Neanderthals, Energetic Return on Intelligence, and the Division-of-Labor Threshold of Technical Takeoff

Why did Neanderthals, despite substantial intelligence, technical skill, and cumulative culture,fail to generate civilization-scale technical takeoff? This article develops a formal explanatorysynthesis centered on the energetic return on intelligence. The core claim is not that intelligencewas absent, but that technical takeoff depends on whether a lineage can sustain a sufficiently largeand connected effective cultural population to preserve shared knowledge, coordinate specialists,and deepen the division of labor. Intelligence matters through a demographic and organizationalmedium.I present a reduced-form framework in which per-capita maintenance cost, usable ecologicalenergy, interaction density, and coordination burden jointly determine retained cultural complexityand the feasible depth of specialization. Extending a demographic model of cumulative culturewith a Becker-Murphy-style treatment of coordination-constrained specialization, I show howmodest per-capita energetic penalties can propagate into lower effective cultural populationsize, smaller shared knowledge pools, and reduced specialization depth. The carrying-capacityargument is clarified by distinguishing ecological carrying capacity, which determines howmany bodies a landscape can support, from derivative network capacity, which determines howmany camps, mates, teachers, exchange partners, and repair pathways remain within practicalinteraction range. A sensitivity analysis treats the Neanderthal energetic differential as uncertainrather than fixed and shows that even smaller 1–4% penalties can materially reduce retainedcultural complexity in near-threshold populations.The Neanderthal case is treated as the principal empirical application and constraint forthe theory, not as a fully calibrated historical reconstruction. Archaeological, genomic, andecological evidence is broadly compatible with a regime of somewhat higher maintenance cost,smaller and more weakly connected metapopulations, and therefore lower capacity to preserverare skills and sustain differentiated specialist roles over long horizons. Recent genomic evidenceof recurrent modern-human-to-Neanderthal gene flow, long local isolation, and analyticallyplausible downstream genetic dilution is interpreted not as a rival to demographic weakness butas a late-stage consequence that becomes more likely once populations are small, fragmented,and weakly connected. More broadly, the article argues that civilization-scale technical takeoffrequires sufficient energetic support for a deep enough division of labor, and that demographic andnetwork thinning can prevent that threshold from being crossed even in a lineage of substantialintelligence and cumulative skill.