They propose that human fat deposits are crucial buffers that ensure provision of fuel to feed the hungry brain, and their findings support the notion that a concomitant increase in brain size and fat storage could only be facilitated in an environment, such as shallow-water aquatic ecosystems, providing a stable and abundant supply of resources rich in energy and LC-PUFA (such as EPA and DHA) that constitute limiting factors for neurodevelopment and functioning. In fact, LC-PUFA might also have played an important role in the development of human adipose tissue. For example, while the brain contains the highest concentrations of DHA, it contains only 23% of total DHA stored in the human body. The human adipose tissue in contrast, consisting mainly of saturated and monounsaturated fatty acids for energy generation, contains 50% of the total DHA stored in the human body (Kuipers et al., 2012b, c). This DHA storage is most critical in infants when the brain is developing. Cunnane et al. (2000) have shown that adipose tissue stores at birth have enough DHA to meet the growing brain's DHA requirement for about three months.
As in selection for increasing brain size, sexual selection may also have been relevant when considering the development of fat deposits (buttocks, thighs, breasts) on the human body, influencing the waist-hip ratio and hence the attractiveness to mates (e.g., Lassek and Gaulin, 2008). Sexual selection of intelligence is not contradictory to sexual selection of fat but, instead, mutually enforcing: the typically preferred low waist-hip ratio indicates presence of critical resources for brain development. Hence, the review of Lassek and Gaulin (2008) suggests that there is a functional link between two highly derived human traits, namely a very large brain and sexually dimorphic fat distributions.
We concede that at present, finding the definite explanation for the explosive hominin brain increase remains a matter of more research, and many factors may be involved (e.g., the cooking of food; Wrangham and Carmody, 2010). We conclude that exploita-
tion of aquatic food resources could have facilitated initial moderate hominin brain increase as first observed in fossils dated to c.2 Ma, and could have nutritionally contributed to the extreme brain increase (and fat storage) later on. However, it appears to be un-
likely that aquatic resource exploitation was the sole driver for the extreme brain growth and development in the later members of the human lineage.