How did gastropods evolve torsion? I have looked all over. There doesn’t seem to be any clear idea of what torsion does now, let alone what purpose it served long ago. There was a hypothesis (Garstang’s hypothesis) that the veligar larvae developed torsion so they could pull their little heads into their little shells. However, that appears to have been disproved in 1985. This link tells why. http://www.mbari.org/staff/peti/Pubs/Gastropod Torsion-A Test of Garstang's Hypothesis.pdf “in only one case was rate of predation reduced in pretorted larvae. It therefore appears that torsion does not function defensively,…” The inheritance of torsion involves a weird delay in phenotypic expression. The gene expresses itself in the offspring of the mother. Aside from the interesting questions in development it brings up, this suggests some very twisted natural selection. http://science.naturalis.nl/media/280795/schilthuizendavisonnawi.pdf “In the few species that have been characterized, chirality is determined by a single genetic locus with delayed inheritance, which means that the genotype is expressed in the mother’s offspring…Nevertheless, chiral reversal could still be a contributing factor to speciation (or to divergence after speciation) when reproductive character displacement is involved.” Here it is 2009, and students are still writing theses on what they don’t know about torsion. Apparently the torsion makes some snails more sensitive to ocean acidification. However, there is no evidence that it makes the snail less sensitive to anything else. So why evolve it? http://www.escholarship.org/uc/item/39q8w7gh It almost appears that mainstream science has given up on explaining the evolution of torsion in gastropods. Anyone have any other ideas?