Where does saltation collide?

In geomorphology, saltation (from the Latin for leaping) is a mode of sediment transport in which grains too heavy to stay suspended travel by a series of short hops: wind or flowing water lifts a grain, it arcs forward, and on landing it dislodges other grains that leap in turn, so the whole bed moves in a cascade of bouncing particles. Bagnold's 1936 The movement of desert sand measured these trajectories and showed that saltation drives the formation and advance of dunes. The referent is a particle-transport mechanism defined by the hopping path and the impact-driven chain reaction, quantified by grain path length and transport rate, a wholly different thing from a sudden evolutionary jump that shares the word.[1]

Unit

The sediment transport rate carried by hopping grains, and their hop length

Recovery means

Not applicable

Measured by

Measured by sediment traps, high-speed imaging of grain trajectories, and the threshold wind or shear stress for grain movement

In evolutionary biology, saltation is the idea that a new form can arise in a single large step rather than through the slow accumulation of small changes, so that one or a few mutations with big developmental effects produce a markedly different, potentially viable organism in one generation. Theißen's 2009 Saltational evolution: hopeful monsters are here to stay reviews the modern evidence, through developmental and homeotic mutations, that such large-effect jumps occasionally matter. The referent is a mode and tempo of evolutionary change, a discontinuous leap in form across generations, measured against the gradualist baseline, and it has nothing to do with a sand grain's hop beyond the shared image of leaping.[2]

Unit

The size of a phenotypic jump produced in a single evolutionary step

Recovery means

Not applicable

Measured by

Evidenced by large-effect (e.g. homeotic) mutations, discontinuities in the fossil or morphological record, and the viability of macromutant forms