Practice question

Bilateral symmetry associated intimately with cephalization and directed active locomotion because anteroposterior axis established by Wnt β-catenin and Hox patterning drives concentration of sensory receptors, cerebral ganglia and mouth anteriorly encountering environment first. Forward crawling or swimming predators benefit from anterior processing reducing reaction time, selective advantage during Cambrian evolutionary arms race. Sessile radial animals maintain circumferential nerve nets without brain, radial cleavage refers to early embryonic pattern not adult symmetry, diploblastic condition independent of symmetry, thus cephalization best correlates bilaterality.