Page 212 - The Evolution Impasse 2

210 Tetrapod Finger Structure, The

ge nus (plu ral gen era) THEORY
spe cies
A hy poth e sis that can be sup port -
Most bi ol o gists to day ac cept the
ed with large num bers of ob ser va -
ex is tence of five sep a rate king doms.
tions and ex per i ments is known as a
In ad di tion to the plant and an i mal
the o ry. To put it an oth er way, a the o -
king doms, they re gard fun gi, mon -
ry is a deep-root ed hy poth e sis.
era (sin gle-celled or gan isms with no
However, al though a the o ry is prov -
cell nu cle us, such as bac te ria) and
en with ex per i ments, it may al so be
pro tis ta (cells with a nu cle us, such as
dis proved.
al gae) as sep a rate king doms.
For ex am ple, the claim that "The
The most im por tant of these is
at om is the small est known com po -
with out doubt that an i mal king dom.
nent of mat ter," known as Dalton's
The ma jor di vi sions with in the an i -
atom ic the o ry, to day has lost all va -
mal king dom are its var i ous phy la.
lid i ty. 240 Advances in sci ence and
In the clas si fi ca tion of these phy la,
tech nol o gy have re vealed the ex is -
their dif fer ing bod i ly struc tures are
tence of much small er par ti cles than
con sid ered. Arthropods, for ex am -
the at om and even the pro ton, such
ple, con sti tute a sep a rate phy lum,
as the quark.
and all the crea tures with in that phy -
A sci en tif ic the o ry is an at tempt
lum have a sim i lar body plan. The
to ex plain cer tain phe nom e na oc cur -
phy lum known as Chordata con sists
ring in na ture. A fre quent ly oc cur -
of crea tures with a cen tral nerv ous
ring phe nom e non may be ex plained
sys tem. All the an i mals fa mil iar to
in terms of a the o ry, a fact, or a law.
us such as fish, birds, rep tiles and
Gravity, ex am ple, is a fact. Even if
mam mals are in clud ed in the ver te -
we can not per ceive grav i ty di rect ly,
brate cat e go ry, a sub di vi sion of the
we can still see its ef fect when we
Chordata.
drop some thing. There is al so a the -
o ry of grav i ty that an swers the ques -
tion of how this takes place. Even if
TETRAPOD FINGER
we do not know ex act ly how grav i ty
STRUCTURE, THE
works, there are the o ries that seek to
—See, Five Digit Homology. ac count for it. The law of grav i ty for -
mu lat ed by Isaac Newton is one
such.

The Evolution Impasse II