The Presidential Address.
79
reconstruct genealogies from the surviving remnants of past
faunas and floras. For the term "affinity" we may now
substitute the expression, blood-relationship. Thus, taking
any group of allied forms, such as the species of a genus, we
say that these have descended from a common ancestral form
now extinct. The wider the group which we are considering
the further back in time should we have to go to arrive at
the point from which the various forms composing the group
diverged ; in other words, the degree of difference between
species is a measure of the amount of their divergence from
a common parent. The science of Palaeontology, which deals
with the life of the past as preserved to us in fossil remains,
becomes linked by inseparable bonds to Taxonomy. It is to
the geological record that we have to appeal to fill up those
links which are necessary for the completion of our pedigrees.
How vastly increased in importance becomes the determina-
tion of true morphological affinity—with what surpassing
interest does Homology become endowed—when we know that
the structural resemblance of two animals, however externally
disguised, is due to community of descent from an ancestor
that lived in the remote ages of geological antiquity.
Until the publication of the 'Origin of Species' geologists
had never fully realised the fact that their fossil collections
represented but an infinitesimal fraction of the whole number
of animals and plants that had peopled the earth from the
earliest times. Darwin says on this point:—" I look at the
geological record as a history of the world imperfectly kept,
and written in a changing dialect; of this history we possess
the last volume alone, relating only to two or three countries.
Of this volume, only here and there a short chapter has been
preserved; and of each page, only here and there a few
lines."14 "The crust of the earth, with its imbedded
remains, must not be looked at as a well-filled museum, but
as a poor collection made at hazard and at rare intervals.''15
When, from the standpoint of modern Geology, we consider
how small is the chance of the prreservation of an animal or
plant in the state favourable for fossilization, and when we
14 ' Origin,' 6th ed., p. 289. 15 Ibid., p. 427.