What Changed as Apes Became Humans

Challenges to clear

• Match all seven trends.
• Connect the change in the forelimbs to what it freed our ancestors to do.

The task

Each ape-like condition on the left became a human condition on the right. Match the pairs.

What this lesson covers

• Body covered with hair, as in Australopithecus — Hair on the limbs and body highly reduced (Reduction in body hair is one of the major changes listed for the move from an ape-like form to the human form. Table 14.2 shows it thinning at every stage.)
• Cranial capacity of 450 to 600 cm³ — Cranial capacity of 1450 to 1600 cm³ with a much enlarged cerebrum (Increase in cranial capacity is the headline trend: 450 to 600 in Australopithecus, 680 to 735 in Homo habilis, 800 to 1125 in Homo erectus, about 1450 in the Neanderthals and 1450 to 1600 in modern man.)
• Low forehead with eyebrow ridges projecting over the eyes — Steep forehead with reduced brow ridges and a flattened face (The brow ridge shrinks and the forehead rises as the front of the braincase expands. Cro-Magnon already had a broad arched forehead with only moderate brow ridges.)
• Lack of chin and a prognathous, protruding face — Prominent, well developed chin with the snout gone (Development of the chin is a listed change. Australopithecus, Homo habilis, Homo erectus and the Neanderthals all had almost no chin; the well developed chin appears with Cro-Magnon.)
• About 120 cm tall, walking nearly straight — Up to 190 cm tall and entirely erect, with four reversed curves in the spine (Height and posture improve together: 120 cm and nearly upright, then a bent-kneed 150 cm, a stooping 160 cm Neanderthal, a fully erect 180 cm Cro-Magnon and finally modern man.)
• Forelimbs put on the ground, walking on all four limbs — Bipedal locomotion, with the forelimbs freed from the ground (When forests dwindled because of glaciation the common ancestors came down from the trees and walked on all fours. Bipedalism and the freeing of the forelimbs is the first of the major changes.)
• Large canines and heavy jaw power — Small canines and reduced jaw power, teeth set closer together (Reduction in the size of the canines follows from omnivorous feeding habits, and loss of jaw power goes with it.)

Hint

Read Table 14.2 across the rows rather than down the columns. Every trend runs one way: cranial capacity up, brow ridges down, chin forward, body hair down, height up, canines smaller, posture more erect.