Location

Ethiopia.

Species

Australopithecus afarensis.

Fossil Age

Approximately 3.2 million years old.

Significance

Oldest and most complete early human ancestor found at the time. Confirmed early bipedalism.

Key Insights

Bipedalism occurred before brain enlargement. Femur and hip structure resemble humans.

Physical Characteristics

Fully bipedal but likely climbed. Stood at 3.5 feet tall.

Chimpanzees’ arms are longer than their hind limbs with long, curved fingers adapted for climbing in trees.

Lucy’s arms were long relative to her legs, but her pelvis and knees were well-adapted for walking upright.

Humans’ pelvises, knees and feet are similar to Lucy’s. So is the way the spinal column enters the skull.

Time Period

Species/Stage

Key Features

Significance

Location

7-6 million years ago

Sahelanthropus tchadensis

Earliest known hominin
Small brain (350-400 cc)
Possibly bipedal
Flat face, large brow ridges

Represents the divergence of humans from chimpanzee ancestors

Central Africa (Chad)

6 million years ago

Orrorin tugenensis

Bipedal locomotion
Thick tooth enamel
Small teeth similar to modern humans

Provides evidence of early bipedalism

East Africa (Kenya)

4.2-3.9 million years ago

Australopithecus anamensis

Fully bipedal
Large molars
Small brain (370-400 cc)

First definitive evidence of habitual bipedalism

East Africa (Kenya, Ethiopia)

3.9-2.9 million years ago

Australopithecus afarensis

Famous fossil "Lucy"
Bipedal with some arboreal adaptations
Small brain (400-500 cc)

Important link in human evolution showcasing bipedalism and primitive cranial features

East Africa (Ethiopia, Tanzania)

2.5 million years ago

Paranthropus boisei

Robust build
Specialized teeth for chewing tough vegetation

 Small brain (450-500 cc)

Example of hominins with dietary adaptations

East Africa

2.4-1.4 million years ago

Homo habilis

First tool user (Oldowan tools)
Larger brain (500-700 cc)
Smaller teeth

Known as "Handy Man," marks the beginning of the genus Homo

East Africa

1.9 million-110,000 years ago

Homo erectus

First to use fire
Larger brain (600-1100 cc)
Robust body, long legs for walking
Acheulean tools

Spread out of Africa; "Turkana Boy" fossil showcases its adaptations for endurance running

Africa, Asia, Europe

700,000-200,000 years ago

Homo heidelbergensis

Larger brain (1100-1300 cc)
Built shelters
Advanced tools and possible hunting strategies

Ancestor of both Neanderthals and modern humans

Africa, Europe, Asia

400,000-40,000 years ago

Homo neanderthalensis

Stocky build for cold climates
Brain size similar to modern humans (1200-1750 cc)
Burials and symbolic behavior

Adapted to Ice Age Europe and developed complex tools (Mousterian culture)

Europe, Western Asia

300,000 years ago-present

Homo sapiens

Large brain (average 1350 cc)
Sophisticated tools and art
Complex social and cultural systems

Dominant hominin species with global dispersal

Originated in Africa, global

Milestone

Approx. Time

Significance

Emergence of Bipedalism

~6-4 million years ago

Freed hands for tool use, allowed long-distance travel, and better thermoregulation

Use of Tools

~2.5 million years ago

Enabled hunting, processing food, and survival in diverse environments

Control of Fire

~1.5 million years ago

Improved diet by cooking food, provided warmth, protection from predators, and fostered social bonds

Development of Language

~100,000 years ago

Enhanced communication, cultural transmission, and cooperation

Art and Symbolism

~40,000 years ago

Evidence of abstract thought, cultural development, and identity expression

Theory

Proponent(s)

Key Concepts

Strengths

Criticisms/Limitations

Theory of Inheritance of Acquired Characteristics (Lamarckism)

Jean-Baptiste Lamarck

Organisms adapt to their environment.

Acquired traits are inherited by offspring.

Early attempt to explain adaptation and evolution.

No genetic mechanism for the inheritance of acquired traits; disproven by modern genetics.

Darwin’s Theory of Natural Selection

Charles Darwin

Survival of the fittest.

Organisms with advantageous traits reproduce more successfully.

Supported by fossil evidence, biogeography, and modern genetics.

Lacks explanation of the origin of variation (addressed later by genetics).

Mutation Theory

Hugo de Vries

Sudden mutations lead to new species.

Recognized mutations as a source of variation.

Overemphasized the role of mutations while underestimating natural selection.

Synthetic Theory of Evolution (Modern Synthesis)

Julian Huxley, Theodosius Dobzhansky, Ernst Mayr, and others

Combines natural selection, genetic mutations, gene flow, and genetic drift.

Comprehensive explanation combining Darwinism with genetics; explains microevolution and macroevolution.

Limited in explaining phenomena like horizontal gene transfer or rapid evolutionary changes.

Neutral Theory of Molecular Evolution

Motoo Kimura

Most genetic changes are neutral and occur due to random drift rather than selection.

Explains molecular evolution and variation within populations.

Does not explain adaptive evolution driven by selection.

Punctuated Equilibrium

Niles Eldredge, Stephen Jay Gould

Evolution occurs in rapid bursts separated by long periods of stability.

Supported by abrupt changes in the fossil record.

Not universally observed; lacks a detailed genetic mechanism.

Endosymbiotic Theory

Lynn Margulis

Eukaryotic cells evolved through the symbiosis of prokaryotic organisms.

Supported by evidence from mitochondrial and chloroplast DNA.

Limited to explaining the origin of eukaryotic cells.

Evo-Devo (Evolutionary Development Biology)

Sean B. Carroll and others

- Evolutionary changes occur through alterations in developmental pathways.

Explains the evolution of complex structures and diverse body plans.

Still a developing field; integration with other theories is ongoing.

PRACTICE QUESTION

Q.Discuss the key stages in human evolution and their implications for understanding the origin of Homo sapiens. (150 words)