Two chapters, the same questions asked of both
Put two Deep Time chapters next to each other — their evidence base, the dating methods behind them, the live debates, and the questions still open.
Australopithecus
Bipedalism before big brains — Lucy, Laetoli, and what the fossils can support.
Open full chapter →Homo Habilis
The first toolmakers, and the ongoing argument about where the genus Homo begins.
Open full chapter →Fragmentary hominin fossils, footprint trackways, and the volcanic layers that bracket them in East and southern Africa.
Cranial and dental fragments alongside early flaked stone assemblages and cut-marked animal bone.
| Method | What it constrains |
|---|---|
| Argon–argon dating of volcanic tuffsAsh layers above and below fossil horizons | Brackets a fossil between two dated eruptions. Precision depends on how close those layers are. |
| Functional morphologyPelvis, femur, foot and vertebral remains | Establishes locomotor capability. It does not tell us how much time was spent in trees. |
| Ichnology (trackway analysis)Preserved footprints in dated ash | Records gait directly. Attribution to a specific species is inferred from context. |
| Method | What it constrains |
|---|---|
| Lithic analysis and refittingOldowan cores, flakes and debitage | Demonstrates intentional knapping and sometimes reconstructs the sequence of blows. It does not identify the knapper's species. |
| TaphonomyCut marks, percussion marks and carnivore tooth marks on bone | Distinguishes hominin from carnivore modification. Order of access is argued case by case. |
| Endocast measurementCranial interiors | Gives volume. It says little on its own about cognitive organisation. |
How arboreal were these species?
Upper-limb anatomy retains climbing features while lower-limb anatomy is committed to walking.
Which australopith lineage, if any, leads to Homo?
Candidates exist; the fossil sample is too sparse to settle descent.
Is Homo habilis a coherent species or a wastebasket taxon?
The referred specimens show variation some researchers read as multiple species.
Hunting or confrontational scavenging?
Both leave overlapping bone-surface signatures.
- What selected for bipedalism in the first place?
- How many contemporary hominin species were there?
- How much of the record is missing outside the East African rift, where preservation favours discovery?
- Who made the earliest flaked tools?
- Was meat a driver of encephalisation or a consequence of other changes?
- How should the early Homo specimens be sorted taxonomically?