Biology Reference
In-Depth Information
The Anthropoidea, with their relatively large brain size, possess binocular vision
and high visual acuity but a relatively poor olfactory sense. Their high intelli-
gence allows rapid and measured reaction to external stimuli. The extension of
the time periods for gestation, developmental growth and parental care are asso-
ciated with increased powers of learning whilst communication by use of elabo-
rate vocal signals has allowed the development of complex patterns of social
behavior. The menstrual cycle with ovulation has been accompanied by the
development of sexual behavior and signaling in the female. Finally, the omniv-
orous diet of primates may have been responsible for the development of their
characteristic manual dexterity which has allowed them both to explore and
manipulate their environment.
The order Primates contains about 200 living species which are divided into two
suborders: the Prosimii and the Anthropoidea (
Table 2.4
). The Prosimii, which
originated in the Palaeocene (
Figure 2.3
), have retained the insectivoran character-
istics of long face, lateral eyes and small brain. The Anthropoidea comprise the Old
World monkeys, the New World monkeys and the great apes. The New World or
platyrrhine (flat nosed) monkeys are thought to have been isolated since the Eocene
(
Figure 2.3
). The Old World or catarrhine monkeys share a common ancestor in the
late Eocene (
Figure 2.3
) and do not differ markedly in either habits or organization
from the New World monkeys. The great apes include the gibbon and orangutan
from East Asia and the chimpanzee and gorilla from Africa.
2.3.2 Primate phylogeny
The fact that we are able to classify organisms at all in accordance with the
structural characteristics which they present is due to the fact of their being
related by descent.
D.W. Thompson (1917)
The phylogeny of the hominoid primates was initially investigated by means of
DNA-DNA hybridization (Sibley and Ahlquist, 1984, 1987). These studies
employed single copy nuclear DNA to calculate the temperature (T
50
H) in degrees
Celsius at which 50% of all single copy DNA sequences were in the hybrid form
and 50% had dissociated (
Figure 2.4
). The delta T
50
H between chimpanzee and
human is 1.6. Assuming a relationship of delta T
50
H = 1% base mismatches, this
translates into ~3.2 × 10
7
mismatches between the chimpanzee and human
genomes. Sibley and Ahlquist (1987) estimated times of divergence for higher pri-
mates as: Old World monkeys, 25-34 Myrs ago; gibbons, 16.4-23 Myrs ago;
orangutan, 12.2-17 Myrs ago; gorilla, 7.7-11 Myrs ago, chimpanzees-humans,
5.5-7.7 Myrs ago. It is now recognized that the chimpanzee is actually represented
by two distinct species, the common chimpanzee (
Pan troglodytes
) and the pigmy
chimpanzee (
Pan paniscus
) which diverged from each other ~2.3 Myrs ago.
The studies of Sibley and Ahlquist (1984, 1987) received support from Caccone
and Powell (1989). However, the validity of conclusions drawn from DNA-DNA
hybridization data has been challenged and the interpretation of these studies is
still somewhat contentious (Marks
et al
., 1988; Sarich
et al
., 1989; Sibley
et al
.,
1990). Sibley and Ahlquist's scheme is nevertheless in broad agreement with the
fossil record, comparative morphology, immunological studies (Gingerich, 1984)
