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170 HERBERT SPENCER

modifications, we are reminded of the pot calling
the kettle black.

Spencer made his position stronger by adducing
what he calls negative evidence, namely those " cases
in which traits otherwise inexplicable are explained
if the structural effects of use and disuse are
transmitted."

(i) First he refers to the co-adaptation of co-operative parts.
With the enormous antlers of a stag there is associated a
large number of co-adaptations of different parts of the body,
and similarly with the giraffe's long neck and the kangaroo's
power of leaping. Spencer argued that the co-adaptation of
numerous parts cannot have been effected by natural selection,
but might be effected by the hereditary accumulation of the
results of use. The difficulty is to discover how much deep-
seated co-adjustment can be effected by exercise even in
the course of a long time, and the theory requires such data
before it can be more than a plausible interpretation, with
certain a priori difficulties against it. If an animal suddenly
takes to leaping many individual adjustments to the new
exercise will arise; if the animals of successive generations
leap yet more freely, they will individually acquire more
thorough adjustments up to a certain limit; meanwhile there
may arise constitutional variations making towards adaptation
to the new habit, and under the screen of the individual
modifications these may increase from minute beginnings till
they acquire selection-value. Professors Mark Baldwin,
Lloyd Morgan, and Osborn, have all made the same useful
suggestion that adaptive modifications acquired individually
may act as the fostering nurses of constitutional variations in the
same direction until these coincident variations are large enough
in amount to be themselves effective.

(2) Secondly, Spencer dwelt upon the notably unlike
powers of tactile discrimination possessed by the human skin,
and sought to show that while these could not be interpreted
on the hypothesis of natural selection or on the correlated
hypothesis of panmixia, they could be interpreted readily if the
effects of use are inherited. But the difficulty again is to



	170 HERBERT SPENCER modifications, we are reminded of the pot calling the kettle black. Spencer made his position stronger by adducing what he calls negative evidence, namely those " cases in which traits otherwise inexplicable are explained if the structural effects of use and disuse are transmitted." (i) First he refers to the co-adaptation of co-operative parts. With the enormous antlers of a stag there is associated a large number of co-adaptations of different parts of the body, and similarly with the giraffe's long neck and the kangaroo's power of leaping. Spencer argued that the co-adaptation of numerous parts cannot have been effected by natural selection, but might be effected by the hereditary accumulation of the results of use. The difficulty is to discover how much deep- seated co-adjustment can be effected by exercise even in the course of a long time, and the theory requires such data before it can be more than a plausible interpretation, with certain a priori difficulties against it. If an animal suddenly takes to leaping many individual adjustments to the new exercise will arise; if the animals of successive generations leap yet more freely, they will individually acquire more thorough adjustments up to a certain limit; meanwhile there may arise constitutional variations making towards adaptation to the new habit, and under the screen of the individual modifications these may increase from minute beginnings till they acquire selection-value. Professors Mark Baldwin, Lloyd Morgan, and Osborn, have all made the same useful suggestion that adaptive modifications acquired individually may act as the fostering nurses of constitutional variations in the same direction until these coincident variations are large enough in amount to be themselves effective. (2) Secondly, Spencer dwelt upon the notably unlike powers of tactile discrimination possessed by the human skin, and sought to show that while these could not be interpreted on the hypothesis of natural selection or on the correlated hypothesis of panmixia, they could be interpreted readily if the effects of use are inherited. But the difficulty again is to