De Vries shows the probability that species go on for long periods
showing only fluctuations, and then suddenly take to sporting in the
way described, short periods of mutation alternating with long
intervals of relative constancy. It is to mutations that De Vries
and his school, as well as Luther Burbank, the great former of new
fruit- and flower-plants, look for those variations which form the
material of Natural Selection. In "God the Known and God the
Unknown," which appeared in the Examiner (May, June, and July), 1879,
but though then revised was only published posthumously in 1909,
Butler anticipates this distinction:-


"Under these circumstances organism must act in one or other of these
two ways: it must either change slowly and continuously with the
surroundings, paying cash for everything, meeting the smallest change
with a corresponding modification, so far as is found convenient, or
it must put off change as long as possible, and then make larger and
more sweeping changes.

"Both these courses are the same in principle, the difference being
one of scale, and the one being a miniature of the other, as a ripple
is an Atlantic wave in little; both have their advantages and
disadvantages, so that most organisms will take the one course for
one set of things and the other for another. They will deal promptly
with things which they can get at easily, and which lie more upon the
surface; THOSE, HOWEVER, WHICH ARE MORE TROUBLESOME TO REACH, AND LIE
DEEPER, WILL BE HANDLED UPON MORE CATACLYSMIC PRINCIPLES, BEING
ALLOWED LONGER PERIODS OF REPOSE FOLLOWED BY SHORT PERIODS OF GREATER
ACTIVITY . . . it may be questioned whether what is called a sport is