Chapter 4

Human Evolution

Chapter Outline

Macroeveolution and the Process of Speciation

Mammalian Primate Evolution Human Evolution The Upper Paleolithic The Modern Human Origins Debate

Macroevolution and the Process Of Speciation

Macroevolution focuses upon the formation of new species (speciation) and on the evolutionary relationships between groups of species. Speciation can occur as a result of cladogenesis or anagenesis.

A species is usually defined as a population or group of populations capable of interbreeding and producing fertile offspring.

Speciation Speciation is inferred in the fossil record

when a group of organisms takes on a different appearance over time.

Over time, as the two populations come to differ from each other, speciation occurs in a branching fashion known as cladogenesis.

In anagenesis a single population accumulates new mutations over time until it is considered a separate species.

Speciation

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Punctuated Equilibria

A model of macroevolutionary change that suggests evolution occurs via long periods of stability or stasis punctuated by periods of rapid change.

Mammalian Primate Evolution

Climate changes led to the appearance of primates about 65 million years ago.

These were small, arboreal, nocturnal, insect eaters.

About 23 million years ago, hominoids, the primates that include all living and extinct apes and humans began to appear in Asia, Africa, and Europe.

Genetic studies have confirmed that the African apes are our closest living relatives.

Bipedalism preceded brain expansion and played a pivotal role in setting us apart from the apes.

Continental Drift

According to the theory of plate tectonics, the movement of continents embedded in underlying plates on the earth’s surface in relation to one another over the history of life on earth.

Continental Drift

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Human Evolution Humans and their ancestors are distinct

among hominoids for bipedalism, a form of locomotion on two feet.

In the past 30 years, studies have confirmed that the African apes (chimpanzees, bonobos, and gorillas) are our closest living relatives.

Between 8 and 5 million years ago, humans, chimpanzees, and gorillas began to follow separate evolutionary courses.

Changes in Anatomy Associated with Bipedalism

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Australopithecines

The genus including several species of early bipeds from southern and eastern Africa living between about 4.3 and 1.1 million years ago, one of whom was directly ancestral to humans.

Robust Australopithecines

Several species within the genus Australopithecus, who lived from 2.5 and 1.1 million years ago in eastern and southern Africa.

Known for the rugged nature of their chewing apparatus (large back teeth, large chewing muscles, and bony ridge on their skull tops for the insertion of these large muscles).

Robust Australopithecines had large molars and a bony ridge on top of their skulls.

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Gracile Australopithecines

Members of the genus Australopithecus possessing a more lightly built chewing apparatus.

Likely had a diet that included more meat than that of the robust australopithecines.

Homo habilis

“Handy man.” The first fossil members of the genus

Homo appearing 2.5 million years ago, with larger brains and smaller faces than australopithecines.

May have been a tertiary scavenger.

Oldowan

The first stone tool industry. Beginning between 2.6 and 2.5 million

years ago.

Oldowan Tools

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Lower Paleolithic

Old Stone Age beginning with the earliest Oldowan tools.

Spanning from about 2.6 million to 250,000 or 200,000 years ago.

Homo erectus “Upright man.” A species within the genus Homo first

appearing just after 2 million years ago in Africa and spreading through the Old World.

Had a brain close in size to that of modern humans.

Had sophisticated behaviors including use of fire for warmth, cooking, and protection.

Made smaller and lighter tools

Homo sapiens

Between 400,000 and 200,000 years ago, evolving humans achieved the brain capacity of contemporary Homo sapiens.

Several variations of the genus Homo existed around this time, including the Neandertals.

Neandertal

A distinct group within the genus Homo inhabiting Europe and Southwest Asia from approximately 125,000 to 30,000 years ago.

Represented as the classic “cave men.” They had modern-sized brains with faces

and skulls that were very different from later fossilized remains.

Associated with the Mousterian tool industry.

Neandertal Culture

The use of fire was essential to their survival in cold climates.

They lived in small bands or family units, in the open and in caves.

They likely used language to communicate. They buried their dead, reflecting ritual

behavior. Fossil remains of an amputee discovered in

Iraq and an arthritic man excavated in France imply they cared for the disabled.

Mousterian

The tool industry of the Neandertals and their contemporaries of Europe, Southwest Asia, and northern Africa from 125,000 to 40,000 years ago.

Mousterian tools are lighter and smaller than those of earlier traditions.

Previous industries obtained only two or three flakes from an entire stone core, Mousterian toolmakers obtained many smaller flakes, which they retouched and sharpened.

Homo sapiens

Evidence indicates that at least one population of archaic H. sapiens evolved into modern humans.

Whether this was due to the biological evolution of a new species or a simultaneous worldwide process involving all archaic forms is debated.

Upper Paleolithic

The last part (40,000 to 10,000 years ago) of the Old Stone Age, featuring tool industries characterized by long slim blades and an explosion of creative symbolic forms.

The Multiregional Hypothesis

The hypothesis that modern humans originated through a process of simultaneous local transition from Homo erectus to Homo sapiens throughout the inhabited world.

Recent African Origins Hypothesis

The hypothesis that all modern people are derived from a single population of archaic H. sapiens from Africa.

These H. sapiens replaced other archaic forms due to superior cultural capabilities.

Also called the “Eve” or “Out of Africa” hypothesis.