THE PLANTAR REFLEX - RePub

curious case of one healthy infant (probably his own) in whom the
Babinski signs disappeared at the age of about six months- apparently not
related to walking, but with a time lag between right and left similar to
that in the previous 'discovery' of the hands. Conversely, a normal plantar
response in rachitic children who were yet unable to support themselves
on their legs was observed by Passini (1900) and Engstler (1905).
Sehestedt ( 1933) examined sixty-two older children who had been bedridden
for months or years from 'surgical tuberculosis' and found a
Babinski sign in ten. These children may not have been free from
involvement of the brain or spinal cord, and persistent upgoing toe signs
and delayed walking can of course both result from brain damage. There
seem to be no distinguishing features between the physiological and
pathological infantile response (Holt, 1961).
We can conclude that, although there is probably some physiological
connection between the onset of walking and the appearance of the adult
plantar response, as both changes depend on the functional development
of descending pathways, a direct relationship has not been borne out by
observations in individual children.
Science or fiction?
TELEOLOGICAL SPECULATIONS
Whether teleological considerations have a place in scientific thinking
depends upon the definition of science one adheres to. Many contemporary
biologists regard any discussion of 'design' as adverse to the objectivity of
Nature and therefore as outside the realm of science (Monod, 1970). On
the other hand it is a basic principle that, in general, all beings (it is
difficult to avoid the word 'creature' here) strive towards survival and
reproduction. It is clear that many biological features are 'useful' here.
When one thus reverses cause and effect and substitutes 'use' for 'purpose',
it becomes much more acceptable to ascribe a function to any particular
biological structure or phenomenon - provided the survival value is
evident (Lorenz, 1963). All other explanations are unfalsifiable, and, in
consequence, incompatible with an operational definition of science. Now
it is self-explanatory that animals or humans without legs, eyes or pain are
at risk in the process of natural selection, but it is difficult to see how
absence of the plantar toe reflex (or of the knee jerk, for that matter)
interferes with fulfilment of primary biological aims.
During the first half of this century, guesswork about the purpose of
reflexes was more respectable than it is today, although it was often veiled
under terms like 'physiological significance'. The following survey is given
mainly for historical reasons.
47