Chapter 15

HOMININ EVOLUTION

Page 565 - 619

Classification Hierarchy

Kingdom Animalia

Phylum Chordata

Class Mammalia

Order Primates

Family Hominidae

Genus Homo

Species sapiens

A MAMMAL:

Humans are Primates

• No single feature is diagnostic of a primate but, taken together the following features identify a primate:-

• Hands and feet typically have five digits that can grasp or curl objects, and thumbs and/or toes are opposable.

• Flat nails on their digits with the tips of their digits able to gain information through the sense of touch.

PRIMATES

• Large forward facing eyes that give 3D vision as well as colour because they have cones in the retinas of their eyes.

• A protective bone at the outer side of the eye socket.

• Flexible skeletons.• Large brains compared to body size.• Social animals and live in groups.• Relatively long gestation period.

Early Primates

• Prosimians (65mya)• Monkeys (35mya)• Apes (23mya)• Hominids (5mya)

EVOLUTION OF PRIMATES

PRIMATE FAMILY TREE

Crown lemur Orangutan

PRIMATE TRAITS• Common physical primate traits:

– dense hair or fur covering– warm-blooded– live young– suckle– infant dependence

• Common social primate traits:

– social life– play – observation and imitation– pecking order Common Primate Traits

Evolution of the primate

• Living primates have evolved form an ancestral species over a period 65 – 85mya.

• During primate evolution, lines that gave rise to different groups of modern primates diverged at various times.

• It is estimated that the line that led to modern humans diverged from the line that led to modern chimps about 5 – 7 mya.

• Times of divergence are estimated using DNA sequences.

EVOLUTION OF PRIMATES

• The evolution of primates is characterized by trends towards:

– mobile limbs– grasping hands (with opposable thumbs)– a flattened face – binocular vision– a large, complex brain (for learned behavior)– a reduced reproductive rate

PRIMATE 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 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

New World MonkeysHOMINOIDS

Primate Family Tree

Crown lemur Orangutan

Pre-Hominin Evolution

• Ardipithecus ramidus 4.4 - ? mya• A. anamensis 4.2 - 3.9• A. afarensis 4.2 - 2.5• A. bahrelghazali 3.5 - 3.0• A. africanus 3.5 - 2.5• P. aethiopicus 2.7 - 2.3• A. garhi 2.5 - ?• P. boisei 2.3 - 1.3• P. robustus 2.0 - 1.0

• Bipedalism• Tools• Language

Reconstruction of Australopithecine

Hominoid (Man/ Apes) Evolution

• Proconsul is believed ancestral to hominins.

Humans are hominoid

Humans are hominins

• Modern classification places the humans in the taxonomic group known as the tribe Hominini, that is humans are hominins.

• It is only at this level of classification that humans are separated from all other great apes.

Classifications can change

• Prior to 1980 the accepted classification scheme identified humans as the only member of the family Hominidae.

• The classification was based on comparative anatomy and physiology.

• Molecular analysis has identified a much closer relationship between humans and other great apes.

What is a hominin?

• In the past the term ‘hominid’ referred to humans and their erect-walking ancestors.

• Hominin is now the preferred term that refers to this group.

• The only living hominin species is the modern human, Homo sapiens.

• Hominins both living and extinct are distinguished by their ability to walk upright.

Where did the human evolution begin?

• In the 19th century fossils showed the origin was in Africa. See table 15.3 (pg 582).

Time Distribution.• No fossil eveidence of hominins of the genus

Homo before 2.4mya.

• Fossils of hominins, such as Ardipithecus and Australopithecus appeared millions of years before Homo.

• When the time distribution of one group occurs after that of the second group, the later group cannot be ancestral to the earlier group.

• When the time distributions of two species coincide, they cannot have an ancestor-descendant relationship, eg. H.habilis and A.robustus.

Australopithecus

• Two forms of the genus: graciles and robusts.

• Table 15.5 show the different species in the genus

• Australopithecus. The robusts are placed by some scientists into another genus, Paranthropus.

• This means that Australopithecus robustus is sometimes called Paranthropus robustus.

Gracile australopiths

• Several lines of evidence, including their jaw and teeth structure, support the conclusion that the graciles could be ancestral to the first Homo species.

Robust australopiths• Robust australopithians have

heavy built skulls, heavy brow ridges, very large molar teeth, and in males a bony crest on the top of the skull.

