Primate Evolution
Primate History:
The first primates were small arboreal mammals. Their dental structure suggests that they descended from insectivores in the late Cretaceous. Purgatorius unio, found in Montana, is considered to be the oldest primate. Primates have been around for 65 million years (end of the Mesozoic Era). As tree dwellers they possess characteristics that separate them from the rest of their community. They include: Limber shoulder joints, dexterous hands for hanging on branches and holding food, sensitive fingers with nails not claws, stereoscopic vision, excellent eye hand coordination, and single births with extensive post natal care.
Modern Primates:
The primates of today are divided into 2 suborders: Prosimmi (pre monkeys) and Anthropoidae (monkeys, apes, and humans). The Prosimmians ( lemurs, lorises, pottos, and tarsiers) probably resemble the early primates, but there is a question as to which of these is ancestral to the modern primates. Two groups of prosimian fossils are recognized by paleontologists. One ancestral to the tarsiers, the other to the lemurs, lorises, and pottos. These two groups split about 50 million years ago casting doubt as to which group was ancestor to modern primates. Recently a new fossil discovery has raised a third possibility. Fossils found in Asia and Africa, which date back at least 50 million years appear to be more similar to the anthropoids than either group of prosimian fossils. These fossils indicate an early splitting from the prosimians and their link with the anthropoids. Fossils evidence indicates that anthropoids were established in Africa and Asia about 40 million years ago. Ancestors of New World monkeys may have reached North and South America by rafting from Africa. New World and Old World monkeys evolved along separate pathways. There are four genera of apes: Hylobates (gibbons), Pongo (orangutans), Gorilla (gorillas), and Pan (chimpanzees). Apes are confined to the tropical regions of the world. They are larger than monkeys with long arms and no tail. Apes have larger brains than monkeys allowing them to exhibit more adaptable behavior.
Human History:
The science of human origins is called paleoanthropology. Since its conception there have been many erroneous theories proposed because of individuals working in isolation and a lack of sufficient evidence. There are many misconceptions dealing with how man originated. One being that our ancestors were chimpanzees or other modern apes. Our ancestors were not chimpanzees or any other modern ape since humans and apes represent two divergent branches of the anthropoid lineage which evolved from a common, less specialized ancestor. A second misconception is that humans evolved in an orderly series of steps from an ancestral anthropoid to Homo sapiens. The current thinking suggests Human evolution contains a number of dead ends with several different species of humans coexisting at the same time. A third misconception is that various human characteristics evolved in unison. Mosaic evolution occurred with different features evolving at different times. For example some ancestral forms may have walked upright but had small brains.
  • Early Anthropoids: The oldest known fossils of apes are of Aegyptopithecus, the "dawn ape," which was a cat size tree-dweller about 35 million years ago. About 25 million years ago decedents of the first apes diversified and spread into Eurasia. Around 20 million years ago the climate of Africa and Asia became drier and their forests began to recede. Many areas of anthropoids were isolated from each other and evolved separately. Most anthropologists believe that humans and apes split from a common African anthropoid ancestor 6-8 million years ago. Evidence from fossil record and DNA support this conclusion.
  • The First Humans: Australopithecus africanus was discovered by Raymond Dart in 1924. This early human walked full upright, and had human teeth and hands. Its brain was about 1/3 the size of modern humans. This species appeared about 4.4 million years ago and lasted for over 3 million years. A closely related fossil of this species was that of "Lucy". "Lucy"(A. afarensis) is about 3.18 million years old. The skeleton was over 40% complete and measured a bit over one meter in length. Another fossil discovery, not far from where "Lucy" was discovered were different that a new humanoid species was named, A ramidus. To date, this latest find is considered the oldest know hominid.
  • Homo habilis: Fossils of this first species of Homo showed evidence of a larger brain, measuring about 650 cc. Simple stone tools were also found at times with these large brained fossils. These organisms lived in Africa about 2.5 million years ago. Both the Homo habilis and the Australopithecus lived at the same time, with H. habilis giving rise to the first Homo erectus.
  • Homo erectus: was the first hominid to leave Africa into Asia and Europe. Fossils of Java Man and Piking Man are examples of this group of humans. This species of man lives from about 1.8 million to 300,000 years ago. These individuals had a larger brain 1200 cc. and were taller than the H. habilis. They lived in huts or caves, built fires and refined stone tools . Their descendants Homo Neanderthal lived in Europe, the Middle East and Asia from 135,000 to 30,000 years ago.
  • Modern Man: Homo sapiens : There are two models of how modern humans developed and populated the earth: The Multi regional Model and the Mono genesis Model. The multi regional model suggests that Neanderthal and other post-Homo erectus hominoids were ancestors to modern humans and that modern humans evolved along the same lines in different parts of the world. The mono genesis model suggests Homo erectus was the ancestor to the modern human who evolved in Africa and migrated all over displacing other humans living at the time. Modern molecular techniques are being used to examine the question of human origin. The comparison of mitochondrial DNA from multiethnic groups has traced all humans to Africa beginning about 200,000 years ago. Other evidence using DNA has been uncovered to support the mono genesis model. Humans from below the Sahara show a greater genetic diversity than those of the rest of the world. Based on the founder effect and genetic drift this would seem possible since those entering a new environment would have less diversification due to a shrinking gene pool.