Neanderthal and Human Evolution

Neandertal Ontogenetic Development

• When addressing questions of cognitive modernity, ontogenetic differences between modern humans and Neandertals can be examined.
• Areas of focus:
  • Dental development
  • Brain development
• Two competing hypotheses:
  • Neandertals matured more quickly than modern humans, resulting in shorter childhoods.
  • Neandertals and humans matured at a similar rate, leading to similar childhood lengths.

Dental Development and Eruption

• Dental development and eruption timings at various ages (Birth, 6 months, 1 year, 2 years, 4 years, 6 years, 8 years, 10 years, 12 years, 15 years, 21 years).
• Reference: Buikstra, J.E. & Ubelaker, D.H. (1994).

Neandertal Cranial Anatomy

• Key Features:
  • Large, shovel-shaped incisors, often heavily worn.
  • Robust, double-arched browridges.
  • Inflated cheeks (no canine fossa).
  • High, wide, and large nasal aperture (nose).
  • Midfacial projection.
  • Long and low vault.
  • Large cranial capacity.
  • Large juxtamastoid eminence.
  • Occipital bun.
  • Retromolar space.
  • No chin.

Modern Human Cranial Anatomy

• Key Features:
  • Large spherical (globular) cranium (average cranial capacity = $1400 cm^3$).
  • Small brow ridges.
  • Vertical forehead.
  • Small orthognathic face.
  • Projecting chin (mental eminence).
  • Rounded occipital.
  • Smaller, delicate body build combined with large brain size.
  • Canine fossa, no retromolar gap.

Modern Human Development

• Most brain development occurs after birth (only 28% of ultimate size at birth).
• Brain size then develops rapidly but reaches adult size later than other primates.
• Highly dependent – ‘secondarily altricial’.
• Prolonged development has important effects on internal brain structures.
• Interaction and stimulation from enriched physical and cultural environment alters ‘wiring’ with greater stimulation.

Brain Size and Ontogeny

• Neandertals and humans have similar brain size and shape at birth (elongated cranial shape; approx. $400cc$).
• Neandertals have similar level of altriciality at birth as humans.
• Globularization phase in humans begins with eruption of deciduous dentition.
• Bulging at parietals; enlarged cerebellum (Hublin et al. 2015).

Humans vs. Neandertal Development Findings

• Human temporal lobes (language, memory, social function) are larger than in Neandertals.
• Studies of timing of development from Neandertal juveniles suggest dental development occurred faster in Neandertals than modern humans (enamel microstructure).
• And/Or some phases of somatic development were accelerated compared to modern humans.
• Neandertals reached reproductive periods earlier than modern humans.

DNA Evidence for Brain Development

• “less cognitively adept” (Blangero 2015)
• Several of the identified genes that differ between Neandertals and modern humans are involved in brain development and function.
• Gene expression not always known.
• Genes modified in humans that may influence the number of neurons:
  • CASC5, KIF18A, TKTL1, SPAG5, VCAM1
• Neandertals had less grey matter surface area of the brain.
  • Helps process information in the brain
• And less white matter.
  • Reduced brain connectivity
• Other key regions of the brain were smaller in Neandertals:
  • Broca’s area - language
  • Amygdala – emotion and motivation

Neandertal Minds

• Did the ontogenetic differences lead to two different minds?
• What was the ‘Neandertal mind’?
• “something intangibly different between Neandertals and humans”
• How did the ‘modern mind’ emerge?
• “We know next to nothing about Neandertal cognition from genetics, because we know next to nothing about human cognition from genetics” – John Hawkes

Long-Term Working Memory

• Long-Term Working Memory (Expert Mind)
  • Chess players, musicians
  • Ability to store a skillset
  • Ability to replay motor behaviors
  • Does not fade quickly
  • Linked to executive functions of the frontal lobe
  • Levallois Industry
• “Enhanced” Working Memory
  • Allows for innovation

Emergence of Homo sapiens

• DNA of Neandertal, H. sapiens, and Denisovans in a moment…
• And whatever happened to the Neandertals…? And what their extinction related to us and our intelligence…or something else?

Chronology

• Paleolithic – Europe
  • Lower Paleolithic
    • $3.4 mya – 300 ka$
  • Middle Paleolithic
    • $300 – 45 ka$
  • Upper Paleolithic
    • $45 – 10 ka$
• Stone Age – Africa
  • Early Stone Age
    • $3.4 mya – 300 ka$
  • Middle Stone Age
    • $300 – 45 ka$
  • Late Stone Age
    • $45 – 10 ka$

Transitions of the Middle Pleistocene

• Evolutionary transitions did not just take place in Europe.
• The transition to H. sapiens was taking place in Africa.
• How to classify these transitional groups…?
• Emergence models: Multiregional Hypothesis (MH) or Replacement Hypothesis (RH)?
• RH models are supported by both the fossil and DNA evidence.
• Emergence of modern humans in Africa.
• Dispersal to Europe and Asia afterwards.
• Several limited episodes of hybridization between modern humans and local populations.
• Possibly selection against Neandertal/Denisovan genes?

