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Chapter 22 — Gradualism Can Do It All
Gradualism is the backbone of evolutionary thinking. Darwin wrote in On the
Origin of Species that natural selection advances only
“by short and sure,
though slow steps.
” Applied to human evolution, this means that cognition, like
anatomy, emerged gradually — through tiny improvements over vast stretches
of time. In this view, there was no Adamic threshold, no sudden ignition, only a
slope of continuous change.
Why Gradualism Persuades
It fits fossil continuity.
At Jebel Irhoud (~315,000 years ago), fossils already show modern-looking
faces, though with elongated skulls (Hublin et al., 2017).
At Omo Kibish I in Ethiopia (~195,000 years ago), the skeleton is fully
modern in form.
At Herto (~160,000 years ago), brain volume falls within today
’s range
(McDougall et al., 2005).
Taken together, these suggest a slow slope toward modern anatomy.
It matches tool evolution.
Acheulean handaxes (~1.7 million years ago) gave way to Middle Stone Age
flake tools (~300kya).
Later, Upper Paleolithic blades (~50kya) appear, more refined but still part
of a long arc.
Tool development looks incremental.
It resonates with common sense.
Languages evolve word by word, technologies improve generation by
generation, children grow step by step. Why should cognition be any
different?
Gradualism feels natural, elegant, and faithful to Darwin’s slope.