Mysterious hominin species

Question 1

Denisovans and mtDNA/nDNA

Answer 1

mtDNA - Krause et al. 2010
nDNA - Reich et al. 2010

Denisovans described as a new species

Based on the analysis of mtDNA, inferred to be a sister group to both Neanderthals and modern humans.

Based on nDNA, Denisovans are a sister group to Neanderthals (to the exclusion of modern humans)

No formal species definition, just informally referred to as Denisovans

First species to be described (but not formally defined) based on genetic differences with others

No anatomical description or holotype

Question 2

Denisovans

Answer 2

We know a lot about genetics of Denisovans but almost nothing about their anatomy.

Some Asian fossils - usually classified as H. erectus & H. heidelbergensis - may be Denisovans

Need to find Denisovan aDNA in fossils OR find more fossil evidence from Denisova

4-6% of Denisovan DNA in present-day Melanesians. Adaption to high altitude mediated by a Denisovan gene.

Question 3

Adaptions to high altitude

Answer 3

Adaption to high altitude mediated by a Denisovan gene.

Over 4000m, air has 60% less oxygen than at sea level

Common to all populations: ability to maintain relatively low levels of haemoglobin

TIBETANS:
Elevated lung capacity - large amounts of air per unit of time compensate for low oxygen levels
Haemoglobin level not significantly different from people living at low altitude - no chronic mountain sickness
Adaption to high altitude in Tibetan populations mediated by the Denisovan variant of the gene EPAS1

Question 4

EPAS1

Answer 4

Adaption to high altitude in Tibetan populations mediated by the Denisovan variant of the gene EPAS1

Denisovan haplotype present in 80% of Tibetans and about 1% of Han Chinese

Change happened less than 3000 years ago, when the Tibetans split from Han Chinese

Fastest genetic change observed in any human gene

Modern humans acquired the Denisovan variant of EPAS1 through an early hybridisation (50kya)

Later selected in high-altitude Tibetans during the last 3000 years.

EPAS1 variant correlates with decreased haemoglobin concentrations among Tibetans

Hallmark of their adaption to hypoxia

Question 5

Homo floresiensis - holotype, site, dating

Answer 5

Discovery in 2003, Liang Bua Cave, Flores, Indonesia

Holotype - LB1 skeleton

Initially dated to 18kya but new analyses indicate 60-100kya - extinction related to arrival of H. sapiens?

Question 6

H. floresiensis adaptions

Answer 6

1. Very small brain and body size for a late hominin - reduction in size from larger hominins
2. Very young geological age - overlapped with modern humans
3. No land connection between Flores island and mainland Asia even when sea levels were lowest - required sailing or rafting. Could have resulted from a tsunami or tsunami-like event (van den Bergh et al, 2009)

Question 7

H. floresiensis cranial anatomy

Answer 7

Very small brain size - 426cc

Reduced prognathism, depressed infraorbital region

Low cranial vault

Slight sagittal keel

Small posterior teeth with M3 reduction

No chin

Strong asymmetry

Question 8

H. floresiensis postcranial anatomy

Answer 8

106cm, 28kg

Combination of derived and primitive traits in upper limb

Primitive wrist anatomy - less manual dexterity

Robust long bones

Primitive, relatively large feet - less efficient bipedal locomotion?

Dwarf species evolved from H. erectus or evolution from already small H. habilis or Australopithecus?

Question 9

H. floresiensis - new species or pathological individual?

Answer 9

Strong facial asymmetry

Developmental anomalies e.g. rotated premolars

Growth hormone insensitivity (Laron syndrome), Down’s syndrome - different syndromes/pathologies to explain Flores traits

Hard to explain that they reproduce early hominin anatomies

Fossil hominins other than H. sapiens can have anomalies

At least nine additional individuals (Morwood et al 2005) - equally small but only one cranium. Would a rare developmental disorder affect so many individuals?

Question 10

The island rule

Answer 10

H. floresiensis found in association with island fauna: dwarf elephant, giant rats, Komodo dragon

Island rule

• Large animals tend to decrease in size - less resources are needed, no competition
• Small animals tend to increase in size - absence of predators

Question 11

H. floresiensis - archaeology

Answer 11

Similar flake stone tools to Oldowan technology

Evidence of butchery and hunting

Evidence of fire

Question 12

Evolution of H. floresiensis

Answer 12

Insular dwarfism from H. erectus - supported by cranial traits

Body mass reduced to 55%
Brain size reduced to 50%
In other dwarf mammals, brain size shrinks substantially less than body size

Evolution from H. habilis - supported by postcranial traits
Body mass reduced to 85%
Brain size reduced to 70%
Putative relationship with H. habilis would not imply such a strong reduction in absolute size but relative reduction in brain size would surpass relative reduction in body size
Important implications for hominin migrations

Question 13

Tools from Flores

Answer 13

Wolo Sege, Flores - 1mya - who made them?

