Impact of Tool Use and Technology on the Evolution of the Human Mind

Advances in DNA genotyping and sequencing technology have led to an upsurge in studies of “polygenic” influences on many human behavioral traits. In this talk, I will discuss how human cultural norms and preferences have affected, and continue to affect, patterns of genomic variation in different populations. Examples include studies of ancient and modern populations, with genetic variation obtained from the Y-chromosome and the other 22 pairs of human chromosomes.

The simple fact of tool-making no longer provides a sharp dividing line between “Man the Tool-Maker” and the rest of the animal world. It is now clear that many other species make and use tools, and that distinctly human technology emerged through a long and meandering evolutionary process rather than the crossing of some critical threshold. However, it would be a mistake to underestimate the transformative effects of tools on everything from our hands and brains to our reproductive strategies and social organization. Humans may not be uniquely defined as “a tool-using animal” but we do inhabit a uniquely elaborated technological niche. The earliest known stone tools predate evidence of brain expansion by many hundreds of thousands of years during which their occurrence was extremely patchy and discontinuous. Far from a breakthrough, stone tool-making appears to have been a fragile behavior of marginal value. This is expected for a technology located near the limits of contemporary hominin capacities, with high learning costs, limited flexibility, and high rates of failure offsetting it benefits. Natural selection acting on hominin brains and bodies during this lengthy period of experimentation may eventually have eased these costs, leading to a dramatic proliferation of “Oldowan” tool-sites after about 2.0 million years ago (mya). This is closely co-incident with the first appearance of larger-brained and –bodied Homo erectus by ~1.9 mya and was rapidly followed by the invention of more sophisticated Acheulean “handaxe” technology by 1.76 mya, marking an important inflection point in the biocultural feedback processes that eventually produced the modern human technological niche.

European paleoanthropologists developed the behavioral modernity metaphor in the 1970s, when it became clear that the archaeological record for human origins in Europe 45,000 years ago differed from that found with older “archaic” humans in Africa and Asia. Since then, archaeologists have defined behavioral modernity strategically, varying diagnostic criteria to draw attention to one or another kind of evidence. Many have cited the use of projectile weaponry as evidence for modern human behavior and cognition, but changes in projectile weaponry do not correlate with any major inflection point in human evolution. This should surprise no one, because the projectile technology-behavioral modernity link rests on little or no prior theory. Archaeologists developed it after-the-fact to explain early evidence for projectile technology. Rather than focusing on behavioral modernity, paleoanthropologists should focus on behavioral complexity. Complexity is a metaphor, too, but it is also a statistically-measurable property of any quantitative evidence. The stone tool record begins to exhibit increasingly complex variability after 0.2-0.3 million years ago, during a period correlated with Homo sapiens origin and dispersal. This complex variability most likely reflects an evolving relationship between technology and spoken language –an uniquely derived human behavior, that intensified as humans became Earth’s only obligatory tool-using primate.

Mathematics is one of the most sophisticated, precise, and abstract conceptual edifices humankind has ever created, supporting science, technology, economics, and deep philosophical investigations. Yet, mathematics is a remarkably recent invention in the history of Homo sapiens. What made it possible? One fundamental building block is “number,” whose simplest forms, conventional wisdom holds, are said to be biologically endowed and shared by many species. What is shared, however, are general mechanisms for perception of quantities, not number. Number —i.e., exact symbolic quantification, as in our familiar “seven” or “8”— is complex and abstract, and although ubiquitous in the industrialized world, is far from being present in all human cultures. While there are biologically evolved preconditions for quantity discrimination shared by many species, the presence of number (and arithmetic) proper is a cultural, not a biological trait. Exact quantification was brought to being via relatively recent (only thousands of years) cultural preoccupations and practices that were crucially supported by language-mediated cognitive tools (e.g., symbolic reference, analogical/metaphorical reasoning) and material technology (e.g., writing, abacus)— essential dimensions that lie largely outside natural selection. Language thus is a necessary—but not a sufficient— condition for number. I’ll briefly review some relevant empirical data and illustrate the power of cognitive tools with the passage from “number” to the “number line.” This 17th century move (which required conceiving numbers metaphorically as locations in space) quickly led to analytic geometry, infinitesimal calculus, differential equations, and more. The path from quantity perception—shared by many species— to number, to mathematics is a story of human “biological enculturation.”

Long before the origins of agriculture or the rise of the first cities, our species spread out across the globe into an immense diversity of environments, from the frozen tundra of Siberia to the arid deserts of Australia. Our species’ immense ecological success in these environments depended not on our vaulted intelligence or rationality, or on any array of local genetic adaptations as in other species. Instead, human survival and success depends on the inheritance of large bodies of culturally-transmitted information that accumulates and aggregates over generations to produce cultural adaptations. Our species’ degree of reliance on cultural learning means that a population’s ability to generate and maintain complex cultural repertoires, tools and technologies, such as those commonly found among hunter-gatherers, depends on its sociality, and specifically on its social norms and institutions. Thus, our apparent intelligence derives more from our collective brains than our individual intelligence. Overall, the emergence of this second system of inheritance sparked a culture-gene coevolutionary duet that has driven genetic change in our species for over a million years. Many aspects of our anatomy, physiology and psychology, from our big brains to our short colons, only make sense in the light of culture-gene coevolution.