The common ancestors of chimps and humans evolved
a number of traits.
THE NERVOUS SYSTEM
In ancestor of humans and chimps, the maxillary nerve supplied the subscapularis
and in the foot, digit II was innervated by superficial peroneal.
Tool usage is especially common in chimps: sticks for termites, wad of
chewed leaves to remove water from tree holes, stout sticks to dig up
ant, bee, or termite nests, leafy branches for sandals or gloves, leaf
cushions to protect from thorny branches, bone picks to extract bone marrow,
leaf napkins to clean themselves and infants, leaves to scoop water, natural
objects to carry water, mortar and pestle to smash palm. The use of signs
to communicate in wild has been observed in chimps. After chimps were
taught sign language, it became evident that chimpse could paint representationally.
It can be argued that wild chimp populations possess rudiments of culture
since not all chimp populations have the same practices/tool usage and
that these practices are passed down in each population as a learned behavior.
THE MUSCULAR SYSTEM
The ancestor of humans and chimps developed an origin of extensor digitorum
on antebrachial fascia, an origin of lateral head of triceps from lateral
intermuscular septum, a fusion of the proximal portion of tensor fascia
lata to the gluteus maximus, an origin of the extensor digitorum on crural
fascia, and an origin of the flexor digitorum brevis on the plantar aponeurosis.
The extensor carpi ulnaris sometimes extends to proximal phalanx V, the
teres major and minor share an origin from intermuscular septum, the clavicular
origin of pectoralis major was reduced. The insertion of the abductor
hallucis may include medial cuneiform and there is frequently a coronoid
origin of the flexor digitorum sublimis.
THE CARDIOVASCULAR SYSTEM
There were also modifications of blood vessels. The interosseous artery
arises from common interosseous artery, the superficial palmar artery
passes over thenar muscles, the medial femoral circumflex sometimes originates
from profunda femoris, and the hamstrings receive musclular branches of
profunda femoris artery. Humans and chimps share dorsalis pollicis vesssels.
In male humans and chimps, the scrotum located more postpenially and testes
increase in size.
Some alleles of the HLA-A and HLA-B genes are shared between humans and
chimps and thus arose before the split between their lineages. The polymorphism
of the HLA-DRB locus predates the split of human and chimp ancestors and
gives evidence for multiregional evolution of human evolution. About 135
alleles are known (of which over 90% evolved after the split between human
and chimp ancestors); some alleles offer resistance to malaria.
Not only are the -globin (eta) sequences of chimps and humans more similar
to each other than to the sequence of gorillas (and humans, chimps, and
gorillas are much more similar to each other than any are to orangutans),
there are changes from the ancestral pattern that humans and chimps share:
transitions at positions 1338 and 4473, transversions at positions 560,
5480, and 6971, deletions at positions 1287 and 3054, and one insertion
at position 3272.
Humans and chimps also share a deletion in globin and a 6 base pair deletion
in intergenic DNA between and globin. Human and chimp recognition systems
are clearly similar in that NK receptors of one species can recognize
the MHC proteins of the other.
At functionally important DNA sites, humans and chimp sequences are 99.4%
identical while at less important sites, the homology is 98.4% homologous