Cicero says that the famous physician Hippocrates has left in writing
that he had suspected that a certain pair of brothers were twins,
from the fact that they both took ill at once, and their disease
advanced to its crisis and subsided in the same time in each of
them.[185] Posidonius the Stoic, who was much given to astrology,
used to explain the fact by supposing that they had been born
and conceived under the same constellation. In this question the
conjecture of the physician is by far more worthy to be accepted,
and approaches much nearer to credibility, since, according as the
parents were affected in body at the time of copulation, so might the
first elements of the fœtuses have been affected, so that all that
was necessary for their growth and development up till birth having
been supplied from the body of the same mother, they might be born
with like constitutions. Thereafter, nourished in the same house, on
the same kinds of food, where they would have also the same kinds of
air, the same locality, the same quality of water,--which, according
to the testimony of medical science, have a very great influence,
good or bad, on the condition of bodily health,--and where they
would also be accustomed to the same kinds of exercise, they would
have bodily constitutions so similar that they would be similarly
affected with sickness at the same time and by the same causes. But,
to wish to adduce that particular position of the stars which existed
at the time when they were born or conceived as the cause of their
being simultaneously affected with sickness, manifests the greatest
arrogance, when so many beings of most diverse kinds, in the most
diverse conditions, and subject to the most diverse events, may have
been conceived and born at the same time, and in the same district,
lying under the same sky. But we know that twins do not only act
differently, and travel to very different places, but that they
also suffer from different kinds of sickness; for which Hippocrates
would give what is in my opinion the simplest reason, namely, that,
through diversity of food and exercise, which arises not from the
constitution of the body, but from the inclination of the mind, they
may have come to be different from each other in respect of health.
Moreover, Posidonius, or any other asserter of the fatal influence of
the stars, will have enough to do to find anything to say to this,
if he be unwilling to impose upon the minds of the uninstructed in
things of which they are ignorant. But, as to what they attempt to
make out from that very small interval of time elapsing between
the births of twins, on account of that point in the heavens where
the mark of the natal hour is placed, and which they call the
"horoscope," it is either disproportionately small to the diversity
which is found in the dispositions, actions, habits, and fortunes
of twins, or it is disproportionately great when compared with the
estate of twins, whether low or high, which is the same for both of
them, the cause for whose greatest difference they place, in every
case, in the hour on which one is born; and, for this reason, if the
one is born so immediately after the other that there is no change
in the horoscope, I demand an entire similarity in all that respects
them both, which can never be found in the case of any twins. But if
the slowness of the birth of the second give time for a change in the
horoscope, I demand different parents, which twins can never have.