Concluding remarks
Overall, the simulations confirmed the plausibility of the ‘cultural
drive’ hypothesis. Under suitable conditions, the runaway coevolution of
culture, social learning and brain capacity may start in a social
species. The necessary conditions include a minimum starting level of
social learning and a socio-ecological situation that ensures the
possibility of sporadic invention of different, beneficial (for the
individual or for the group) and cognitively demanding behaviours
(memes). The chances for the runaway brain-culture coevolution increase
when such memes belong to different categories: some are individually
beneficial (e.g., ‘Machiavellian’) while the others are group-beneficial
(e.g., ‘cooperative’). In this case, the runaway brain-culture
coevolution can start and proceed under varying levels of between-group
competition and migration.
Hominins, and especially the Early Pleistocene species of the genusHomo , probably found themselves in the right situation due to
changes in their social and ecological niche. The changes of the social
niche were related to the lower within-group aggression and competition,
higher paternal investment in offspring and the proposed trend towards
monogamy and social conformity. This probably resulted in new optimal
strategies for reaching higher social status and reproductive success
(individuals had to rely more on ‘Machiavellian intelligence’ than on
physical strength and violence) (Lovejoy, 2009; Stanyon, Bigoni, 2014;
Raghanti et al., 2018). The changes of the ecological niche were related
to new feeding strategies such as confrontational scavenging and
collective hunting (Bunn, Ezzo, 1993), which required high levels of
within-group cooperation (Bickerton, Szathmáry, 2011; Gavrilets, 2015)
and cognitively demanding behaviours such as the Oldowan stone tool
making (Morgan et al., 2015).
The simulation results make it possible to suggest a tentative
explanation for a somewhat counterintuitive pattern observed in
anthropogenesis: in the Early Paleolithic, while cultural development
was very slow (e.g., Beyene et al., 2013), the brain volume was
increasing rapidly; in the Middle to Late Paleolithic cultural
development accelerated greatly, while the brain ceased to increase and
even somewhat decreased from the Late Paleolithic to recent (Holloway,
2015). In our simulations, brain expansion was efficiently stimulated by
a ‘rough’, primitive culture consisting of a few large (difficult to
learn) memes. Later, as the culture becomes more ‘sophisticated’ (that
is, saturated with numerous small but efficient memes), the brain
expansion slows down and even reverses. The mechanism underlying this
pattern, which we dubbed ‘the vicious circle of meme simplification’,
requires the combination of two types of limitations: for brain
expansion and for the amount of knowledge that can be learned in a
lifetime. Another requirement is that the available mechanisms of social
learning must give a strong selective advantage to smaller memes. Under
such conditions, increasing costs of brain expansion result in stronger
selection for smaller memes, which, in turn, makes larger brains less
beneficial.
However, brain expansion can receive additional boost if such means of
social learning evolve that are at the same time (1) costly in terms of
brain expansion (rely on many complicated neuronal curcuits) and (2) are
tolerant to meme complexity, that is, make it possible to learn and
teach difficult skills and concepts relatively easily. Such mechanisms
of social learning can break or weaken ‘the vicious circle’, so that the
brain expansion will be able to proceed further. Human language is
probably just such a kind of a social learning mechanism. We tentatively
suggest that the extraordinarily fast brain expansion in the course of
human evolution, which later opened unique possibilitities for the
development of civilization, was probably a kind of evolutionary
accident: the cultural drive was just too strong for the brain to evolve
in a more balanced way, e.g., by structural optimization rather than by
disproportionate increase in volume and the number of cortical neurons.
The results also suggest that the runaway brain-culture coevolution can
acquire additional acceleration from two positive feedback loops: via
population growth and via lifespan extension (e.g., if cultural
development results in lower mortality rate) (fig. 10).
The results also imply that between-group competition (1) tends to make
culture less diverse, (2) facilitates the propagation of
group-beneficial memes, (3) effectively removes parasitic memes from the
meme pool. Cultural group selection (that is, selective survival and
propagation of groups with more efficient cultures) shapes the content
of the meme pool, while individual selection is almost unable to do so.
Due to the horizontal spread of memes, culture is a group characteristic
rather than an individual one.