' habitants. So many operative 'causes, totally different from
any that we are now acquainted with, must have been em-
ployed in setting on foot that series of phenomena which wel
term the course of Nature, that we are in danger of losing I
ourselves in doubts and ~ conjectures when we adveft-to the I
subject, and it requires the g r^ te ^ t care to avoid wandering
into wild and visionary speculations. It is only by a careful
survey of actual facts, and an accurate analysis^ o f their relations,
that any light can be thrown on the history of organized
s fe c i^ , and the circumstances' and conditioijsjoftheir
origin and early existence. In attempting to follow, particular
inquiry-above 'suggested,. it- will be necèssary to take
into consideration a gréât number of facts, to examine accurately
their bearings, and |o collect the inferences which arise
from their comparison.
Linnæus maintained, th a t in every species o f plants as .well
as of animals, only one pair was originally p ro d u c e d ^ Fnum
individuum ex hermaphroditis et unicum par reliquoçuro vi-J
ventium fuisse primitùs creatum, sgna ra tira d e tu r clarissimè
ostendëre.”
He defended this position by a very ingenious argument-
of which the following is neariyjhe substancerî^r-
Experience proves to^us that every'family rQf human or
other living creatures has a tendency to multiply,hand^thgt
the progeny naturally becomes more numerous a f every îsuc-
cessive generation, • •
If we follow the history of the race in im a g in a tS h ^ tf^ ii^
Hie line perpetually onwards,- we find the. niimbet' greater at
each subsequent step in the series, than in -the step im.
mediately preceding, and we perceive -the number of individuals
in eaeh kind to be greater to-day than it was yesterday.
If now we turn our thoughts in the opposite direction, and
follow the ascending line, we dbserve each species reduced at
every step to a smaller number; many deriving their existence
from few, and these few from still - fewer : nor is there any
term at which we find reason to stop* until we come to a single
pair.
Linnæus afterwards proceeded to shew, that Nature has
provided such means of multiplication and dispersion, as
seem only requisite on the hypothesis adopted by him.
- As examples? o f; the multiplication of species, he remarks
that one poppy-seed has been- known to produce a plant containing*
32>$1|0'&eed$, and one ieedo^ a good soil,
to multiply 40,3‘2©i fold.
5 -These considerations are-not without some degree of force*
at least they seem to render one conclusion more probable
than another. But nothingi altogether satisfactory can be
derived from so speculative an argument.
: Perhaps there issue other way of investigating the history
of particular speciesj and throwing some light on the inquiry,
whether each tribe is,.derived from one or from many originals,
than by collecting, the: facts which.relate to their multi
plication and dispersion/ and tracing the distribution of
genera and* species* «sen different - parts- of the earth. If it
should appear, on examination, that animals or plants of each
kind have'theirexistence, in general, in those tracts only to
which itiis probable they may have wandered, or whither they
may have been conveyed, by .accidental means, from some
lüngle, point—a point which may be looked -upon as the primitive
or original- seat of the tribe—-there will be. a sufficient
reason for believing*; the whole number belonging to each
species respectively,,to have descendèff drom a single origin.
But if, on the contrary, organized beings of the same species
are met with in places remote from each other, effectually
separated by vast distances/; or by natural barriers, which
the locomotive powers bestowed by Nature ft on particular
tribes cannot have ,enabled them to pass ; and if such • examples
are not rare exceptions to a general law, but matters
óf frequent observation, it must be allowed that creatures of
the same kind had; probably distinct and separate origins.
It will be necessary to pursue the inquiry suggested by
this observation, under separate beads, as^.it relates to the
different orders of organized beings, v I shall begin with the
dispersion of plants/, and proceed then to the lower, and
afterwards to the higher departments, as they are termed, of
animated nature.