Unit 3 - Modern Human Origins

Homo habilis

First clear member of our genus; appears 2.5 mya with tools distinct from australopithecines and sets stage for Homo erectus and modern humans.

Homo erectus dispersal

By 1.8 mya fossils and tools appear outside Africa; first hominin to reach Europe and Asia.

Middle Pleistocene "Muddle in the Middle"

Period where isolated Homo populations evolved regionally, raising questions about whether modern humans came from one lineage or multiple.

Regional Middle Pleistocene Lineages

Europe had Neanderthals, Asia had H. erectus and Denisovans, Africa had H. heidelbergensis and early H. sapiens.

Braided Stream Model

Human evolution was not linear but consisted of branching, reconnecting lineages with gene flow.

Pit of Bones (Sima de los Huesos)

Site in Spain with 7,000+ fossils of 28 individuals (~400kya), likely Homo heidelbergensis; possible intentional body deposition.

Retromolar Gap

Space behind the last molar characteristic of Neanderthals, rare in modern humans.

Midfacial Prognathism

Forward projection of midface in Neanderthals, possibly adapted for warming/humidifying cold air.

Occipital Bun

Posterior skull projection unique to Neanderthals.

Homo neanderthalensis

Species from Europe and western Asia; 1500 cc brain, large nasal opening, strong brow ridge, long low cranium, and cold-adapted body.

Neanderthal Incisor Wear

Beveled wear from gripping materials like hides or fibers with front teeth.

Neanderthal Barrel Chest

Large thorax and lungs for high oxygen intake in Ice Age conditions.

Neanderthal Limb Proportions

Short distal limb segments following Allen's Rule to reduce heat loss.

Autapomorphy

Trait unique to a single species or lineage.

Neanderthal Burials

Evidence suggests intentional burial and complex behavior.

Neanderthal Cave Structures

Circular constructions made from broken stalagmites requiring planning and controlled fire.

Neanderthal Symbolism

Perforated shells, red pigment, and ochre ornaments in Spain suggest symbolic behavior before modern humans arrived.

Neanderthal Behavioral Summary

Used tools similar to humans, had flexible diet, possible symbolic behavior, possible burials.

Neanderthal Disappearance

Disappeared ~40kya; last populations in Iberian Peninsula.

Neanderthal Decline Causes

Demographics, climate instability, competition with expanding modern humans, and partial genetic absorption.

Neanderthal DNA in Modern Humans

Non-African humans carry 1-2% Neanderthal DNA.

Assimilation Model

Modern humans emerged in Africa but interbred with regional archaic populations during expansion.

Denisovans

Extinct hominins known mainly from DNA; diverged from humans/Neanderthals, split from Neanderthals ~300kya, widespread in Asia.

Denisovan Genetic Legacy

Multiple populations existed; some regionally adapted; interbreeding with both Neanderthals and early modern humans occurred.

Homo heidelbergensis (Africa)

600-200kya; widely distributed in Africa; 1200 cc brain, thick brow ridge, rounded cranium; transitional species toward modern humans.

Anatomically Modern Homo sapiens

Appear ~300kya in Africa; 1300 cc brain, vertical forehead, reduced prognathism, chin present, reduced brow ridge.

AMHS Out of Africa

Earliest evidence outside Africa ~100kya in Israel; overlapped with Neanderthals in the Near East.

mtDNA

Mitochondrial DNA inherited maternally; high mutation rate; useful for tracing direct maternal lineages and ancient migrations.

Mitochondrial Eve

Most recent common maternal ancestor of all humans; lived 100-200kya in Africa.

Y-Chromosome Adam

Most recent paternal ancestor; lived 200-300kya in Africa; not contemporaneous with Mitochondrial Eve.

Haplogroups

Genetic lineages defined by shared mutations on mtDNA or Y-chromosome; trace descent and migrations.

Haplogroup C1b2b

Ancient lineage linked to Aboriginal Australians.

Haplogroup B2

Associated with coastal migrations; common in western Americas.

Genetic Diversity in Humans

Low compared to other species; supports recent African origin and population bottlenecks.

African Genetic Diversity

Highest in African populations because they are oldest and have accumulated mutations longest.

Neanderthal mtDNA

Falls outside modern human variation, indicating long separate evolution.

Cro-Magnon mtDNA

Falls within modern human variation, showing continuity with AMHS.

Neanderthal-Denisovan Hybrid "Denny"

13-year-old individual showing direct interbreeding between Neanderthals and Denisovans.

Flores, Indonesia

Key site east of Wallace's Line; stone tools ~800kya likely made by Homo erectus.

Island Rule (Dwarfism/Gigantism)

Large animals shrink, small animals grow on islands; seen in elephants and rats on Flores.

Homo floresiensis

3'6" tall, 55 lbs, 380 cc brain; lived until ~50kya; evolved via island dwarfism; highly debated species.

Homo luzonensis

Small-bodied hominin from the Philippines; suggests complex island evolution.

Homo naledi

Small-brained hominin from South Africa; shows multiple hominins coexisted recently.

Multiple Hominins Over 4 Million Years

Several species coexisted at the same time, including Homo erectus and Paranthropus.