The common ancestors of African apes--gorillas, chimps,
and humans--evolved a number of changes.
The ancestor of African apes developed a sulcus principalis/frontal-marginal
fissue. Changes in muscular innervation occurred: the median nerve usually
innervates 3 ½ digits, the femoral nerve innervates the psoas minor,
and the flexor digitorum longus is innervated by muscular branches of
tibial nerve. Changes evolved in the clusters of spindle cell pyramidal
neurons: gorillas possess more than orangutans, chimps possess even more,
and humans possess the greatest number.
Ancestral African apes evolved a number of muscular changes. The origin
of flexor pollicis brevis was limited to flexor retinaculum and trapezium,
the flexor digitorum superficialis originated from the intermuscular septum,
the pronator teres was obliquely oriented, the flexor pollicis longus
originated from anterior radius and interosseous membrane, the extensor
digitorum IV sent slips to digits III and V, the origin of coroacobrachialis
occurred on the intermuscular septum, an anterior extension of the coracobrachialis
was usually present, the origin of extensor pollicis brevis came from
the ulna and interosseous membrane, the extensor indicis usually didn't
insert on digit III, the teres minor inserted below the greater tubercle
of the humerus, the origin of subclavius occurred on the first rib only,
the origin of psoas major reached S1, the piriformis usually fused with
gluteus medius, and the insertions of the adductor magnus and quadratus
femoris insertions met. Although the peroneus tertius has frequently been
described as a muscle which only exists in humans as an adaptation to
bipedal locomotion, it occasionally occurs in gorillas and rarely in chimps.
The forearm's deep extensor layer was reduced.
The ancestor of African apes evolved novel characteristics of the spleen
and transverse rugae in the vagina. There was a gradual reduction of the
baculum in higher apes from orangutans to gorillas to chimps to the absence
of a baculum in humans. In apes, three was a reduction in the number of
intromissions/copulation (usually multiple in OW).
The ABCC13 protein contains only 6 exons of the 28 which are present in
the gene due to a frameshift mutation which prevents the other exons from
being translated. The complete protein is expressed in Old World monkeys
while a shared 11 base pair deletion (which results in the frameshift)
exists in humans, chimps, and gorillas. The HLA-Cw*0702 seems to have
arisen before the separation of the higher ape lineages, producing alleles
in humans, chimps, and gorillas.
THE CARDIOVASCULAR SYSTEM
African apes reduced the frequencies of several alternate venous drainage
channels in the skull including occipital-marginal. The palmar metacarpal
artery may be included in origin of radialis indicus, the radial artery
enters the palm at the dorsum of the first interosseous space, the superior
ulnar collateral artery sometimes originates from brachial artery , and
the lateral thoracic artery usually forms an independent branch of axillary