Humans as Primates

Objectives

– Describe primates and their

evolution.

– Describe the major anatomical features that define humans as primates.

– Outline the trends illustrated by the fossils of early man.

Primate evolutionTherapsids were the reptilian ancestors of mammals.

Eozotrodon was an early mammal 200 mya.

Therapsid

Eozotrodon,an insectivore

The 3 mammal lines present today

Primate evolutionOrigin in Asia ~85 mya?

Migration to Africa as Pangaea broke up.

Millions of years ago

Characteristics of primates

As mammals, all species have fur and produce milk.Primates have hands and feet adapted for grasping.They have relatively large brains and short jaws.

They have flat nails, not narrow claws.They have well-developed parental care

and complex social behavior.

Characteristics of primatesThe earliest primates were probably tree dwellers.

Opposable thumb (toe) for hanging on tree branches.The overlapping (binocular) fields of vision of the two eyes enhance depth perception – an advantage when jumping from branch to branch.

Characteristics of primatesTwo main groups of primates:

Prosimians resemble early tree-dwelling primates.Lemurs of Madagascar and the lorises, pottos, and tarsiers of tropical Africa and southern Asia.

Nocturnal species (large eyes, black/white vision).

Lemurs - note large eyes (black & white vision)

Characteristics of primatesTwo main groups of primates:

Anthropoids (of human likeness)Monkeys, apes (gibbons, orangutans, gorillas, chimpanzees, and bonobos), & humans.

Apes have no tails, unlike monkeys.

Day-active (smaller eyes with color vision).

Human evolutionHumans & apes share all but the last 5 million

years of evolution.Hominoid refers to great apes and humans collectively.Hominid means “man-like” - primate that walks on two feet (no opposable toe).

There are 2 main groups of hominids: the australopithecines, which came first and are all extinct, and members of the genus Homo, with all species extinct now except one: H. sapiens.

Human evolutionEvolutionary trends

Bipedalism vs. arboreal (life in trees).Increased stature: early Australopithecenes were chimp-sized; modern humans are much larger.Dietary specialization: tooth size has shrunk (jaw is smaller, making slope of forehead steeper), and incisors are less obvious (not for defense).More parental care: humans are born helpless.Cranial capacity: three-fold increase in brain size

Human evolutionEvolutionary trends

Bipedalism vs. arboreal (life in trees).Man’s body is centered over the pelvis.Femur attachment altered.Arms are shorter.

No knuckle walking

Human evolutionEvolutionary trends

Bipedalism vs. arboreal (life in trees).Climate change made forests disappear.Weaker “apes” were pushed out of remaining trees.On the ground, humans needed to see over the grass to spot predators (lions) before they saw them.

The Serengeti Plain of Africa where humans evolved

Human evolutionEvolutionary trends

Increased stature: early Australopithecenes were chimp-sized; modern humans are much larger.

Chimp Australopithecus Human

Human evolutionEvolutionary trends

Dietary specialization: tooth size has shrunk, and incisors are less obvious (not for defense).

Diet switched from plant to cooked animal food.Requires less grinding of food

Also, jaw is more V-shaped, less U-shaped

Human evolutionEvolutionary trends

More parental care: humans are born helpless.Length of care increases with brain size.

Humans require care through early teen years.

Human evolutionEvolutionary trends

Cranial capacity: a three-fold in-

crease in brain size

Upright stance narrows birth

canal, so a large head can

make birthing more difficult.

Face is more vertical as time passes.

Organization of the nervous systemThe brain’s anatomy

Conscious thought resides in the forebrain.Reflexes & voluntary movement are controlled by the midbrain.Vital body functions & co-

ordination are controlled by the hindbrain.

Front Back

Organization of the nervous systemThe brain’s anatomy: the forebrain

The cerebrum is for conscious thought.Two hemispheres manage different tasks.The corpus callosum connects the two halves of the brain.

Crossover in the corpus callosum causes the left hemisphere to manage the right side of the body.

Organization of the nervous systemThe brain’s anatomy: the forebrain

In the cerebrum, nerve connections create memories.

Cerebral cortex: the outer surface (gray matter) where infor-mation processing occurs is composed of nerve cell bodies. White matter consists of the connecting cables of nerve cells (the axons).

The many folds increase surface area = more nerve cells.

Organization of the nervous systemThe brain’s anatomy: the forebrain

The cerebral cortex is divided into 4 sections called lobes.

Frontal Lobe - reasoning, planning, parts of speech, move- ment, emotions, and problem solving.Parietal Lobe - movement, orientation, recognition, and perception of stimuli.

Occipital Lobe - visual processing.Temporal Lobe – per- ception and recognition

of sounds, memory, and speech.

Organization of the nervous systemThe brain’s anatomy: the forebrain

The hypothalamus controls the autonomic nervous system. It synthesizes and secretes hormones that stimulate or inhibit the secretion of pituitary hormones, which then control body tem- perature, hunger, thirst, fatigue, sleep, and circadian cycles

(like menstruation).Above the hypothalamus lies the thalamus, a major clearinghouse for infor-mation going to and from the spinal cord and the cerebrum.

Organization of the nervous systemThe brain’s anatomy: the midbrain

The uppermost part of the brain stem; relays information associated with vision, hearing, motor control, sleeping & waking, arousal (alertness), and temperature regulation.

Organization of the nervous systemThe brain’s anatomy: the hindbrain

Composed of the pons, medulla oblongata, and cerebellum.

The oldest part of the human brain.

The cerebellum is for balance. (Remember: humans are bipedal.)

