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Chapter 16 -- Primate Evolution
Transcript of Chapter 16 -- Primate Evolution
Hominoids to Hominins
Primates are a diverse group of mammals that includes humans, apes, monkeys, and lemurs.
There are more than 200 living species
Most are arboreal -- they live in trees
A few are terrestrial -- live on ground
Primates possess many adaptations to allow them to dwell successfully in trees:
flexible hands and feet
All nonmonkey anthropoids -- gibbons, orangutans, chimpanzees, gorillas, and humans.
Hominins are a subgroup of hominoids that includes humans and other (now extinct) human-like primates.
The earliest fossils to show some degree of bipedalism date back to 6-7 million years.
In the last 30 years, many more hominin fossils have been discovered, and it is difficult to classify some of them. Scientists are still working to understand how they are all related.
It is believed that the
descendants of the australopithecines, though the fossil record is so far a bit too sparse to confirm this.
Homo neanderthalensis evolved exclusively in Europe and Asia likely from H. erectus or another intermediary.
The species Homo sapien (also referred to as Cro-Magnons) has displaced the Neanderthal population.
1) Describe characteristics of primates.
2) Compare major primate groups.
3) Trace the evolution of primates.
4) Describe hominoid and hominin features.
5) Trace hominoid evolution from Proconsul to Homo.
6) Compare various australopithecine species.
7) Describe species in the genus Homo.
8) Explain the Out-of-Africa hypothesis.
9) Compare Neanderthals and modern humans.
Characteristics of Primates
Manual Dexterity -- flexible hands and feet
typically 5 digits on each hand and foot
flat nails and sensitive fingertips
opposable first digits (thumb)
Senses -- favor vision over smell
binocular vision (eyes in front)
Diurnal (active during day) -- color vision
Few nocturnal (active at night) -- B&W vision
Smaller, flatter noses; reduced, unspecialized teeth
Locomotion -- ability to move around
limber shoulders and hips
primarily rely on hind limbs
Complex brains and behaviors
large brain for body size
memory and coordination
social behaviors: grooming, communicating, facial expression
one at a time
Have large eyes and ears, rely more on smell, mostly nocturnal.
once classified as a strepsirrhine
more closely related to
Anthropoids -- large-brained diurnal monkeys
split into three groups:
New World Monkeys (Americas)
about 60 species
have prehensile tail
Old World Monkeys (Africa, Asia, Europe)
about 80 species
larger, more time on ground
Homonoids -- nonmonkey anthropoids (Apes)
Great Apes (hominid family)
chimpanzees and bonobos
It is believed that primates may have evolved from ground dwelling animals who began searching for food in trees as flowers and fruit evolved.
DNA evidence suggests that primates first lived about 85 mya. The oldest known fossil evidence is from about 60 mya.
One of the earliest primate fossils is called
It resembles a tiny tree shrew, but has some features similar to lemurs today.
Around 50 mya lemurlike primates were widespread and many species existed. Around this time anthropoids diverged from the tarsiers, they leapt less, walked more, but still had small bodies and brains.
Around 30-35 mya anthropoids were diverse and widespread, however by the end of the Eocene many strepsirrhines went extinct, likely due to climate changes.
Many anthropoid fossils have been found in the Fayum basin of Egypt. Now a dessert, it was a tropical region when dozens of anthropoid species lived there 36-31 mya.
The largest fossil, called
is believed to be the one of the first apes
to split from the Old World Monkeys.
The fossil record for early hominoids is sparse, but DNA technology has allowed scientists to determine the potential divergence of the
largest of the primates
largest brain in relation to body size
flexible arms and shoulders
upright or semi-upright posture
arms longer than legs (except hominins)
When tropical forests in Africa began to shrink, new hominoids evolved as they adapted. Around 23-14 mya, as many as 100 hominoid species existed. Many migrated from Africa to Europe and Asia.
One of the earliest Hominoid fossils,
, was discovered in Kenya. They has smaller brains, lived predominantly in trees, but may have had the ability to walk upright.
Some scientists believe this may be an ancestor of the human line of decent.
