Meeting Abstract
Hardy’s Aquatic Ape Theory proposes that humans evolved to become a two-legged hairless creature via a semi-aquatic diversion that took place around the Pliocene, and that access to marine-based food was a major selective force for this diversion. Among aquatic vertebrates, the most common prey capture strategy is suction feeding. By rapidly expanding the mouth cavity, suction feeders generate a fluid flow outside of their mouth, drawing prey inside. Suction feeding has repeatedly and secondarily evolved in aquatic vertebrates, including marine mammals. However, it is unclear whether humans possess this ability, as could be expected based on their proposed (albeit controversial) history. Using a high-speed flow visualization technique, we characterized the spatio-temporal patterns in the flow fields produced during suction feeding in Homo sapiens. We found that mouth opening speed was an order of magnitude slower in Homo sapiens compared to fishes. The speed of suction flows was 5x slower than expected based on H. sapiens gape diameter (ca 5 cm), and equivalent to that of fish with a gape of about 1cm. Further, flows were not unidirectional; high efflux out of the mouth was observed during mouth closure. Taken together, our results indicate that H. sapiens are poor underwater feeders. Adaptations for suction feeding either never existed or have regressed since the Pliocene. Our study therefore failed to provide support for the Aquatic Ape Theory.
