, making it the oldest hominin to be discovered. The completeness of the skeleton enabled scientists to determine that she walked upright, strengthening the idea that bipedalism was a unique feature of hominins.
• They were evidence for early hominins walking in a similar way to modern-day humans over 3millions years ago. They give evidence for bipedalism and help determine a date for the evolution of bipedalism.
• A hominin specie that was an adept tool maker. It had a larger brain, smaller teeth, taller and stood more erect than australopithecines.
• Scientist assume that the brain occupies all the spaces in the skull and than an increase in the size of a brain indicates an increase in intelligence.
• A long, low profile; Increased cranial capacity of around 900 cubic cm; protruding jaw, but less so than in H. habilis; thick brow ridges; teeth that were smaller than Homo habilis.
• Using modern molecular evidence, comparison of Neanderthal fossil DNA and modern human DNA, confirmed Neanderthals were a distinct species that existed in Europe during the last ice age.

Question 3

-What 5 features of a Homo erectus skull would enable you to say that it is not an ape skull?

Answer 3

-Large cranial capacity, absence of sagittal crest, more central position of foramen magnum, smaller teeth and less prominent canines.