The lineage that lead to hominins likely split from African apes 8-5 mya.
Humans are the only remaining hominin species.
more complex brains
higher level thinking
thinner and flatter face
longer thumbs and flexible wrists (manual dexterity)
bipedal -- walk on two legs
Quadrupeds to Bipeds
Hominins developed a fully upright stance, shortened arms, restructured pelvic bones and foot bones, and a change in the position of the head on the spinal cord.
not as fast
easier to be seen
strain on back/hips
uses more energy (defies gravity more)
Advantages of Bipedalism:
can be more efficient over long distances
easier to spot distant food
reduces exposure to sunlight
increases exposure to cooling winds
hands free to carry tools
Standing upright may have been an adaptation that was advantageous in the increasingly drier African environment.
The first hominins found that were truly bipedal are the Australopithecines who lived in Africa 4.2 - 1 mya.
They were small -- about 1.5 m tall, had apelike brains and jaws, but humanlike limb joints and teeth.
In 1974 an australopithecine fossil was discovered with hip and knee joints that indicated that she walked upright, though her brain was still small, she was nicknamed Lucy.
Scientists continued to debate about the details of primate evolution, for instance, whether large brains or bipedalism evolved first.
Footprint fossils were later discovered that provide further evidence that these early hominins were bipedal.
In addition to many australopithecines, other more robust hominins classified as paranthropoids have been found.
It is believed that hominins branched into many different lines, or offshoots, from their primate ancestors, and thrived between 2 - 1.2 mya.
By 1 mya, however, all hominins disappear from the fossil record, except those belonging to the genus
Characteristics of Homo:
earliest known member of the genus Homo
called "Handy man" due to use of stone tools
lived 2.4 - 1.4 mya
brain was 20% larger than australopithecine
more human-like teeth
could climb trees
even larger brain
longer legs and shorter arms
lived 1.8 - 1.3 mya
believed to have first human-like nose (pointed down)
made hand axes and other tools
appears to have been both hunters and gatherers
migrated in large numbers to Asia, maybe Europe
believed to be human ancestor
lived between 1.8 mil - 400,000 ya in Asia
appears to have evolved from
includes "Java Man" found in Indonesia
"Peking Man" found in China
longer skull, lower forehead
thicker facial bones, more prominent brow ridge
used tools, as well as fire
sometimes lived in caves
adapted successfully to many environments
found on an Indonesian island
about 18,000 years old
only 1 meter tall -- nicknamed "The Hobbit"
debated whether or not a new species
possibly dwarfed early human
wrist bones appear more ape-like
Many transitional fossils have been found with a mixture of traits of both H. erectus and H. sapiens. They are often put in this separate species group.
more muscle mass
bony brow ridges
Neanderthals lived during the ice age, hunted, built fires and shelters, cared for sick, buried dead, may have had language.
It was originally believed that the Neanderthal species was separate from our homo sapien ancestors and died out completely, however, DNA evidence suggests that they did interbreed with our ancestors.
Do you have
Characteristics of Homo sapiens:
made sophisticated hand tools
Homo sapiens first appear in the fossil record in Africa, they then migrate out, and they currently occupy all continents
Some scientists believe that modern humans evolved from separate Homo species at the same time in different areas of the world. According to this model, modern human races arose through convergent evolution.
Most scientists follow the Out-of-Africa hypothesis, which proposes that modern humans evolved once, in Africa, and then migrated all over the planet, displacing other hominins.
The Out-of-Africa hypothesis is supported by analysis of mitochondrial DNA. Mitochondrial DNA is only inherited from one's mother, and has changed very little over time.
All human mitochondrial DNA is nearly identical, with that of the African population varying the most -- this supports the idea that they have been around the longest because their DNA has had more time to develop variation.
Study of the Y chromosome yielded similar results.
The Beginning of Culture
The earliest evidence of culture dates back just
40,000 years ago in Europe.
Early humans expressed themselves with cave paintings and decorative artifacts.
They developed sophisticated tools and weapons, domesticated animals, and tailored clothing.