Week #14 - The Evolution of Primates: Leading to Human Evolution

The order Primates of the class Mammalia includes

Prosimians, Monkeys & Apes

Non-human primates:

Found primarily in the tropical or subtropical regions of South America, Africa and Asia.

• Range in size from the mouse lemur at 30g (1 ounce) to the mountain gorilla at 200kg (441 pounds).

Characteristics of Primates

• Hands and feet adapted to climbing trees – evolved from tree-dweller species

• Brachiation: swinging through trees using the arms

• Adaptations include:

  • Rotating shoulder joint

  • Big toe separated from the other toes (except humans)

  • Thumbs sufficiently separated from fingers to allow gripping branches

  • Stereoscopic vision: two overlapping fields of vision from the eyes which allow for depth perception and gauging distance

• Brains larger than that of most animals

• Claws modified into nails

• One offspring per pregnancy

• Trend toward holding the body upright

Order Primates is divided into 2 groups:

Strepsirrhini vs Haplorhini

Stepsirrhini (wet-nosed or turned-nosed)

• Tend to be nocturnal

• Have larger olfactory centers in the brain

• Exhibit smaller size and smaller brain

Haplorhini (dry-nosed or simple-nosed)

• Tend to be diurnal

• Depend more on vision than olfaction

• Exhibit larger body and brain size

Proto-primates

• The first primate-like mammals

• Roughly similar to squirrels and tree shrews in size and appearance

• Their evolutionary history is obscure due to their very fragmented and scarce fossil record (mostly from North America)

• The oldest known primate-like mammals with a relative robust record date ˜65 MYA

First true primates

• Date about 55 MYA

• Found in N. America, Europe, Asia, and Africa

• Resemble modern day pro-simians like lemurs and tarsiers

• Larger brains than proto-primates

• Larger eyes

• Smaller muzzles

Monkeys

• • Believed to have evolved from prosimians ˜40 MYA.

• Present in the “New World” (South America) and the “Old World” (Africa and Asia)

• There is still uncertainty regarding the origin of the New World monkeys

• New World monkeys appeared after the formation of the South American continent

• Ancestors of monkeys arose in the Old World, and somehow reached the New World

• Monkeys in the New World underwent an adaptive radiation differentiating from the Old World monkeys

New World Monkeys vs Old World Monkeys

• New World Monkeys (Platyrrhines): broad noses

• Old World Monkeys (Catarrhini): narrow downward pointed noses

So… did we evolve from monkeys?

• Kinda… but not exactly! Our ancestors evolved from catarrhines – monkey-like animals

• Those monkey-like animals were not the monkey species that exist today

• “If we evolved from monkeys, how come there are still monkeys around?”

• Well, because the modern monkeys also evolved from that shared common ancestor, but we evolved slightly differently

Apes

• Evolved from catarrhines (group that includes the Old-World monkeys) in Africa ˜25MYA

• Generally larger than monkeys and without tail

• All capable of moving through trees but spend most time on the ground

• Unlike monkeys, apes do knuckle walking

Gibbons

• Known as Lesser Apes

• Smaller than Greater Apes

• Little sexual dimorphism (in some species sexes differ in color)

• Longer arms than in apes for tree swinging

• Limited to Asia

Orangutans

• Believed to have split from African great apes 15-19MYA

• 3 species native to islands in Indonesia

• Borneo – Pongo pygmaeus

• Sumatra – Pongo abelii, Pongo tapanuliensis (Batan Toru forest in Sumatra)

Orangutan male longcall - function

• Attracting females for mating

• Repelling rival males and asserting dominance

• Communicating location

Gorillas

• All live in Central Africa

• The eastern and western “populations” are recognized as different species:

  • G. berengei (eastern)

    • Mountain gorilla

    • Eastern lowland gorilla

  • G. gorilla (western)

    • Western lowland gorilla

    • Cross river gorilla

why do gorillas chest beat

• Communicate dominance

  • Assert dominance

  • Avoid conflict

• Defense of territory

  • Warning intruders

  • Boundary marking

• Courtship and attraction

• Excitement or agitation

  • Playing

  • Frustration

• Mostly seen in male adults but females and juveniles do it too

Chimpanzees & Bonobos

• Chimps are considered to be the most closely related species to humans

• The species most closely related to chimpanzees is the bonobo

• Chimpanzee and human lineages split ˜6-8MYA

• Chimpanzee and bonobo lineages split ˜2MYA

Chimpanzees & Bonobos: • Both species live in Central Africa but are separated by the Congo River

Allopatric speciation

DIF Chimpanzees & Bonobos

• Bonobos are slighter than chimpanzees with longer legs and more hair on their heads

• Bonobos have higher-pitched voices than chimps

• Chimps are more aggressive and sometimes kill animals from other groups; bonobos do not!

