History of Primates

In 1859, Darwin published The Origin of the Species, which has become the basis for the modern day theory of evolution. From his studies, particularly those he conducted in the Galopagos Islands, Darwin was convinced that animal species are mutable or capable of change. At the time, it was already known that:

Darwin was responsible for hypothesizing that:

These are the basic premises of Darwin's theory of evolution. He believed that this explained the diverse array of species that exist today. He concluded that fossil remains of extinct species were evidence of a continuum of characteristics shared with modern day (extant) species. His theory also provides an explanation for the resemblance among the various species of primates, particularly the Great Apes. Darwin posited that humans were a twig on the tree of primate evolution, sharing a common ancestor with chimpanzees. Both fossil evidence and studies of living primates have offered us insight as to how primates might have evolved into a distinct Order of mammals.

Several biological adaptations have made it possible for primates to inhabit diverse ecological areas. An example of an extremely significant adaptation in primate species is the development of prehensile hands and feet capable of fine and precise motor control. Thus primates can easily move food from hand-to-mouth, and perform gymnastic locomotor behaviors such as leaping and jumping from branch to branch among tall trees. Adaptations of the mammalian skeleton included a clavicle, or collar bone, for increased movement in the shoulder; two separated bones in the arms and legs (ulna and radius and tibia and fibula); five digit hands and feet; one or more nails instead of claws; sensitive touch pads on hands and feet; and fewer kinds of teeth for obtaining and processing food. Primates developed with an increased emphasis on vision thus overlapping, or stereoscopic, color vision became more important as a means of gathering information from the environment . Therefore, eyes are located on the front of primate skulls. These biological changes were necessary for the development of depth perception of arboreal dwellers and their quick movement through tall trees and dense vegetation. The emphasis on vision means that the importance of smell was reduced. The diminished dependence on smell was reflected in the reduced snout of primates.

In time, the ratio of the primate brain grew larger in relation to body size and more complex behavior resulted from the addition of neurological tissue. Primate behavior became increasingly more complex, enabling them to live in larger social groups and inhabit a greater range of ecological niches. The complexity of primate behavior is an important factor in the success and proliferation of primate species to other continents.

Primates are heavily dependant on learned behavior. Information must be learned and shared through social groups composed of infants, children, and adults. All stages of growth and development, as well as adulthood were lengthened to accommodate the acquisition and passage of information from one generation to the next generation. Complex social behaviors are learned from play, trial-and-error, problem solving and observational learning.

Evolutionary Timeline

Archean Era
4,500 - 2,500 mya (million years ago)

4,500 mya: The earth begins to form as dust particles condense into a hot, molten mass.

3,800 mya: The first known rocks form as the earth cools. The atmosphere is forming as gas escapes the earth's hardening crust. There is no free oxygen (O2). The cooling of the earth causes water vapor to condense and flood the earth, creating the oceans.

3,500 mya: The earliest known life begins. These single-celled organisms, prokaryotes, have no nucleus and resemble present day bacteria.

3,000 mya: The food source of the prokaryotes, the organic molecules of the oceans, has depleted. Prokaryotes that are self-feeding, autotrophic, have an advantage in survival and flourish. Prokaryotes develop photosynthesis, a process by which they combine carbon dioxide and water with energy from the sun to form simple sugars. As a byproduct of photosynthesis, free oxygen collects in the atmosphere.

Proterozoic Era
2,500 - 570 mya

2,000 mya: Prokaryotes branch out into many types of single-celled organisms.

1,200 mya: Eukaryotes, the first organism with a nucleus, may have originated, though this may not have occurred until later. Divergence of the plant and animal phyla.

1,000 mya: The evolution of sexual reproduction. This creates more diversity in organisms.

750 mya: Evolution of the first multicellular plants and animals (invertebrates).

Paleozoic Era
570 - 225 mya

570 mya: Cambrian period begins. First known arthropods, shelled ancestors of present-day insects. A wide variety of invertebrate species develops.

500 mya: Ordovician period begins. The first vertebrates, fish, evolve. Shell bearing invertebrates flourish.

435 mya: Silurian period begins.The first dry land plants develop. Arthropods become terrestrial. Armored fish flourish in the oceans.

395 mya: Devonian period begins. Forests of giant ferns are emerging on the land. Arthropods evolve into insects. Vertebrate fish evolve into amphibians and begin utilizing resources on the land.

345 mya: Carboniferous period begins.The surface of the earth is becoming dryer. Some amphibians evolve into reptiles.The first seed-bearing, or gymnosperm, plants and coniferous trees develop.

280 mya: Permian period begins. Forests of gymnosperm plants are replacing the primitive giant ferns. The first fossil record of the Dimetrodon, a mammal-like reptile which later evolves into the order Mammalia.

Mesozoic Era
225 - 65 mya

225 mya: Triassic period begins. Spread of mammal-like reptiles.The earliest dinosaurs evolve.

180 mya: Jurassic period begins. Dinosaurs dominate the earth.The first birds evolve from reptiles. Mammals first evolve from reptiles.

135 mya: Cretaceous period begins. Mammals at this time are small and divided into two major groups- marsupials and insectivores.

65 mya: Dinosaurs become extinct. Without competition from the large reptiles, mammals begin to proliferate. Evolution of flowering plants, or angiosperms.

Cenozoic Era
65 - 1.8 mya

65 mya: Tertiary period and Paleocene epoch begin. Mammals grow larger and fill the ecological niches that dinosaurs previously had. The earliest primates evolve. These primates were small insectivores who were most likely terrestrial. During this epoch, primates began to include food items such as seeds, fruits, nuts and leaves in their diet.

53.5 mya: Eocene epoch begins. Primates diversify and some become arboreal. Primates have developed prehensile hands and feet with opposable thumbs and toes and their claws have evolved into nails. Arboreal primates evolve relatively longer lower limbs for vertical clinging and leaping. Their eye sockets are oriented more frontally resulting in stereoscopic vision. Primates of this epoch belong to the prosimian family.

37.5 mya: Oligocene epoch begins. The anthropoid suborder of primates emerges with the platyrrhines (New World monkeys) and the Old World monkeys (of the catyrrhine family). The eye sockets of these primates become completely enclosed with bone and the snout decreases in size, which implies a greater reliance on sight and less on smell.

22.5 mya: Miocene epoch begins. Dryopithecines, the earliest apes (hominid superfamily), evolve in Africa.

5.5 mya: Pliocene epoch begins. Human-like apes evolve on the African savannas. These apes are bipedal and use tools to obtain food. Chimpanzee and gorilla ancestors diverge from the human ancestors.

2 mya: Appearance of Homo sapiens (humans).

1.8 mya: Quaternary period and Pleistocene epoch begin. Humans begin to use stone tools.

10,000 years ago: Holocene epoch begins. Humans first begin to domesticate plants and animals.