Multi-Regional Models

• Standard – long-term gene flow between “species” over long distances leads to evolution of AMHS simultaneously everywhere.
• Modified – AMHS evolved in Africa, then assimilated populations outside of Africa.

Replacement Models

• “Out of Africa”: AMHS evolved in Africa, then dispersed and replaced all other species.
• Weak replacement / hybridization: AMHS evolved in Africa, then dispersed, hybridized, and replaced others.

Emergence of Modern Humans

• Locations and dates:
  • Jebel Irhoud, Morocco - $300,000$
  • Ndutu, Tanzania - $400,000$
  • Omo Kibish, Ethiopia - $195,000$
  • Bodo, Ethiopia - $600,000$
  • Herto, Ethiopia - $160,000$
  • Ngaloba, Tanzania - $120,000$
  • Kabwe/Broken Hill, Zambia - $125,000$
  • Florisbad, South Africa - $260,000$
  • Rising Star, South Africa - $235,000$

Transitional Forms in Africa

• Archaic sapiens Grade
  • Grades – reflecting the different stages of evolutionary transition (rather than species designation).
  • Many have been classified as H. heidelbergensis or merely ‘transitional’.

Jebel Irhoud

• Morocco, $300 ka$
  • Modern human face
  • Slightly elongated cranial vault
  • Chin…

Comparison of Late Homo Species Crania

• Neanderthal:
  • Double-arched browridge
  • Large and projecting nasal cavity
  • Face retracted under braincase
• Modern Human:
  • Delicate cheekbones
  • Relatively broader face
  • Lower and smaller braincase
  • Globular braincase

Modern Human Cranial Anatomy

• Large spherical (globular) cranium (average cranial capacity = $1400 cm^3$).
• Small brow ridges.
• Vertical forehead.
• Small orthognathic face.
• Projecting chin (mental eminence).
• Rounded occipital.
• Smaller, delicate body build combined with large brain size.
• Canine fossa no retromolar gap.

Comparison of Neandertal and Anatomically Modern Human

• Illustrative comparison of Neandertal and anatomically modern human features.

Human Chin

• The Human Chin – Adaptation or Byproduct?
• Long debated, no consensus
• Selection related to:
  • Chewing stress
  • Speech
  • Sexual ornamentation
  • Or by product of selection for other traits in the mandible or teeth
  • Or a product of genetic drift

Bergmann's and Allen's Rules

• Neanderthal:
  • long, low braincase
  • broad nasal aperture
  • broad hips (pelvis) and trunk
  • short forearm
  • extremely robust hand bones
  • large joint surfaces
  • long lower leg
• Modern Human:
  • short, high braincase
  • narrow nasal aperture
  • narrow hips (pelvis) and trunk
  • long forearm
  • less robust hand bones
  • smaller joint surfaces
  • short lower leg

Modern Human Body Plan

• What is the Modern Human Body Plan? (and did it give us advantages over Neandertals?)
  • Long distance running (Endurance Running ER)
  • Humans outrun many animals at long distances
  • Our body plan is set up to stabilize during running
  • Sweating makes long distance running possible
  • “Are We Born to Run?”
  • “Could Neandertals Run?”
  • Throwing
  • Homo erectus shoulder was too inflexible to throw well with narrow shoulders, short clavicle and anteriorly placed glenoid fossa
  • Humans with wide shoulders, long clavicle and dorsal scapula with lateral glenoid fossa
  • High degree of humeral torsion compared to other primates and hominins
  • Expanded range of motion
  • Selection for throwin…or happy by-product of alteration of thorax shape for endurance running

Throwing

• Maximum shoulder rotation (middle) is when elastic energy is able to power the throw
• NEIL ROACH

Anatomically Modern Homo sapiens (AMHS)

• $300 ka$ - present!
• There are a number of hominins running around the landscape at the beginning of this period.
• Where did AMHS come from? 2 models:
  1. Multiregional
  2. Replacement
• Jebel Irhoud, $300 ka$

Multi-regional Models

• Standard – long-term gene flow between “species” over long distances leads to evolution of AMHS simultaneously everywhere.
• Modified – AMHS evolved in Africa, then assimilated populations outside of Africa

Replacement Models

• “Out of Africa”: AMHS evolved in Africa, then dispersed and replaced all other species.
• Weak replacement / hybridization: AMHS evolved in Africa, then dispersed, hybridized, and replaced others (minimal contribution to modern humans from other hominins)

Climate evidence and Replacement Model

• Climate evidence fits replacement idea
  • During glaciations
    • Europe and Africa were isolated
    • Difficult to maintain gene flow under such conditions
  • As world became warmer, hominins migrated from Africa into Eurasia
    • Example of glacial period
    • Example of interglacial period

Out-of-Africa Model Predictions

1. AMH fossils oldest in Africa; should appear later elsewhere
2. Transitional forms only in Africa
3. Coexistence of archaic & modern humans outside Africa
4. Africa should show greatest genetic diversity because humans have been there longest
5. Modern human behavior should originate in Africa

