Page 98 - Flipping book The Adam Paradox Hypothesis - Second Edition.pdf

The Ādam Paradox Hypothesis 75
The Evolutionary Threshold Model
Evolutionary anthropology generally rejects the idea of a sudden rupture.
Instead, it proposes a convergence account: symbolic thought did not emerge
all at once but accumulated gradually, and its explosion around 70kya reflects
not an ignition but the alignment of many interacting forces. In this view, the
ingredients were long in place, but only when they converged did symbolism
become visible and enduring.
Hardware Without Software
The first pillar of the convergence model stresses that having a modern-sized
brain does not guarantee symbolic thought. By ~200kya, humans possessed
cranial capacities between 1,300 and 1,500 cubic centimeters — fully within the
modern range. The fossils of Jebel Irhoud, Omo Kibish, and Herto
demonstrate this. But as Terrence Deacon argued in The Symbolic Species
(1997), symbolic thought depends less on brain size than on how the brain is
wired. Developmental timing, cortical layering, and patterns of connectivity
matter as much as raw volume. Evolutionary theorists therefore argue that
symbolic cognition required not only anatomical readiness but fine-tuned
neural “software” that developed more gradually.
Claim. By ~200–160kya, humans had modern-range anatomy, but symbolic
cognition depends on developmental timing and wiring, not size alone
(Deacon, 1997).
Case studies / anchors.
Jebel Irhoud (~315kya), Omo Kibish (~195kya), Herto (~160kya): cranial
forms and endocranial volumes within modern human range, yet no
continuous symbolic suite follows immediately.
Neanderthals: comparable brain volumes and some symbolic behaviors
(pigments, beads, burials), but traditions remain fragile. This supports the view
that anatomy ≠ stable symbolic system.
Takeaway. Large brains are necessary but insufficient; regulatory programs
(developmental “software”) must be tuned.