Encyclopedia of Evolution.pdf - Online Reading Center

progress, concept of
arboreal primates. Orangutans are the least social of apes.
They forage separately for fruit. Males and females interact
only to mate, and the only social bond among orangutans is
between mother and infants. With males weighing as much
as 350 pounds (about 180 kg), the gorillas are the largest primates.
The three subspecies of gorillas (the mountain gorilla,
and the eastern and western lowland gorillas) live in the rain
forests of central Africa, in small groups that eat plant materials.
In both orangutans and gorillas, males weigh about twice
as much as females, which is characteristic of the harem. On
at least two occasions, gorillas have been observed to use
wooden tools.
The apes commonly called chimpanzees consist of two
species: the true chimpanzees (Pan troglodytes) and the pygmy
chimpanzee or bonobo (Pan paniscus). True chimps range
from dry woodlands to rain forests throughout central Africa;
pygmy chimps live in a small area south of the Congo River.
They eat a wide variety of foods, including leaves, fruits,
seeds, insects, and occasional red meat. They spend part of
their time in trees and part on the ground (bonobos less than
true chimps). Chimps exhibit behaviors that scientists once
thought were found only in humans, such as the use of tools
(although they do not fashion stones into tools) and warfare.
Most of these behaviors were revealed only when researchers
spent long periods of time with chimp societies (see Goodall,
Jane). True chimps are very aggressive, in contrast to bonobos,
who live in small bands and engage in frequent, humanlike
copulation. As primatologist Frans DeWaal says, “The
chimpanzee resolves sexual issues with power; the bonobo
resolves power issues with sex.” Humans share a common
ancestor with chimps and bonobos that lived only about five
million years ago (see DNA [evidence for evolution]).
Primates similar to today’s prosimians evolved shortly
after the Cretaceous extinction that wiped out the dinosaurs
and other large reptiles. Some other highly specialized
orders of mammals, such as bats and whales, also evolved in
the Paleocene epoch of the Cenozoic period (see mammals,
evolution of). When dinosaurs were no longer the dominant
land animals, mammalian evolution exploded in diversity. One
of the earliest primates, Purgatorius, may have evolved before
the end of the Cretaceous. Purgatorius, and the plesiadapiform
primates that evolved during the Paleocene, lived in Europe and
North America (which were still connected at that time). They
resembled shrews. During the ensuing Eocene epoch, adapid
and onomyid primates evolved. It is unclear which of these
groups may have been the ancestors of monkeys and apes. Both
groups of Eocene primates had larger brains, shorter faces, and
a better ability to grasp than Paleocene primates, and they relied
on sight more than smell. The first true monkeys evolved during
the ensuing Oligocene epoch, in the Old World. Oligocene
primates from what is now the Fayyum deposit in Egypt (such
as Proconsul) may represent the first true apes.
Sometime after seven million years ago, perhaps associated
with the spread of drier conditions across Africa, the
human evolutionary lineage (now usually called the hominin
lineage) separated from the chimpanzee lineages. The
earliest distinctive characteristic of the hominins was upright
posture and walking on two legs, although numerous dis-
tinguishing features (such as very large brains, fashioning
stones into tools, use of fire, use of language) arose later in
the hominin line. The earliest known hominins were Orrorin
and Sahelanthropus from west Africa and Australopithecus
primarily from east Africa. Many australopithecines (and
related hominins such as Kenyanthropus) are known from
the period between five million and two million years ago in
east Africa. The embarrassing plenitude of fossil information
reveals a complex bush of hominin lineages, rather than a
clear line of human ancestry. About the only thing regarding
which anthropologists are certain is that the robust australopithecines
(genus Paranthropus) did not lead to modern
humans. From one of the gracile australopithecines, either
known or yet to be discovered, the genus Homo evolved
about two million years ago in east Africa (see Homo Habilis;
Homo ergaster). Today, Homo sapiens is the only
surviving species of hominin.
The fact that humans are primates means that the physiology
of the other primates most nearly resembles that of
humans. It is for this reason that primates, especially monkeys
and (even better) chimps, are favored for medical experimentation.
The fact that monkeys and nonhuman apes have
large brains and complex behavior means that they may also
experience such experimentation as cruelty, more than other
laboratory animals such as mice, rats, and dogs. For both
reasons, medical experimentation upon primates has become
particularly controversial (see animal rights).
Most nonhuman primates survive in remote areas away
from human contact, and a large proportion of them are
endangered. Most primates are endangered from habitat
destruction, but they are also endangered by predation by
humans as “bushmeat” and for traditional medicine. Only a
few hundred mountain gorillas survive, in the Virunga Mountains
of east Africa.
Further Reading
De Waal, Frans B. M. My Family Album: Thirty Years of Primate
Photography. Berkeley: University of California Press, 2003.
Rowe, Noel. The Pictorial Guide to the Living Primates. East Hampton,
N.Y.: Pogonias Press, 1996.
———. “Primate Conservation, Inc.” Available online. URL: http://
www.primate.org. Accessed May 3, 2005.
Seiffert, Erik R. “Basal anthropoids from Egypt and the antiquity of
Africa’s higher primate radiation.” Science 310 (2005): 300–304.
Stewart, Caro-Beth, and Todd R. Disotell. “Primate evolution—in
and out of Africa.” Current Biology 8 (1998): R582–R588.
Walker, Alan, and Pat Shipman. The Ape in the Tree: An Intellectual
and Natural History of Proconsul. Cambridge, Mass.: Harvard
University Press, 2005.
progress, concept of Progress is a concept that evolution
inevitably leads toward humans, or at least toward greater
complexity. In the minds of most people, this concept is
inseparable from evolution. If evolution has occurred, then it
must have started with simple cells and progressed to complex
cells and more complex multicellular organisms over the
course of billions of years. Nobody can deny that early evolutionary
history was dominated by simple organisms, while