human evolution

Human Evolution

Relationship to Primates

• Phylogeny suggested by Thomas Huxley, 1863

• Outline Areas of Study:

  • Relationship between humans and primates

  • Relationships among humans and apes

  • The recent ancestry of humans (genus Homo)

Our Relationship to Primates

• Homologies: Physical similarities between humans and primates.

  • Forward facing eyes: Indicates depth perception.

  • Feet: Adaptations for different locomotion styles.

  • Gripping thumbs: Ability to grasp and manipulate objects effectively.

  • Coccyx: Vestigial tail structure in humans.

  • True tail: Present in some primate relatives.

Molecular Evidence of Relationship to Primates

• Study referenced: Reis et al. (2018) explored genomic data among primates.

• Methodology: Analyzed genomes of nine primate species and DNA samples from 358 others.

• Findings:

  • Primates form a monophyletic clade that diverged from other mammals.

  • Humans share many genetic similarities with primates, indicating deep nesting within the primate clade.

Phylogeny of the Apes

• Old World Monkeys (e.g., Rhesus monkey) and Great Apes:

  • Bonobo, Common Chimpanzee, Pygmy Chimpanzee, Orangutan, Gorilla, Human.

  • Ape Characteristics:

  • Large brains

  • No tail

  • Erect posture

Great Ape Traits

• Hominidae Family (Great Apes):

  • Enlarged ovaries

  • Enlarged mammary glands

  • Flattened fingernails

  • 32 teeth

  • Prolonged parental care

Phylogeny of African Great Apes

• All phylogenetic trees based on molecular data support relationship.

• Divergence of hominin lineage from chimpanzees and bonobos estimated between 7.3 and 8.4 million years ago.

Recent Ancestry of Humans

• Common Ancestor of Chimpanzees and Humans existed around 7 million years ago.

• Traits likely present in the common ancestor:

  • Broad, fruit-based diet

  • Use of tools

  • Hunting culture

  • Knuckle-walking

Hominin Innovations and Evolution

• Hominin: Any species related more closely to humans than to chimpanzees.

• Three Major Innovations in the Hominin Line:

  • Big brains

  • Bipedalism: Evidence suggests gradual evolution of bipedal traits.

  • Tool use: Associated with the evolution of larger brains.

• Earliest Fossils: Suggest bipedalism emerged around 7 million years ago.

Clues to Bipedalism

• Foramen magnum orientation reveals locomotion changes:

  • In Sahelanthropus, the foramen magnum was oriented vertically, indicative of upright walking.

  • Orrorin tugenensis showed femur adaptations suitable for bipedalism.

  • Ardipithecus ramidus had short fingers suitable for tool use but retained some tree-climbing adaptations.

Australopithecus and Bipedalism

• Australopithecines (generally spanning from 4.2 million to 1 million years ago):

  • More efficient walkers than Ardi.

  • Adaptations for both walking on ground and climbing.

• Evidence of Bipedalism:

  • Footprints in Tanzanian volcanic ash, indicating a gait similar to modern humans.

Evolution of Bipedalism

• Driven by environmental factors:

  • Climate change in the late Miocene altered habitats leading to the fragmentation of forests.

  • An upright gait allowed more efficient travel between tree resources and conservation of energy.

  • Another hypothesis considers bipedalism as an adaptation for thermoregulation against sunlight exposure.

Megadont Hominins and Dietary Adaptations

• Early hominins evolved larger, flatter molars adapted for eating seeds and nuts instead of fruit and leaves.

• Paranthropus robustus and P. bosei showcased adaptations conducive to powerful chewing.

Homo Habilis (Handy Man) and Tool Use

• First known toolmaker dating back approximately 1.75 million years ago.

• Discovery of simple stone tools associated with Homo habilis fossils indicates linkage between tool use and genus evolution.

• Evidence suggests stone tools can date to 3.3 million years ago, earlier than Homo habilis.

Homo Erectus

• Period: 1.89 million to 110,000 years ago.

• Evolutionary traits:

  • Modern human-like body proportions; elongated legs and shorter arms, with a larger braincase.

  • Fossil discoveries emphasize the diversity within early Homo.

  • Notable find: Turkana Boy, dated around 1.6 million years.

Homo Naledi

• Period: 335,000 - 236,000 years ago.

• Displays mix of primitive traits (small brain, curved fingers) and modern characteristics (hands and feet resembling both Neanderthals and modern humans).

Migration of Homo Erectus

• Expanded from Africa approximately 1.9 million years ago.

• Fossils discovered in Indonesia and Georgia indicating adaptation diversity and evolutionary expansions beyond Africa.

Homo Floresiensis

• Discovered in 2004 in Flores, Indonesia; dated 100,000 - 50,000 years ago.

• Standing only 100 cm tall, the cranial capacity was merely 417 cc.

• Questions surrounding their lineage suggest they might be more closely related to H. habilis rather than H. erectus.

Parallel Humans: Homo Heidelbergenesis and Neanderthals

• Homo Heidelbergenesis dated 700,000 - 200,000 years ago with advanced tool use (e.g., Levallois tools).

• Neanderthals existed from 400,000 to 40,000 years ago; notable for their large brain size and rich culture involving tools and symbolic expressions.

• Evidence suggests cognitive complexities in cultural practices among Neanderthals.

Evolution of Homo Sapiens

• Fossils of early Homo sapiens date back 300,000 years, with a distinctive skeletal build.

• Evolution of H. sapiens encompassed expanding tool diversity and expressions of abstract thought (e.g., jewelry, cave art) by 40,000 years ago.

Inbreeding and Migration of Early Humans

• Genetic studies highlight early human migrations out of Africa and interbreeding with Neanderthals and Denisovans, providing insights into modern human genetics.

The Evolution of the Human Brain

• Hominin brain size has tripled over four million years, linking anatomical changes with advancements in cognition and tool use.

• The evolution of the brain reflects complex interrelations between neurology and social behaviors, critical for survival in various environments.