primates


 * Primate **

The order **Primates** (pronounced /ˈprаɪmeɪt/) belongs to the Mammalia class, Chordata phylum, and Animalia Kingdom. They include lemurs, monkeys, apes, and humans. Primates are characterized by their good eyesight, flexible hands and feet, and sophisticated social structures. The two subgroups of primates are the Prosimii and Anthropoidea. Primates are arboreal but include ground-dwelling species as well. With the exception of humans, primates are found primarily in the tropical regions of the world.

1. Classification 2. Evolutionary History 2.1 Homo sapiens 3. Anatomy 4. Behavior 5. Diet 6. Habitat ||
 * Contents

A group of primates in their own habitat. (EK)



Classification

The two subgroups of primates are the Prosimii and Anthropoidea.
 * Prosimians** are also known as “premonkeys.” They are thought to resemble early arboreal primates. Prosimians were the first subgroup to evolve and are also refered to as "lower primates" ( 2 AL). Examples include the lemurs of Madagascar and the lorises, pottos, and tarsiers that live in tropical Africa and southern Asia. Prosimians exhibit lower intelligence than anthropoids and they most closely resemble other mammal groups (for example, they typically have whiskers and extended snouts) (8 MB).
 * Anthropoids** include monkeys, humans, and the four genera of apes: //Hylobates// (gibbons), //Pongo// (orangutans), //Gorrilla// (gorillas), and //Pan// (chimpanzees, and bonobos). Anthropoids are larger than prosimians and have much longer life cycles, allowing some to reach a hundred years of age. (2 AL) Also, Anthropoids are distinguishable from Prosimians by their arm length--lemurs and such have arms shorter than their legs, while monkeys and apes' arms are equal or longer in length than their legs. (AR 11)

Two commonly confused terms used by paleoanthropologists are hominoid and hominid. **Hominoid** refers to great apes and humans. Hominoid fossils are related to us, but they are more closely related to chimpanzees, gorillas, and orangutans. **Hominids** refer to species more closely related to us. The two main groups of hominids are the australopithecines, which are now extinct, and members of the genus //Homo//, with only one remaining species //Homo sapiens//.

Evolutionary History

Fossil records indicate that 40 million years ago, monkeys established themselves in both the Old World (Africa and Asia) and the New World (South America). During their time apart, the Old World and New World monkeys underwent separate adaptive radiations. Old World monkeys include ground-dwelling as well as arboreal species such as macaques, mandrills, baboons, and rhesus monkeys. They lack prehensile tails, their nostrils open downward, and they are characterized by a seat pad. All Old World monkeys are arboreal. They have prehensile tails, tails adapted for grasping, and nostrils that open to the sides. Examples include spider monkeys, squirrel monkeys, and capuchins.



Paleoanthropology **, the study of human origins and evolution, focuses on the time during which humans and chimpanzees diverged from a common ancestor. Humans and apes diverged from a common hominoid ancestor somewhere between 5 and 7 million years ago. The discovery of //Australopithecus anamensis// indicates that hominids were bipedal (they walked on two feet) at least 4 million years go. The discoveries of //Australopithecus africanus// and //Australopithecus afarensis,// more commonly known as “Lucy,” all provide further evidence for the origin of bipedalism. Bipedalism is an essential evolutionary trait. Two extra hands allowed Lucy gain access to more kinds of food, make tools, and see predators in the distance(JE).
 * Homo Sapiens ****

The earliest known (and recently discovered) common ancestor of humans and Apes is //Ardipithecus ramidus//. “Ardi” was found in strata that was dated to 4.4 million years ago, in an area that was thickly forested. This new species had teeth that were similar to later ape descendents, but it had certain hominid dental features, such as low, blunt canines and incisors that were smaller than those of modern chimpanzees but larger than those of Australopithecines. The cranial structure of //A. ramidus// also seemed to rest on top of the vertebral column, suggesting it was bipedal (DPOD 13). The earliest fossils that anthropologists place in genus Homo are classified as //Homo habilis// for “handy man.” Their fossils age from 2.5 to 1.6 million years old. //Homo habilis// have less prognathic jaws and larger brains than //Australopithecus africanus// indicating the evolution of characteristics further resembling the modern human. //Homo erectus// was the first hominid species to migrate out of Africa. Their fossils have been found in Asia and Europe, and they lived from 1.8 million years ago to 500, 000 years go. //Homo erectus// had even larger brains compared to //Homo habilis.// Similar to //Homo sapiens//, Males of //Homo erectus// are only 1.2 times the size of females. Anthropologists interpret this finding as the replacement of polygamy with monogamy because in polygamous relationships, the largest, strongest males outcompeted smaller males. There are two hypotheses for the origin of //Homo sapiens//, anatomically modern humans. The **multiregional hypothesis** view //Homo erectus// as “archaic Homo sapiens.” //Homo erectus// migrated to various continents outside of Africa between 1 and 2 million years ago. Supporters of this hypothesis believe modern humans evolved from the interbreeding of //Homo erectus// in various regions. The second hypothesis is the **“out of Africa” hypothesis** or the **replacement hypothesis**. Advocates of this hypothesis argue that only the African descendants of //Homo erectus// that left 100, 000 years ago gave rise to all the diverse human populations. Other regional descendents of //Homo erectus//, including Neanderthals, became extinct without contributing to the gene pool of modern humanity. Regardless of which hypothesis scientists believe in, there is general consensus in the scientific community that humanity has its origins from Africa based on fossil evidence.



