The common ancestors of higher apes--orangutans, gorillas,
chimps, and humans--evolved a number of new features.
THE NERVOUS SYSTEM
Higher apes increased the volume of limbic nuclei, which were subsequently
increased again in humans. Cerebral asymetries are known in fossil hominids
and apes including a longer left sylvian fissure. The cerebral asymmetries
of higher apes and fossil hominids are similar to those found in modern
humans. Higher apes developed a sulcus frontalis inferior and the gyrus
postcentralis was separated from the parietal lobe. The ACC of non-apes
lack clusters of spindle cell pyramidal neurons. Orangutans possess some
THE MUSCULAR SYSTEM
The ancestor of higher apes underwent a number of muscular changes. The
extensor indicis usually didn't insert on digit IV and the rectus femoris
developed 2 heads (variable in all but humans). Higher apes developed
an articularis genus and an extensor pollicis brevis. The latissimus dorsi
developed an additional origin on the iliac crest.
In the great apes, the sphenosquamosal suture may divide the foramen ovale.
In robust australopithecines the smooth floor of nasal cavity resembled
that of modern humans. This condition is also known in orangutans and
about a third of chimps.
Higher apes share changes in eta globin: 3 deletions (positions 164, 966-70,
1,610-1,637), an insertion (245-82), and at least 24 substitutions (positions
5, 66, 383, 405, 495, 573, 780, 853, 926, 1268, 1278, 1334, 1422, 1667,
1859, 1949, 2002, 2093, 2137, 2138, 2161, 2188, 2193, and 2213). Higher
apes also share 7 amino acid residues in red opsin and 9 in green opsin
which are unique to higher apes compared to Old World monkeys (Deeb, 1994;
gibbons not in analysis). Proteins of the electron transport chain have
experienced positive selection in the lineage leading to higher apes (such
as COX4-1, COX7AH, COX8L, and ISP). Zinc Finger Proteins 75A, 75B (a pseudogene),
and 75C are highly conserved in humans, chimps, gorillas, and orangutans.