Human Evolution

Unit 4: Human Evolution

Primate Evolution

The study of human evolution begins with an examination of primates, focusing on key contributions and historical debates surrounding the understanding of human origins. One of the earliest proponents of the idea that humans share a common ancestry with apes was Thomas Huxley. In his 1863 work titled "Evidence on Man's Place in Nature," Huxley argued for the relationship between humans and certain primates, particularly the apes.

Historical Context

Despite Huxley’s groundbreaking work, he faced significant opposition, notably from Samuel Wilberforce, known as “Soapy Sam,” who was the Bishop of Winchester. Their famous debate in 1860 at Oxford highlighted the contentious atmosphere surrounding evolutionary theory at the time.

Evidence of Man’s Place in Nature

In his examination, Huxley compared skeletons of various primates and humans, illustrating anatomical similarities and establishing a framework for understanding evolutionary relationships.

Anatomical Comparisons

Huxley provided diagrams and photographs of skeletons from species such as:

  • Gibbons

  • Chimpanzees

  • Gorillas

  • Orangutans

  • Humans
    Note: The diagrams were drawn from specimens housed in the Museum of the Royal College of Surgeons.

Molecular Evidence

Two researchers, Sarich and Wilson (late 1960s), further advanced the study of human evolution through molecular evidence. They focused on the albumins (a type of protein) found in the serum of apes and humans.

Findings and Methodology

Their method included:

  • Quantitative micro-complement fixation method to compare serum albumin among apes and humans, confirming close immunological resemblances.

  • They concluded that apes and humans have a more recent common ancestor than previously thought, suggesting divergence as recent as 4 to 5 million years ago.

Key Results

  1. Common Ancestry Hypothesis: It was found that if humans and Old World monkeys shared a common ancestor 30 million years ago, then humans and African apes diverged around 5 million years ago in the Pliocene era.

  2. Evolutionary Clock: The evolutionary changes in hemoglobin and albumin were noted to occur at a consistent rate across different lineages, allowing for the establishment of a molecular evolutionary clock.

  3. The close immunological relationship between human serum and that of African apes (particularly gorillas and chimpanzees) was emphasized, showing significant reactivity in immunological tests.

Classification of Modern Primates

Modern primates can be classified into four broad types:

  1. New World monkeys

  2. Lemurs

  3. Old World monkeys

  4. Apes

Evolution of Primates

Timeline of Primate Evolution

  1. Primatomorpha - The grouping of primates began approximately 90-65 million years ago.

  2. Classification of primates can be delineated into:

    • Wet-nosed primates: Includes lemurs and lorises, diverging earlier in the timeline.

    • Dry-nosed primates: Includes tarsiers and simian monkeys.

    • Eventually leading to New World monkeys and Catarrhini, which includes Old World monkeys and apes.

The Hominidae Family

Definition and Scope

  • The Hominidae family encompasses all living and extinct ape and human species.

  • The term hominin is employed to refer to humans and all human-like ancestors starting from 1871.

Hominid and Hominin Evolution

A significant aspect of understanding human evolution is the timeline based on fossil evidence and genetic studies.

Split from Chimpanzees

The divergence of the human lineage from chimpanzees is one of the key events:

  • Candidates of Homininae include:

    • Kenyapithecus: From Kenya, 16-14 million years ago.

    • Griphopithecus: Found in central Europe and Turkey, 16-14 million years ago.

    • Dryopithecus: West/Central Europe, dated to 13-8 million years ago.

    • Sivapithecus: From India, dating back to 12 million years ago.

    • Ouranopithecus: Located in Greece, dated back 9 million years ago.

    • Samburupithecus: Discovered in Northern Kenya, 9 million years ago.

    • Sahelanthropus: From Chad, dating 7-6 million years ago.

    • Orrorin: Found in Central Kenya, dated to 6 million years ago.

Genus Ardipithecus

  • The Ardipithecus genus dates back to 4.4 million years ago and signifies critical evolutionary traits.

  • Human and chimpanzee divergence has been suggested to occur between 7 and 4 million years ago.

Australopithecus

Noteworthy Species

Australopithecus, particularly A. afarensis, is significant due to key fossil discoveries:

  • The famous skeleton known as "Lucy" was found in Ethiopia, dating to about 3.2 million years ago, providing crucial insights into early hominins.

Evolution of Genus Homo

Emergence of Early Homos

  • Homo habilis is recognized as the earliest representative, evolving around 2.8 million years ago, marking the onset of tool-making behavior.

  • Homo erectus evolved approximately 2 million years ago, showcasing more modern body proportions and further tool usage, particularly for hunting.

Migration Patterns

The evolution and migration of humans also present important aspects:

  • Two theories regarding migration: Multiregional and Out of Africa.

  • Homo sapiens began migrating out of Africa around 100,000 years ago, while Homo erectus migrated as early as 1.5-1.8 million years ago.

The Evolutionary Branches

The chart detailing the evolution of the genus Homo notes various species over time, including Neanderthals, Denisovans, and others leading to modern Homo sapiens.