July, 1925 
The Queensland Naturalist. 
27 
We know of the mechanism behind organic- 
evolution, and we ma.y best summarise our position with, 
respect to the possibility of Convero’ent-EvoUition in re- 
spect to th(‘ orijiin of the Diprotodont marsupials by 
remarkin': tiiat the existence of such was in all proba- 
bility i>reviously impossible. There is no more romantic 
aspect of biological speculation than that concerned 
with the (dueidation of the j^roblems of distribution, and 
it is largely due to this alluring influence that there has 
been too marked a tendency to allow the imagination to 
run away from scientific control. It is certainly time 
that an Antarctic link with Australia during Tertiary 
times would explain many occurrences of faunal and 
floral forms, but the same argument a])])lies in the case 
of ether theories, say, such as that which would explain 
' tlie reseml)!ances l)etween certain types of fauna and 
flora in the Southern Continents as being due to a migra- 
; tioTi from the North and tlieir pre.servation in the South- 
. era areas, or Avould regard them as persistent represen- 
tatives of a moi*e or less universal stock. It is highly 
r ])robable that no oru* of these tln’ories holds the ground 
^ to the exclusion of the others, and tliat any rigid appli- 
* cation of one theory leads ns from the truth in resi)ecl 
to any particular group. We liave a similar attempt to 
over-ride comidexities in the attempt to decide affinities 
of groups of animals and ])lants. ]\Iany treatises in an 
attempt to g’raphically illustrate tlie resemblance of 
various groups — I refer to classes and families, ete., — 
make irse of phylogenetic trees, in which the various 
brandies represent individual classes, families, etc. The 
idea serves a good jiurpose in thal respect, but unfortu- 
nately there is too often a tendency for iieojile to treat 
sudi graphic Iveys in a too literal manner, and to interiiret 
them as a time-table indicating the relative times of ap- 
pearance of tlie groups by noting the point on the main 
stem from which tlie liranches arise. In other Avords, 
organic eAmlution is regarded as Avorking in a patently 
mechanical fashion. It is much more probable that com- 
])Iexities and A*agaries liidc the ju’ocess of evolution from 
onr gaze. Such iieople are satisfied to explain the evohi- 
lioii of (dasses Avliile tlie origin ot sjAecies still represents 
a problematical question. Much the same position ob- 
tains AAUth resjAoet to the jAroblems of distribution. Tn 
the first place Ave must recognise that a knoAvledge of 