Organization of the nervous systemThe brain’s evolution

The human brain has a largecerebrum with many folds

to increase surface area.

Brains of primates(also note the cerebellum)

Physical vs. cultural evolutionThe human state of consciousness

Human Evolution

Characteristics of primates

As mammals, all species have fur and produce milk.Primates have hands and feet adapted for grasping.They have relatively large brains and short jaws.

They have flat nails, not narrow claws.They have well-developed parental care

and complex social behavior.

Human evolutionHumans & apes share all but the last 5 million

years of evolution.Prosimians are the nocturnal “pre-monkeys”.Anthropoids are the day-active monkeys, apes, & humans.Hominoid refers to great apes and humans collectively.Hominid means “man-like” - primate that walks on two feet.

There are 2 main groups of hominids: the australopithecines, which came first and are all extinct, and members of the genus Homo, with all species extinct now except one: H. sapiens.

Human evolutionEvolutionary trends

Bipedalism vs. arboreal (life in trees).Increased stature: early Australopithecenes were chimp- sized; modern humans are much larger.Cranial capacity: three-fold increase in brain size Neoteny: retention of some juvenile characteristics in an animal that seems otherwise mature.More parental care: humans are born helpless.Dietary specialization: tooth size has shrunk, and incisors are less obvious (not for defense).

Hominids coexistedAt various stages in hominid evolution, several

species may have coexisted.Isolated groups evolved into separate species; some persisted and others went extinct.

Hominid fossil recordThe fossil record is incomplete, resulting in

uncertainties about human evolution.How did one type change into another?

Where are the intermediates? Large gaps exist.

Hominid fossil recordpre-Homo hominids are classified as

australopithecines – the “southern apes”.They lived from 4.3 to 1.3 mya.First discovered was Australopithecus africanus (1924) by Raymond Dart in a quarry

in S. Africa.Evidence of bipedalism and

human-like hands and teeth.No opposable toe as in other primates.

Brain was only ~1/3 the size of a modern human's, ~27 in3.Lived 2.3 – 3 mya.

Hominid fossil recordAustralopithecines

In 1974, an older fossil, ~40% complete, discovered in the Afar region of Ethiopia. Nick-named “Lucy”; described as A. afarensis.

Brain the size of a chimpanzee. Pelvis and skull bones and fos- sil tracks showed bipedalism.

(Up-right walk evolved before the larger brain size).

Lived 2.8 – 3.6 mya inAfar region of Ethiopia

Hominid fossil recordAustralopithecines

Two more lineages appeared after A. africanus, living in Africa between 1.3 and 2.3 mya.:

Both were “robust” forms with sturdy skulls and powerful jaws and teeth for grinding tough foods, like A. robustus (below) .Both forms were a dead end.

Hominid fossil recordThe earliest fossils in genus Homo are of H. habilis.

Range in age from 2.5 to 1.6 million years old.Coexisted for 1 million years with Australopithecus

Lived in E. Africa.Brain size ~47 in3.“Handy man”,

used stone tools.Unsure if they are

ancestors of H. sapiens.

Hominid fossil recordHomo erectus

“Erect man”Taller (5'), had a larger

brain (~61 in3), than H. habilis.

Lived from ~1.8 million to 250,000 years ago.

Fossils from Asia: “Beijing man” and

“Java Man”.

Hominid fossil recordHomo erectus

Built crude wooden shelters, or lived in caves in groups of 20 to 50 individuals. Used flint and bone tools and cooked over fires.

Capturing and then using fire

Hominid fossil recordHomo erectus was the first hominid species to

migrate out of Africa, colonizing Asia & Europe.

Hominid fossil recordHomo neanderthalensis

In Europe, according to one view, H. erectus gave rise to Neanderthals ~300,000 years ago. They persisted there until ~35,000 years ago.

Alternatively, Neanderthals may have originated from the H. erectus that stayed in Africa and migrated out afterward.

“Out of Africa” theory

Hominid fossil recordHomo neanderthalensis (in Europe only)

Hominid fossil recordHomo neanderthalensis

The currently accepted view is that Neanderthals and modern humans share a common ancestor that lived in Africa, but that modern humans are not descended from Neanderthals.

But Europeans do have some Neander-thal genes. How?

Hominid fossil recordHomo sapiens

H. sapiens originated in Africa about 200,000 years ago. Some began to migrate out around 60,000 years ago.

Migrations of H. sapiens across the world (using mitochondrial DNA)

Hominid fossil recordHomo sapiens

The first modern humans in Europe were the Cro-Magnon men, about 43,000 years ago.

Hominid brain sizeFrom ~4 million years ago, to the present day,

brain volume in the hominid lineage has increased by a factor of 3.5:

The brain of Australopithecus had a volume of ~400 cm3; that of modern humans is ~1,400 cm3

Hominid brain sizeOld idea: our ancestors evolved a large brain to

accommodate language and use of tools.

New idea: Brain size increased due to changes in diet brought about by…

the control of fire, the domestication of plants and animals, the development and mastery of stone tools.

H. erectus campsite

Genetic vs. cultural evolutionRecent cultural evolution of Homo sapiens

Burials signify an awareness that there may be more than just this one physical existence.

Religion. philosophy

Art (painting, dance, music) are symbolic.Domestication of animals and crops allowed Man to settle and develop civilization.

Civilization fosters specialization and more culture – barter economy leads to money.Government (many varieties).

Philanthropy, democracy, communismAlso slavery, theocracy, Nazism Projects such as the space program

Genetic vs. cultural evolutionThe human state of consciousness