Earliest Evidence of Modern Humans by Region

• Jebel Ihroud, Morocco, $300 ka$
• Omo 1, Ethiopia, $195 ka$
• Klasies, S. Africa, $120-70 ka$
• Misliya, Israel, $200ka$
• Al Wusta, Arabian peninsula $86 ka$
• Madjedbebe? and Lake Mungo, Australia $65 ka$
• Tam Pa Ling, Laos $48ka (70?) ka$
• Niah Cave, Borneo $45ka$
• Tianyuan, China $40 ka$
• Oase, Romania, $40 ka$
• The question of modern humans in China and Indonesia is ongoing.
• Several sites claim to place modern humans there by $100ka$
• All of these have been seriously questioned either due to provenience issues or dating issues

Various Scientists and Fossil Sites

• Images and locations of different scientists, fossil sites, and key fossils, including Fred Smith, Milford Wolpoff, Border Cave, Klasies River Mouth, Omo, Jebel Qafzeh, Skhul, Herto, Al Wusta, and Misliva.

Misliya Cave, Israel

• Discovered 2002, dates published 2018
• Partial maxilla and Levallois tools
• Dates from tools, enamel of tooth and crust adhering to teeth
• $174 – 185 ka$
• Some question about dates from enamel

Al Wusta, Saudi Arabia

• 2016, $86ka$

Al Wusta Details

• Discovered in 2016 by Saudia geological survey
• Stone tools (Levallois technique)
• Fauna including hippo
• $95-85 ka$ U-series of bone, OSL of tools and soil

Lunadong (Luna Cave), China

• Guangxi, China; Excavations 2004 and 2008
• Faunal remains, two hominin teeth, stone artefacts
• Biostratigraphy indicates Upper Pleistocene
• Th/U and Th/Th on flowstones
• $127-70ka$

Tooth Size Variation - Hominins

• Graph shows mesial-distal and bucco-lingual dimensions
• Older hominins have larger teeth
• Authors argue this is human, but overlaps significantly with range for neandertals as well…

Tooth Measurement

• Diagrams illustrating the mesial, distal, buccal, and lingual aspects of anterior and posterior teeth for measurement purposes.

Various Fossil Sites and Scientists

• Images and locations of different fossil sites and scientists, including Niah Cave, Madjedbebe, Zhoukoudian/Tianyuan, Lake Mungo, Kow Swamp, Russell L. Ciochon

Map of Fossil and Artifact Sites in Asia and Australia

• Map indicating fossil and artifact sites in Asia and Australia, including Luna Cave, Tam Pa Ling, Niah Cave, Liang Bua, Madjedbebe, and Lake Mungo

Sahul

• Images of Madjebebe Rock Shelter and Lake Mungo
  • Madjebebe Rock Shelter $65ka…?$
  • Lake Mungo $60-40 ka$

Ust-Ishim, Western Siberia

• Modern human, male Left Femur
• $45 ka$ – 14C direct dating
• aDNA intact – oldest modern human genome
• Neandertal gene flow as recent as 7 – 13 ka (no Denisovan)

Oldest Humans in Europe

• Peştera cu Oase and Peştera Muierii in Romania (~$36 ka$)

Various Sites and Dates

• Map showing various sites and their approximate dates, including Jebel Irhoud, Ndutu, Omo Kibish, Bodo, Herto, Ngaloba, Kabwe/Broken Hill, Florisbad, and Rising Star.

Out-of-Africa Model Predictions (Revisited)

1. AMH fossils oldest in Africa; should appear later elsewhere
2. Transitional forms only in Africa
3. Coexistence of archaic & modern humans outside Africa
4. Africa should show greatest genetic diversity b/c humans have been there longest
5. Modern human behavior should originate in Africa

Transitional Forms in Africa

• Archaic sapiens Grade
  • Grades – reflecting the different stages of evolutionary transition (rather than species designation)
  • Many of these have been classified as H. heidelbergensis or merely ‘transitional’

African Transitional Forms

• Florisbad, >$200 kya$
• Herto, $160 kya$ Homo sapiens idaltu
• Ngaloba, $130 kya$ Ngaloba, Tanzania

Out-of-Africa Model Predictions (Again)

1. AMH fossils oldest in Africa; should appear later elsewhere
2. Transitional forms only in Africa
3. Coexistence of archaic & modern humans outside Africa
4. Africa should show greatest genetic diversity b/c humans have been there longest
5. Modern human behavior should originate in Africa

Map of The Levant

• Map showing fossil sites in The Levant (~$100 kya$), including Tabun, Amud, Skhul, and Qafzeh; Neanderthal presence: Tabun, Amud (100-60 ka); Skhul V, early AMHS (120-80 ka); Qafzeh

Mitochondrial DNA

• Graph of mitochondrial DNA sequence divergence, showing Africa having the highest diversity and suggesting a last common female ancestor (