3 Most common Misconceptions about Human Evolution 1) Our ancestors were chimpanzees or any other modern ape. Humans did not evolve from chimpanzees because chimpanzees and humans diverged from a common ancestor. 2) Human evolution is a ladder with a series of steps leading up to //Homo sapiens//. During times in hominid history, several different human species coexisted. //Homo sapiens// did not evolve from one hominid to the next; they are simply the only remaining branch of the Homo phylogeny. 3) Human characteristics evolved in unison. Different human characteristics evolved at different rates or in “**mosaic evolution**.” Bipedalism, our erect posture, evolved before our enlarged brains.

Major Features of Human Evolution
 * Brain size** – modern humans have triple the brain volume of primitive hominoids
 * Jaw Shape** – modern humans no longer have the lower **prognathic jaws** (protrusion of the jaw, especially lower jaw) (15 HL) our hominoid ancestors had. Our faces are thus flatter with a more pronounced chin.
 * Bipedal Posture** – our hominoid ancestors walked on all four limbs as all modern apes do. Upright posture and two legged walking are associated with major skeletal modifications evident in early hominid fossils.
 * Reduced Size Difference Between the Sexes** – this is also known as sexual dimorphism. ( 2 AL) A male gorilla can weigh almost double that of a female. In humans the male is only about 1.2 times the weight of a female.
 * Changes in Famimly Structure** - Unlike most ape and monkey species, humans are monogamous (in most cultures)- humans have one mate for life, facilitating long-term pair bonding. Human infants are exceptionally dependant on their mothers, and parental care lasts longer in humans than in other ape species. It can be speculated that the behavioral complexity of humans stems from the effects of extended parental care coupled with larger brain size. (9RM)
 * Thumbs**- Primates have opposable thumbs and big toes to grasp with the hand and foot. Human thumbs are longer than those of other primates, which allows for fine control (22 SC).
 * Spine**- humans have a lumbar curve in the spine (22 SC).
 * Knee-** Humans have a stable knee for walking, and other primates have a mobile knee to climb (22 SC).

Anatomy

Compared to other mammals, primates have large brains and short jaws, giving them a flat face. Their eyes are located close together on the front of the face. Overlapping fields of vision of the two eyes enhance depth perception which helps with arboreal maneuvering. Primates have flat nails rather than narrow claws and skin ridges on their fingers. Modern apes, except gibbons, are larger than monkeys. They have long arms, short legs, and no tails. Most primates have hands and feet adapted for arboreal life. All modern primates have a big toe that can separate widely thus enabling them to grasp onto branches with their feet. These limbs that can grasp branches (or other objects) are referred to as "prehensile" (SW 12). Many New World monkeys have prehensile tails as well as prehensile hands and feet (SW 12). The thumb is relatively mobile and separate from the fingers in all primates, but a fully opposable thumb is found only in anthropoid primates. An **opposable thumb** is an arrangement of the fingers such that the thumb can touch each fingertip of all four fingers. Diagnostic characteristics of primates include their large brains, short jaws, and opposable thumbs. Behavior

Most monkeys are diurnal and live in bands held together by social behavior. Primates have well-developed parental care and relatively complex social behavior. Chimpanzees and gorillas are highly social and possess the most complex social structure. Primates generally form communities that are closed to contact with members of other communities. Encounters can range from aggression, to friendly greetings (mostly in chimpanzees), to harmless intimidation rituals. Some primates such as Howler monkeys and Gibbons converge with other groups near the terrestrial border and make hostile displays. Dominance hierarchies are also common in which the alpha male and alpha female (highest ranking individuals) gave the most privileges involving access to resources and mating opportunities (4 KA). media type="youtube" key="U64k_fA2Rcc" width="425" height="350" An example of the intelligence and skill of primates. Koko, the gorilla, knows more than 1000 different signs, all learned within the first couple years of the project. The fact that Koko attempts to make a butterfly with her hands is quite remarkable because gorillas do not possess the thumb dexterity required to interlock her two hands. (12 AS)

Diet

Primates are generally omnivorous, which means that they can eat both plants and animals for nutrition (13 J Stein). Fruit provides easily digestable carbohydrates and lipids. Leaves and insects are also required for vitamins and minerals. Some primates have anatomical specializations that enable them to exploit particular foods, such as fruit, leaves, gum, or insects. For example, the howler monkey has an extended digestive tract that allows nutrients to be absorbed from leaves that can be difficult to obtain otherwise (EK2).

Habitat

Modern apes are found exclusively in tropical regions of the Old World. //Homo sapiens// on the other hand are found throughout the world. Primates can be found in evergreen tropical forests, dry scrub forests, dry areas that have forests along river banks, coastal scrublands, bamboo stands, and dry deciduous forests. (J. Sun 22) Some species of primates are good swimmers and are even comfortable near swamps and other bodies of water. (21 DC).

Review Questions

1. What are the differences between the "multiregional hypothesis" and the "out-of-Africa hypothesis?" What are their similarities? How does this relate to all primates? (AN) 2. In what ways do the two primate subgroups, Prosimians and Anthropoids, differ with respect to their evolutionary history, their characteristics, and their cognitive capabilities? In other words, what distinguishes the two subgroups (8 MB)? 3. What evolutionary trait did "Lucy" provide evidence of and why is it important to our species? (AW) 4. What are the three most common misconceptions about human evolution? (CH) 5. How do primates exhibit social behavior within their surroundings? (23 VK)

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By: Celine Hu