Thomas Hunt Morgan sums up the present situation in the following words:
"To-day the theory has few followers among trained investigators, but it
still has a popular vogue that is wide-spread and vociferous." And we
may add that the extent of its spread is directly proportioned to the
need felt for this doctrine as a support of the theory of evolution,
while the vociferance of its advocates is inversely proportioned to the
evidence in its support.

As a result of extensive modern experiments and discussion, biologists
have grown very cautious, and are by no means so positive as they were
twenty years ago in affirming just _how_ species have come into
existence. Echoes of this old controversy between the two leading
schools of biologists are occasionally heard; but the enthusiasm with
which they set out a half century ago to solve the riddle of plant and
animal life has largely given way to a purpose to discard speculation
and patiently to observe and record actual facts. For with natural
selection discredited in the house of its friends, and Lamarckianism
under grave suspicion from want of a single well authenticated example,
it is hard to see what there is left of the biological doctrine that
has so dominated scientific thought for a half century. If each of these
opposed schools of scientists are right in _what they deny_, the whole
theoretical foundation for the origin of new kinds of animals and plants
is swept away,--absolutely gone. For if an individual really cannot
transmit what he has acquired in his lifetime, how can he transmit what
he has not got himself, and what none of his ancestors ever had? And if
natural selection cannot start a single organ of a single type, what is
the use of discussing its supposed ability to improve them after the
machinery is all built?