Introduction
A. Approximately 70 million years ago, no primate populations existed in the world.
B. Perhaps about 65 million years ago, some ancestral rodent-like
populations began to undergo new selection pressures. Through the process of speciation, primates began to appear.
C. The original “push factor” in this series of speciation events is highly debated, but a likely candidate is the need to hunt tree living, fast-moving insects for food.
What Is a Primate?
Biological anthropologists, however, define primates on the basis of behavioral, adaptive, or evolutionary tendencies. The eminent British
anatomist Sir Wilfrid E. Le Gros Clark (1895–1971) identified three prominent tendencies:
1. Primates are adapted to life in the trees—they express arboreal adaptation in a set of behaviors and anatomical characteristics that is unique among mammals.
2. Primates eat a wide variety of foods—they express dietary plasticity.
3. Primates invest a lot of time and care in few offspring—they express parental investment.
Why study primates?
• Primates are physically and behaviorally similar to humans in numerous ways. For example, forward-facing eyes and grasping hands in both groups indicate a common ancestry.
• Primates, including humans, are remarkably diverse, yet they all show ability to adapt to a wide range of circumstances.
• Owing to biological similarities between primates and humans, the study of diseases in primates helps us understand and cure diseases in humans.
• Primate diversity reflects the diversity of animal species. Reduction in primate diversity is a barometer of the “health” of the animal kingdom.
Arboreal Adaptation
Primates have a versatile skeletal structure: Primates have a
generalized skeletal structure. The bones that make up the shoulders, upper limbs, lower limbs, and other major joints such as the hands and
feet are separate, giving primates a great deal of flexibility when moving in trees.
Primates have an enhanced sense of touch: Primates have an
enhanced sense of touch. This sensitivity is due in part to the presence of dermal ridges (fingerprints and toe prints) on the inside surfaces of the hands and feet. The potto, a prosimian, has primitive dermal
ridges, whereas the human, a higher primate, has more derived ridges, which provide better gripping ability.
Primates have an enhanced sense of vision: Primates have an
enhanced sense of vision. Evolution has given primates better vision, including increased depth perception and seeing in color. The eyes’
convergence provides significant overlap in the visual fields and thus greater sense of depth.
Primates have a reduced reliance on senses of smell and hearing:
Primates have a reduced sense of smell. The smaller and less
projecting snouts of most primates indicate their decreased reliance on smell.
Dietary Plasticity
Primates have retained primitive characteristics in their teeth: One fundamental anatomical feature in primates that reflects their high degree of dietary diversity is the retention of primitive dental
characteristics, especially of four functionally distinctive tooth types:
incisors, canines, premolars, and molars. The mammalian ancestors of primates had these same tooth types and so must have eaten a range of foods.
Primates have a reduced number of teeth: While most primates have at least one tooth of each type, primates have reduced the total
number of teeth in their mouth – a process known as dental reduction.
The primitive mammalian dental formula is 3.1.4.3, which means that each quadrant of the mouth contained three incisors, one canine, four premolars and three molars. Living primates have lost at least one incisor and one premolar in each of the four mouth quadrants.
Primates have evolved different dental specializations and functional emphases: primate teeth tend to be less specialized than those of other mammals. Primates are omnivores, being capable of eating a variety of food items. Primate teeth are comparatively generalized and designed for processing a diversity of foods.
Parental Investment
Fertility: Birth to relatively few offspring at a time, commonly just one.
Birth interval: Relatively long period between births.
Preadult care: Elongated and intensive preadult care.
Monkey or Ape? Differences Matter
Differences between monkeys and apes track different evolutionary histories.
CHARACTERISTIC MONKEY APE
Body size Generally smaller Generally larger Posture/locomotion Generally horizontal
body trunk Relatively vertical body trunk
Body trunk Narrow Broad
Tail Has a tail Lacks a tail
Lower molars Bilophodont lower molar
(cercopithecoids only)
Y-5 molar pattern
Brain Relatively small Relatively large
Growth Relatively fast Relatively slow
Interspecies variability High Low
CONCEPT
