The visual predation theory provides a possible explanation for the origins of primates. This theory suggests that primates evolved from small mammals, who lived in bushes found on the forest floor. These small mammals ate insects that also lived on the forest floor. In order to catch an insect, these small mammals may have used their hands. Therefore, their hands would have to be designed for grasping objects. They would also have to have had the ability to see the insect sitting on a plant, rock or on the ground. A hand with separate fingers and an oppposable thumb would be very helpful to catching insects. Claws would not be necessary, in fact claws could have made it harder to catch and hold an insect. Good vision, especially depth perception would be necessary for the survival of an animal who ate insects. Once these features had developed, it would have been easy for the small mammals to leave the forest floor and move into higher branches. The features developed for insect catching , were preadaptions for climbing on thin branches in the trees. The hand, that was so good at catching insects, would also be good for climbing and holding onto small branches. The depth perception needed to catch the insects would have improved the ability of these animials to jump between branches and climb. These features developed for insect catching allowed early primates to move into the forest canopy and occupy a new niche. Being able to move on small branches would have allowed these animals access to foods that other tree climbing animals may not have been able to reach. The thin branches found on the outside of trees, usually contain a large amount of fruit, but animals that can only walk on top of the branches, such an squirrels, cannot move out onto these branches. If they do, the branch bends under their weight and there is a good possiblity the animal will fall to the ground. Through time, these early primates may have started eating different types of food, living in different parts of the forest, and developing different social systems. The present variations observed among primates today may have started as a result of this adaptive radiation.
Primate evolution has proceeded through several major stages. Around 60 million years ago, lemur and tarsier like primates had developed in many areas throughout the world. By around 30 million years ago, a form of primate that shared characteristics of both monkeys and later apes is found in the fossil record. This is a fossil known as Aegyptopithecus. Another important fossil is Proconsul, a small chimp-like pongid that existed around 16 to 18 million years ago (see picture left). This fossil has been touted as a potential common ancestor for both chimpanzees and man. During the middle Miocene, around 14 million years ago, there was a global climatic shift. World climates became drier and warmer at this time. There are a number of pongid fossils that emerged at this time. One of the best representatives of this group is Sivapithecus (see picture above). This fossil shows marked similarity to the present-day Orangutan. Based on a reconstruction of pongids such as Sivapithecus, it appears that they were all still quadrupedal around 9 million years ago. The Hominids, those primates that walk on two legs habitually appear in the fossil record around 4 million years ago. At present, anthropologists tend to believe that Hominids diverged from a pongid ancestral form between 5 and 7 million years ago. Unfortunately, there are few fossils from this period that are known. Many paleoanthropologists believe that climatic changes around 5.0 million years ago had dramatic affects on fossil ape populations. As forest areas shrank as a result of drier climatic conditions, competition with more numerous monkey species may have led to efforts to adapt to ground environments and ultimately to savannas where bipedality (upright posture) may have had some advantages.
Prosimians
Pongids
Gibbons
New World Monkeys
Old World Monkeys
Primate Anatomy
Locomotion
Reoriented Use of Senses
Larger Primate Brains
Primate Environments
Dentition
Primate Diets
"Social organization"
Primate Evolution
Infant-Mother Bond and Childhood
Diurnal and Nocturnal Behaviors
Dominance and Hierarchies
Human Organization as Bands
One Final Thought
Introductory Page
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