Hominid Evolution: On The Origin of Humans

Questions to answer:

• How did we evolve into humans?

• What is the relationship between humans and other

primates?

• What is a hominid?

• What were early humans (hominids) like?

• How long have humans (hominids) been around?

• Where - and when - did modern humans

(Homo sapiens) originate?

• How have we changed?

• How did we come to populate the entire earth?

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Evolution of Primates

• The evolution of primates is

characterized by:

– mobile limbs

– grasping hands (with opposable thumbs)

– a flattened face

– binocular vision

– a large, complex brain (for learned

behavior)

– a reduced reproductive rate

Mobile Limbs

• Most primates have flat nails as well as

sensitive pads on the undersides of

fingers and toes.

– Many also have both an opposable big toe

and thumb.

• Mobile limbs and clawless opposable

digits allow primates to freely grasp and

release tree limbs.

Primate Hands

Binocular Vision • Stereoscopic vision and resultant depth

perception allows primates to make

accurate judgments about distance and

position of adjoining tree limbs.

Evolution of Primates

• Prosimians were the first type of primate to

diverge from the ancestral primate line.

• Surviving anthropoids are classified into three

superfamilies.

– New World monkeys

– Old World monkeys

– Hominoids

What is a hominid?

• Any human-like

species, including us.

• Bipedal (walks on two legs).

• Intelligent (large brain, uses

tools).

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Hominids are not the same as modern apes.

• Modern apes like chimpanzees,

gorillas, orangutans are not

bipedal.

• Modern apes do not have a large

brain case compared to ours.

• Modern apes do not make tools.

• However, chimpanzees are our

closest relative - our DNA is 98%

similar to theirs!

There have been at least a dozen different species of hominids

over the last five million years or so.

Since the first hominid fossils and artifacts were found, we

have found literally hundreds of others.

Anthropologists

compare the skulls,

teeth, bones, and

tools.

Together they begin

to show our family

tree - how we evolved

to who we are today.

Notice that most

species have gone

extinct - there are a lot

of “dead ends”.

Hominoid Evolution

• Proconsul is believed ancestral to hominids.

Hominids

• To be a hominid, a fossil must have an

anatomy suitable for standing erect and

walking on two feet.

– Bipedalism

• Human anatomy differs from that of an ape

largely because humans are bipedal while apes

are quadrupedal.

Australopithecines

• It is possible that one of the

australopithecines that evolved and

diversified in Africa 4 mya is a direct

ancestor of humans.

– Southern Africa

• Australopithecus africanus

– Eastern Africa

• Australopithecus afarensis (Lucy)

Australopithicenes

Australopithicenes

“Lucy In The Sky With Diamonds.”

• Discovered in Ethiopia in 1974.

• Dated at 3.2 million years old!

• 40% of her skeleton was found.

• Only four feet tall.

• Bipedal for certain. She walked upright.

• Her scientific name is Australopithecus afarensis, a distant ancestor to us, Homo sapiens.

An even more impressive fossil was found in

1978, but there were no bones to it at all.

Huh?

This discovery proved that there were

bipedal hominids even earlier than Lucy.

The Laetoli Footprints

• 3.6 million years old.

• Even older than Lucy.

• Clearly bipedal.

• Also showed that these early

hominids walked together.

So who were the “first” hominids? We still are not sure, but

we have found more fossil fragments as early as five million

years ago.

Human Evolution

Comparative Brain Sizes

Hand Shape

• Development of

more flexible

opposable thumb

• Allowed advanced

tool use

Pelvis shape

• Allowed early

hominids to

stand & walk

upright

• Gave advantage

of being able to

see around

them on the

savannah

Spine Shape

Changed

from "C"

shape to "S"

shape

Jaw Size •Jaw has reduced in size, reflecting changes in species diet

•Size of teeth have generally decreased, especially canines

Hominid changes over time

And when did our species - Homo sapiens - first evolve?

And how did we come to dominate the earth?

Classification Hierarchy

Kingdom Animal

Phylum Chordate

Class Mammal

Order Primates

Family Hominids

Genus Homo (“man”)

Species Sapiens (“wise”)

It is important to remember that there were several species in

the genus Homo that came before Homo sapiens.

• Homo habilis is the

earliest fossil

discovered so far.

(2.3 million years old)

• It means “handy man”.

• Homo habilis used very

simple tools.

Homo habilis

Homo habilis contd.

Homo erectus was a serious toolmaker and a fine hunter.

Evidence also indicates that they were the first to use fire.

Homo erectus

• ~ 1.5 Million years - ~ 80,000*

years . Homo erectus.

–Larger than H. habilis

–Larger brain

–Smaller face

–Was the first to use fire

–Allowed man to "break out" of Africa

into Europe & Asia

Homo erectus

Fossils of several other species in the genus Homo

have also been found.

• Homo ergaster.

• Homo heidelbergensis.

• The most famous is Homo

neanderthalensis

(Neanderthal Man).

• Neanderthal Man lived in

Europe.

• They too went extinct.

• Probably lived side-by-side with

Homo sapiens.

• Possibly interbred with them.

Homo neanderthalis

~130,000 - 30,000 years. Homo

neanderthalis "Neanderthal man"

– Probably not a direct ancestor - but

another offshoot from H. erectus

– Shorter, stockier, stronger than modern

man. Adapted to ice age.

– Larger brain size than modern man.

– Buried dead with flowers - first evidence of

religeous/symbolic thinking.

H. neanderthalis

And then there is…

Homo sapiens.

Anatomically modern humans.

• Oldest fossils found

so far are perhaps

195,000 years old.

• Found in Africa (also

in Ethiopia).

“Modern” man

• ~ 100,000 years to present - Homo

sapiens (modern man).

• Appears to have originated from H.

erectus in Africa, then migrated

outwards to Europe & Asia.

• Replaced existing species H. erectus &

H. neanderthalis

How to make a human: • Millions of years

ago, a majority of

northern Africa

was rainforest.

Ancestors to

man

Rapapithecus

and Proconsul,

were full arboreal

apes living in

these forests.

Changes • However,

approx. 5

mya the great

rift valley

formed in

east central

Africa.

Problems….. • The effect of this rift:

– isolated the ape population from the west

– created a “rainshadow desert”

Change of environment.

• change in precipitation

changed the landscape

from rainforest to

savannah

• apes developed new

form of transportation

since they could no

longer go through the

trees

• evolved the ability to

walk upright

Does that mean we all come from

Africa?

Yes! And recently, DNA analysis has proven this.

We are all Africans.

• DNA testing of thousands of

humans today, using a

simple saliva test kit, has

created a “map” of human

migration since modern

humans first left Africa

80,000 years ago.

We now have an excellent “road map” of how humans evolved

from Africa and migrated to populate the rest of the earth.

This evidence matches the fossils and fills in the gaps.

And if we follow the path of our

mitochondrial DNA back to the

beginning, somewhere in Africa…

We find that all humans alive today, including us, descended

from a SINGLE FEMALE.

Scientists have called her “Eve”.

From Lucy to “Eve”.

• Using fossils, artifacts, and

now even our DNA, we are

slowly getting a good picture

of our own hominid

evolution.