• Chimpanzees are known to wage “wars” for long periods of time

Family Hominoidea

• Hominoids: Group that includes the lesser, great apes, and humans

• The fossil record and DNA evidence suggests that humans and chimpanzees diverges from a common hominoid ancestor 8-6MYA

• Within the branch of humans (Hominins) our species is the only surviving

Hominins

• Hominins refers to the species that evolved after the split leading to humans and chimpanzees.

• Hominin species are more closely related to us humans than chimpanzees (we are included in the group!).

• Marker features that distinguish hominins from other hominoids include:

  • Bipedalism (upright posture)

  • Increased size of the brain

  • Fully opposable thumb that can touch the little finger

The challenge of determining lines of descent

• A difficult task!

• In the past, scientists believed that we could organize them in a certain linear order, from older to younger, and demonstrate the course of evolution up to humans.

• Many species co-existed according to the fossil record

• Many species died out and do not seem to be ancestral to human

Early Hominins: Genus Australopithecus

• Australopithecus – Southern ape

• Genus of hominin that evolved in eastern Africa ˜4MYA and went extinct ˜2MYA

• Several species known, but more evidence for A. afarensis (lived 4-3MYA)

• Scientists believe that our genus Homo evolved from a common ancestor shared with Australopithecus ˜2MYA

• More similar to non-hominin apes

• Exaggerated sexual dimorphism

  • Males 50% larger than females

• Brain smaller than humans relative to body size (similar to non-hominin apes)

• Trends towards modern species

  • Bipedalism

    • Although it likely spent time in trees

  • Similar footprints to those of modern humans

  • Canines and molars smaller than in apes but larger than in modern humans

  • Prominent jaw

  • Presence of forehead (but smaller and sloped)

Australopithecus afarensis fossil

• Found in mid-70s in the Afar region of Ethiopia in Africa

• Adult female

• The most complete fossil found for an australopith

• 40% of the skeleton recovered!

Early Hominins: Genus Paranthropus

• Dated ˜2.5MYA

• ˜4.5ft tall (1.35m)

• Molars show heavy wear suggesting a diet of coarse and fibrous vegetation, contrasting with the partially carnivorous diets of australipths

• P. robustus, P. aethiopicus, P. boisei

• Believed to not be ancestors of modern humans

Early Hominins: Genus Homo

• Appeared ˜2.5-3MYA

• For a long time H. habilis was believed to be the oldest species in the genus

• H. gautenensis was found in 2010 (in S. Africa) and is believed to be older species

Genus Homo: Homo habilis

• More features similar to humans than other previously described hominins

• Jaw less prognathic than australopiths

• Larger brain, closer to modern human size

• Still had long arms similar to older hominins

• Homo habilis means “handy man”, a reference to the stone tools found near its remains

Genus Homo: Homo erectus

• Appeared ˜1.8MYA ago

• Believed to have originated in Africa and migrated to India, China, Java ( island in Indonesia), and Europe

• Several specimens: Peking man, and Java man

• More similar to modern humans than H. habilis

• Closer in size to modern humans

• Males were 20-30% larger than females

• More downward-facing nostrils (not forward)

• Artifacts suggest they were the first hominin to:

  • Use fire, hunt, have a homebase

• Believed to have lived until ˜50k years ago

Genus Homo: Homo sapiens

• Several presumed sub-species (a.k.a. archaic Homo sapiens): • Homo heidelbergensis (Europe, Africa, Asia) • Homo rhodesiensis (Africa) • Homo neanderthalensis (Europe and Asia) • Homo denisovans (Asia - Siberia)

• Presumed to have evolved from Homo erectus ˜500k years ago

• These species survived until ˜30-10k years ago, having co-existed with H. sapiens sapiens

Members of the superfamily Hominoidea:

• 1.Lesser Apes (Family: Hylobatidae)

  • 1.Gibbons (Hylobates species)

• 2.Great Apes (Family: Hominidae)

  • 1.Humans (Homo sapiens) 2.Chimpanzees (Pan species) 3.Gorillas (Gorilla species) 4.Orangutans (Pongo species)

• Hominoidea encompasses both families:

  • Hylobatidae (lesser apes)

  • Hominidae (great apes and humans)

    • Within Hominidae there is the tribe of hominins (Genus: Australopithecus, Paranthropus, Homo