Simple tools similar to ones found in association with H. floresiensis in Liang Bua - technological continuity with H. floresiensis tools?

Question 14

New fossils from Flores (2016)

Answer 14

Mata Menge, 700kya

van den Bergh et al 2016

Mandibular fragment and some teeth

Belong to one adult and two children

H. floresiensis-like - persistence of hominin lineage in Flores island - limited space and resources - over a 1m year period

• Energetic models - more small-bodied hominins could persist on Flores than larger-bodied hominins
• Inbreeding may impact variability
• Frequent tsunamis and volcanic eruptions in the region would have affected all taxa
• At least one turnover event recorded at 900kya

Very rapid dwarfing - 300k years - from H. erectus size to H. floresiensis size (if Wolo Sege tools were H. erectus) - 50% reduction

• Red deer on Jersey - 56% of mainland size in 6-10 years
• Dwarf mammoths on California channel islands - 10% of mainland size in 85k years

Where is the evidence indicating a pre-erectus migration out of Africa?

Question 15

H. floresiensis - implications for early human migrations

Answer 15

If H. floresiensis evolved from H. habilis or Australopithecus, these hominins must have left Africa before H. erectus did - pre-OOA I migration?

No reason to think that H. habilis/Australopithecus couldn’t migrate out of Africa, but no evidence so far

• Dmanisi, 1.8mya - more primitive than classic H. erectus
• Shangchen, 2.1mya - stone tools made by unknown hominin

Question 16

Dinaledi chamber

Answer 16

Rising Star cave system, South Africa

Large assemblage of fossil hominins

More than 1500 fossils, 15 individuals

Definition of the new species H. naledi

Question 17

Lesedi chamber

Answer 17

Rising Star cave system, South Africa

More than 100 fossils, at least 3 individuals

Every anatomical region represented apart from tibia, fibula, and foot bones

Question 18

H. naledi - cranial anatomy

Answer 18

Homo traits:
Small molars
Gracile mandible
Parabolic dental arcade

Homo ergaster-like traits:
Shape of the brain case
Occipital bone morphology

But very small brain - lowest value within genus excluding H. floresiensis - 465-610cc
Less pronounced browridge than H. erectus
Postorbital constriction

Question 19

LES1

Answer 19

‘Neo’

H. naledi from Lesedi chamber

Fragmented cranium, though cranial vault, facial regions, and manidble preserved

Cranial capacity 610cc

Similarities to Dinaledi chamber specimens

Less pronounced browridge than H. erectus

Rounded braincase

Subnasal prognathism

Small size

Question 20

H. naledi brain

Answer 20

Organisation of the inferior frontal region similar to later Homo, in spite of small brain size

Some aspects of brain reorganisation predating increase in brain size

Question 21

H. naledi

Answer 21

Rising Star cave system, South Africa

Support for H. naledi falling within Homo clade

Sister taxon to H. antecessor and later Homo.

Dirks et al. (2017) - 236-335kya

• Uranium-thorium disequilibrium
• Electron spin resonance
• Radiocarbon
• Optically stimulated luminescence (OSL) dating

150cm
EQ below all Homo species except Dmanisi fossils and H. floresiensis

Question 22

H. naledi hand morphology

Answer 22

Human-like hand, exceptionally complete

No H. ergaster hands for comparison

Mosaic morphology

• Curved phalanges
• Unique first metacarpal morphology

Good precision grip but no association with stone tools

Question 23

H. naledi femur and foot

Answer 23

Long femoral neck
Modern human-like foot - transverse arch and adducted hallux

Indicates adaptions towards bipedalism

Question 24

H. naledi - origin of the accumulation

Answer 24

Bone taphonomy indicates that hominin individuals reached the chamber complete, with disarticulation occuring during or after deposition - deliberate body disposal in a single location (VERY controversial)

Other possible explanations:
Bones transported from a different location in the cave system
Catastrophic event (e.g. a flood)
Death trap
Carnivore activity
'Housekeeping'

Question 25

What do mysterious hominin species show?

Answer 25

1. Much more diversity during hominin evolution than previously thought = more to be found?
2. Even until quite recently - 200-300kya, even less than 100kya
3. Unexpected evolutionary trajectories