Eighth Edition
by Harold L. Levin

Chapter 17 - page 1

Human Origins

Introduction

Humans, Homo sapiens, meaning "thinking man" or "intelligent human", appeared during the latter part of the Cenozoic Era, in the Pleistocene Epoch.

Homo sapiens share many characteristics with the other members of the Order Primates, including basic body structure and biochemistry, but humans are quite distinct from the other primates in many important ways, as follows:

1. Larger, more complex brain
2. Stand and walk erect as result of structural modifications to vertebral column, legs and pelvis
3. Flatter face
4. Teeth less robust
5. Greater manual dexterity, leading to ability to manufacture and use sophisticated tools
6. Greater intelligence, leading to language and culture

Order Primates

Primates are a group of placental mammals. They have five digits, which is a primitive, non-specialized characteristic. They have not developed hoofs, horns, antlers, or trunks, unlike some other groups of placental mammals, and so they remain structurally generalized compared with other mammalian groups.

Principle adaptations of the primates include:

1. Progressive enlargement of the brain
2. Shortening and flattening of the face (reduction of snout)
3. Modifications of the hand - opposable thumb
4. Mobility of the forearm, allowing rotation of the ulna and radius, so that the hand can be turned
5. Modifications of the thorax allowing upright posture
6. Forelimbs and hind limbs diverged in form and function
7. Eyes are close-set and positioned toward front of face, allowing binocular stereoscopic vision and the ability to judge distance

These adaptations may have been beneficial to an arboreal (tree-dwelling) existence, or to catching prey.

Types of modern primates:

1. Prosimians - tree shrews, lemurs, lorises, and tarsiers

   1. Tree shrews and lemurs have long snouts and eyes on the sides of the head. Most digits have claws.
   2. Tarsiers have relatively flat face, close-set eyes for stereoscopic vision, and fingers and toes have nails rather than claws.

   
   Lemur. Wild Animal Safari, Pine Mountain, GA. Photo courtesy of Pamela Gore.

2. Anthropoidea - monkeys, apes, and humans

   1. Monkeys

      1. New World monkeys or Ceboidea - not involved in evolution of humans. Includes spider monkey, capuchin, and marmoset. Most are small.
         Prehensile tails.
         Oldest fossils are Oligocene from South America.

      2. Old World monkeys or Cercopithecoidea - Baboons, mandrills, macaques, rhesus monkeys, Barbary ape.
         Nostrils close together and directed downward, as in humans.
         Tail not prehensile.

         
         Olive baboon, Wild Animal Safari, Pine Mountain, GA. Photo courtesy of Pamela Gore.

   2. Hominoidea or anthropoid apes - tail-less primates.
      Includes gibbons, orangutans, chimpanzees, bonobos, gorillas, and humans.
      Modern species evolved from same ancestral stock that produced humans.
      DNA evidence indicates divergence from human line 5-7 million years ago.
      DNA of chimpanzees and humans is 98.4% similar.
      Similarities in the proteins hemoglobin and myoglobin indicate that the chimpanzee is our closest relative.

      1. Hylobatidae - Gibbons - The most primitive branch of the tail-less apes.

      2. Pongidae - Orangutans, chimpanzees, bonobos, and gorillas.

      3. Hominidae - Humans

      
      Left photo= Male gorilla skul1. (Gorilla gorilla)
      Right photo = Comparison of chimpanzee skull (Pan troglodytes) on the left vs. human skull (Homo sapiens). Replicas. Photos courtesy of Pamela Gore.

Classification of Order Primates.

Document created by: Pamela J. W. Gore
Georgia Perimeter College, Clarkston, GA

March 5, 2006