for humans.
Henrich notes that cultural evolution initially faced a start-up problem: it had to provide both a bigger brain and more meanings. A small brain cannot retain too many meanings, and a bigger brain is not needed if there is nothing to learn. So, how could we jump-start the cumulative engine of cultural evolution? To make a leap over a chasm that can only be crossed in two leaps, you need a “bridge.”
“Once cumulative cultural evolution is up and running, it can create a rich cultural world, full of adaptive tools, techniques, and know-how that can more than pay the costs of building and programming up a larger brain designed and equipped for cultural learning. However, in the beginning, there won’t be much out there to culturally acquire, and what is there will be simple enough that it will still be learnable by one’s own individual learning efforts (without social learning), by trial and error for example. Thus, natural selection may not favor larger brain size or complexity, because brains are costly to develop and program” (Henrich 2016, p. 297).
According to Henrich’s hypothesis, the “bridge” problem was solved by two intertwined pathways (Henrich 2016, pp. 298 ff.). First, by multiplying meanings without notably increasing the size of the brain: in open areas with many predators large hominid groups formed for collective defense and exchange of meanings. Second, by reducing the costs of creating and maintaining larger brains. Henrich believes that female hominids, in order to avoid inbreeding, left their group upon reaching sexual maturity and moved to the neighbors, losing all family ties. The formation of stable protofamilial pairs in large groups, in which the child’s kinship could be established not only through the maternal, but also through the paternal side, made it possible to form a circle of relatives of the mother by marriage, that is, the child’s relatives (alloparents). This spread the burden of child-rearing among a larger number of individuals, thereby extending both the time in which the child could acquire a culture and the size of his brain.
Other hypotheses can also be put forward regarding the “missing link,” that is, the practices of self-reproduction that made it possible to build a bridge between the mental abilities of higher primates and the intelligence of Homo sapiens, living in the world of symbols. Evgeniy Panov believes that the entrance to the bridge has been discovered, but most of it has not been preserved, and the remains may never be found (Panov 2012, p. 383).