Humans as Primates

Objectives Describe primates and their evolution. Describe the major anatomical features that define humans as primates. Outline the trends illustrated by the fossils of early man.

Primate evolution Therapsids were the reptilian ancestors of mammals. Eozotrodon was an early mammal 200 mya. The 3 mammal lines present today Therapsid Eozotrodon, an insectivore

Primate evolution Origin in Asia ~85 mya? Migration to Africa as Pangaea broke up. Millions of years ago

Characteristics of primates As mammals, all species have fur and produce milk. Primates have hands and feet adapted for grasping. They have relatively large brains and short jaws. They have flat nails, not narrow claws. They have well-developed parental care and complex social behavior.

Characteristics of primates The earliest primates were probably tree dwellers. Opposable thumb (toe) for hanging on tree branches. The overlapping (binocular) fields of vision of the two eyes enhance depth perception – an advantage when jumping from branch to branch.

Characteristics of primates Two main groups of primates: Prosimians resemble early tree-dwelling primates. Lemurs of Madagascar and the lorises, pottos, and tarsiers of tropical Africa and southern Asia. Nocturnal species (large eyes, black/white vision). Lemurs - note large eyes (black & white vision)

Characteristics of primates Two main groups of primates: Anthropoids (of human likeness) Monkeys, apes (gibbons, orangutans, gorillas, chimpanzees, and bonobos), & humans. Apes have no tails, unlike monkeys. Day-active (smaller eyes with color vision).

Human evolution Humans & apes share all but the last 5 million years of evolution. Hominoid refers to great apes and humans collectively. Hominid means “man-like” - primate that walks on two feet (no opposable toe). There are 2 main groups of hominids: the australopithecines, which came first and are all extinct, and members of the genus Homo, with all species extinct now except one: H. sapiens.

Human evolution Evolutionary trends Bipedalism vs. arboreal (life in trees). Increased stature: early Australopithecenes were chimp-sized; modern humans are much larger. Cranial capacity: three-fold increase in brain size Dietary specialization: tooth size has shrunk, and incisors are less obvious (not for defense). More parental care: humans are born helpless.

Human evolution Evolutionary trends Bipedalism vs. arboreal (life in trees). Man’s body is centered over the pelvis. Femur attachment altered. Arms are shorter. No knuckle walking

Human evolution Evolutionary trends Bipedalism vs. arboreal (life in trees). Climate change made forests disappear. Weaker “apes” were pushed out of remaining trees. On the ground, humans needed to see over the grass to spot predators (lions) before they saw them. The Serengeti Plain of Africa where humans evolved

Human evolution Evolutionary trends Increased stature: early Australopithecenes were chimp-sized; modern humans are much larger. Chimp Australopithecus Human

Human evolution Evolutionary trends Cranial capacity: a three-fold in- crease in brain size Upright stance narrows birth canal, so a large head can make birthing more difficult. Face is more vertical as time passes.

Human evolution Evolutionary trends Dietary specialization: tooth size has shrunk, and incisors are less obvious (not for defense). Diet switched from plant to cooked animal food. Requires less grinding of food Also, jaw is more V-shaped, less U-shaped

Human evolution Evolutionary trends More parental care: humans are born helpless. Length of care increases with brain size. Humans require care through early teen years.

Physical vs. cultural evolution The human state of consciousness