Australopithecus vs. Modern

Australopithecus, 4-3 myrs ago Modern human

Chimpanzee

Changes in the skull in the evolution of modern humans

• Recognizable changes in the skull which occurred during the evolution of modern humans include:

– Change in the arrangement of the teeth, from the rectangular arrangement of the apes to a parabolic shape in hominids, loss of the gap between front and back teeth.

– Reduction in the size of the front teeth, especially the canines.

Cranial Comparisons

H. neanderthalensis Homo ergaster Homo Sapiens

Cranial Comparisons

• Loss of the large bony ridges (supraorbital ridges) above the eyes.

• Larger brain size.

• Flatter faces.

Cranial Comparisons

SEXUAL DIMORPHISM IN AUSTRALOPITHS

• Sexual dimorphism - where differences exist between the adult males and females in average height, body mass, or other features.

How did early hominins live?

• Social organisation – group of related males who control and defend a group of females.

• Inferring diets – relative size of teeth, microscopic examination of tooth wear, jaw size and jaw musculature.

• Waistline – digestive tracts of herbivores are much longer than carnivores.

How did early hominins live?

• Habitat – examining fossils of plants and animals found in association with australopithecine fossils give us an idea what type of habitat was inferred.

• Other evidence of habitat includes analysis of pollen.

• Presence of water animals and plants indicate the presence of water.

MODE OF LOCOMOTION

• Although australopithecenes are capable of bipedal it would not be the same as humans today.

• Also show adaptations to tree climbing.

• The early hominins would have walked erect, however retreated to the trees at night.

• Culture – basic tools used as well as sticks.

Evolutionary relationships

THE GENUS HOMO

Early homo species were different :

- reduction in size of teeth- increase in brain size.

It is reasonable to hypothesise that

increasing brain size resulted from natural

selection favouring greater intelligence.

• The earliest human species is generally accepted as Homo habilis.

• The genus Homo also includes H.erectus, H.heidlebergensis, H.neanderthalensis, and H.sapiens.

• Scientists often disagree with the number of species, which is a reminder that even if they examine the same fossil material, scientists may differ in their interpretation and conclusions.

CURRENT VIEW

• Fossil discoveries support a multi-branched human evolutionary line.

Q. phyletic or branching evolution?

• About 10,000 to 12,000 years ago evidence of agricultural practices first appeared in the Middle East.

• Nomadic lifestyles involved small groups of cooperative hunter-gatherers.

• Sedentary lifestyles involved food production through domestication of animals and cultivation of wild plants.

• Increased population size is related to a sedentary lifestyle.

HUMAN BIOLOGICAL EVOLUTION

• Biological Evolution describes the changes in human population that have resulted from natural selection acting over generations on inherited phenotypes and producing differential survival and reproduction under a particular set of environmental conditions.

• Genetic diversity exists in human populations, both discrete polymorphisms and clinal graduations.

• • Biological evolution, cultural change and

technological evolution interact.

• Cultural change in many ways is based on technological evolution.

• Technology extends human capabilities.

• With the appearance of Cro-Magnons, – human evolution has become almost

entirely cultural rather than biological

• Humans have spread throughout the world – by devising means to deal with a broad

range of environmental conditions

Cultural Evolution

Cultural Evolution • Cultural evolution is the term used to refer to changes in the human way

of life since the evolution of biologically modern humans. Human cultural evolution has been driven by three major advances:

The development of nomadic hunter gatherer societies in which knowledge about the environment, seasons, food and social traditions are passed from generation to generation.

The development of agricultural societies in which production of food no longer involves the whole population, freeing the society to develop arts, writing, music, crafts, mathematics and other areas of knowledge. Food supplies are more reliable than in hunter/gatherer societies too.

The development of technological societies, which began with the Industrial Revolution of the 18th century. This development has led to greater urbanization, specialization of roles in society and rapid technological change.

Human influences on evolution• Human intervention has influenced the evolution of

our own and other species on earth in a number of ways:

The expansion of human populations and industries, and the resulting loss of habitat, has caused the extinction of many species.

Old and new technologies are altering the gene pools of domesticated species of animals and plants.

Screening techniques and treatments are becoming available for a range of genetic diseases.

• Chapter Review pages 618 and 619