All Types Seem
J.S. Huxley, Evolution, the Modern Synthesis (Allen & Unwin,
London, 1942), pp. 562, 571.
....And there is no certain case on record of a line showing a high
degree of specialization giving rise to a new type. All new types which themselves are
capable of adaptive radiation seem to have been produced by relatively unspecialized
ancestral lines. ..Evolution is thus seen as a series of blind alleys.
E.S. Russell, "The Diversity of Animals," Acta
Biotheoretica, vol. 13 (Suppl. 1), p. 1.
Existing species represent the terminal twigs of a vast process of
differentiation; each is stamped not only with the characters of the genus, the family,
the order, the class to which it belongs--the characters, that is to say, of the branch
and trunk from which it has sprung. It may proliferate further twigs, producing new
species and possibly even new genera...but there is no possibility of its producing new
branches. That new types of organization, even minor ones, can be evolved from the
specialized end-products of the great evolutionary tree seems a rank impossibility.
G.G. Simpson, The Meaning of Evolution (Bantam
Books, New York, p. 298.
It has been suggested that all animals are now specialized and that the
generalized forms on which major evolutionary developments depend are absent. In fact all
animals have always been more or less specialized and a really generalized living form is
merely a myth or an abstraction. It happens that there are still in existence some of the
less specialized, that is, less narrowly adapted and more adaptable, forms from which
radiations have occurred and could as far as we can see occur again. Opossums are not
notably more specialized now than in the Cretaceous and could almost certainly radiate
again markedly if available spaces were to concur again. ...