CH5 HOMINID FOSSILS copy

Areas of Exploration

• Hominin Evolutionary Trends

• Early Hominin Lineages and Genus Homo

• Tool Industries and Technologies

• Modeling Origins and Tracking Genomes

• Chapter Author: Lana Williams (University of Central Florida)

5.1 Hominin Evolutionary Trends

Key Objectives

• Define key terms: hominid and hominin.

• Describe anatomical changes associated with bipedalism.

Overview

• Only one species of human exists today: Homo sapiens.

• Other primates have multiple extant species (e.g., gorillas, gibbons, Old World monkeys).

• Ancestral humans lived among various ancestral species, with new species developing as adaptations occurred.

• Evidence suggests various ancestral species interbred at times.

• The paleoanthropology field studies the origins and development of early humans, emphasizing fossil records.

• Consensus: Homo sapiens shared a common ancestor with great apes ~6 - 8 million years ago.

Taxonomic Classification

• Hominids (family Hominidae) include:

  • Pongo: Orangutans

  • Gorilla: Gorillas

  • Pan: Chimpanzees and bonobos

  • Homo: Modern humans and extinct relatives

• Term hominid has evolved; originally referred to humans and closest relatives, now includes apes.

• Hominin (tribe Hominini) refers specifically to modern humans and close extinct relatives.

• Hominin evidence initially dated from 8.0 - 2.5 million years ago, with fossil records vital for understanding evolution.

Skeletal Changes and Bipedalism

Bipedalism Defined

• Bipedalism began in hominins around 7.0 million years ago.

Morphological Adaptations

• Changes in the foot, pelvis, knees, legs, vertebral column, and skull positioning.

• Walking on two legs saves energy compared to other forms of locomotion, though not for running.

Human Foot Structure

• Differences:

  • Enlarged heels to support body weight.

  • Non-opposable first toe aligned with other toes, smaller toes overall.

• Weight transference differs between human bipedal walking vs. non-human: heel to ball of foot vs. outside to middle toes in apes.

Pelvic Changes

• Larger hip joints accommodate body weight.

• Broader sacrum increases birth canal diameter.

Knee Joint Adaptation

• Enlarged knee joints support body weight, affecting energy expenditure and gait.

• Straight legs and inward bent thighs improve balance.

Vertebral Column Modifications

• Unique lumbar and thoracic bends center weight over feet.

• Foramen magnum positioning affects posture and balance.

Additional Anatomical Changes

• Reduction in tooth and jaw size, and expansion of cranial capacity.

• Early hominins had larger cranial capacities than previously observed (~320-480 cc) such as in Homo (500-900 cc).

Early Hominin Lineages and Genus Homo

Objectives

• Describe early hominin species with known dates and habitats.

• Identify key adaptations and characteristics in early hominins and genus Homo.

Hominin Diversity

• Timeline: Over 20 known extinct hominins recognized.

• Fossils shed light on lineage relationships and evolution.

Key Early Hominin Species

Sahelanthropus tchadensis

• Location: Chad, 7.0-6.0 million years ago.

• Features blend ape-like (sloping face, prominent brow ridges) and human-like (small canines, central foramen magnum).

• Diet likely consisted of plants and possibly insects.

Orrorin tugenensis

• Location: Kenya, 6.2-5.6 million years ago.

• Evidence of bipedalism inferred from femur shape; retained tree-climbing traits.

Ardipithecus kadabba

• Location: Ethiopia, 5.8-5.2 million years ago.

• Evidence of probable bipedalism from toe structure. Diet included varied plant materials.

Ardipithecus ramidus

• Location: Ethiopia, 4.4 million years ago.

• Reflects mixed traits; shell-like features suggest climbing abilities alongside bipedality.

Gracile Australopithecines

Australopithecus Speciation

• Evolved around 4.0 million years ago, played a key role in human evolution.

• Height ranged from 1.0 to 1.5 m; weight varied.

• Features generally more human-like than ape-like, showcasing bipedalism.

Robust Australopithecines

Paranthropus Genus

• Characterized by robust skulls and dentition, indicative of a herbivorous diet.

• Lived in East/South Africa (2.7 million–1.1 million years ago).

Early Genus Homo

Key Species

Homo habilis

• Location: East Africa, 2.5 to 1.4 million years ago.

• Known for significant increase in brain size and definitive tool use.

Homo erectus

• Location: Africa, Asia, Europe, 1.9 million to 400,000 years ago.

• Associated with advancements in tool-making and dietary shifts.

Archaic Genus Homo

Early Archaic Homo sapiens

• Evolved around 600,000 to 200,000 years ago, demonstrating advanced social behaviors and tool technologies.

Homo naledi

• Fossils reveal a blend of primitive and modern traits, exhibiting a transitional evolved status.

Homo neanderthalensis

• Classification remains debated; display robust adaptations and complex behaviors.

Denisovans

• Evolved across Eurasia, closely related to Neanderthals and modern humans through interbreeding.

Early Modern Homo sapiens

Evolutionary Milestones

• Anatomically modern humans exhibit significant behavioral and technological advancements; extensive cultural practices documented.

Tool Technologies

Summary of Tool Industries

• Lomekwian: Early tool use by Australopithecus (~3.3 million years ago).

• Oldowan: Characterized by choppers and flakes (2.6-1.7 million years ago).

• Acheulean: Bifacial tools (1.7 million-160,000 years ago).

• Mousterian: Neanderthal techniques (300,000-40,000 years ago).

• Aurignacian and Magdalenian: Representing modern tool sophistication and cultural development.

Genetic Modeling of Origins

Models in Population Migration

• Out of Africa Model: Proposes African origin for modern humans.

• Multiregional Continuity: Suggests simultaneous evolution in multiple regions.

• Assimilation Model: Combines aspects of both, supporting early human interbreeding with archaic populations upon migration.

Conclusion

Paleoanthropology highlights the evolutionary journey from early hominins to modern Homo sapiens, emphasizing both anatomical adaptations for bipedalism and the development of complex tool technologies that facilitated survival and cognitive growth.