Evolution of brain ontogenetic growth under ecological challenges

9 Large brains are metabolically expensive but support skills (or cognitive abilities, knowledge, 10 information, etc.) that allow overcoming ecological and social challenges, with social challenges 11 being thought to strongly promote large-brain evolution by causing evolutionary arms races in 12 cognition yielding exaggerated brain sizes. We formulate a mathematical model that yields quan13 titative predictions of brain and body mass throughout ontogeny when individuals evolve facing 14 ecological but no social challenges. We find that ecological challenges alone can generate adult 15 brain and body mass of ancient human scale, showing that evolutionary arms races in cognition 16 are not necessary for extreme brain sizes. We show that large brains are favored by intermediately 17 challenging ecological environments where skills are moderately effective and metabolically ex18 pensive for the brain to maintain. We further show that observed correlations of cognitive abili19 ties and brain mass can result from saturation with skill maintenance of the brain metabolic rate 20 allocated to skills. 21 1 . CC-BY-NC 4.0 International license not peer-reviewed) is the author/funder. It is made available under a The copyright holder for this preprint (which was . http://dx.doi.org/10.1101/050534 doi: bioRxiv preprint first posted online Apr. 27, 2016;