  We optimize three-dimensional snake kinematics for locomotor efficiency. We
assume a general space-curve representation of the snake backbone with
small-to-moderate lifting off the ground and negligible body inertia. The cost
of locomotion includes work against friction and internal viscous dissipation.
When restricted to planar kinematics, our population-based optimization method
finds the same types of optima as a previous Newton-based method. A few types
of optimal motions prevail. We find an s-shaped body with alternating lifting
of the middle and ends for small-to-moderate transverse friction. For large
transverse friction, curling and sliding motions are typical with small viscous
dissipation, replaced by large-amplitude bending with large viscous
dissipation. With small viscous dissipation we find local optima that resemble
sidewinding motions across friction coefficient space. They are always
suboptimal to alternating lifting motions, with average input power 10--100\%
higher.
