Seite - 381 - in The Origin of Species

AFFINITIES OF EXTINCT SPECIES 381 from the continued effects of extinction and divergence of character, has become divided into several sub-families and families, some of which are supposed to have perished at different periods, and some to have endured to the present day. By looking at the diagram we can see that if many of the extinct forms supposed to be imbedded in the successive formations, were discovered at several points low down in the series, the three existing families on the uppermost line would be rendered less distinct from each other. If, for in- stance, the genera a\ d", a", /", »^^ »»", 7n', were disinterred, these three families would be so closely linked together that they probably would have to be united into one great fam- ily, in nearly the same manner as has occurred with rumi- nants and certain pachyderms. Yet he who objected to con- sider as intermediate the extinct genera, which thus link together the living genera of three families, would be partly justified, for they are intermediate, not directly, but only by a long and circuitous course through many widely dift'ercnt forms. If many extinct forms were to be discovered above one of the horizontal lines or geological formations—for in- stance, above No. VI.—but none from beneath this line, then only two of the families (those on the left hand, a\ &c., and fc," &c.) would have to be united into one; and there would remain two families, which would be less distinct from each other than they were before the discovery of the fossils. So again if the three families formed of eight genera (a" to *»"), on the uppermost line, be supposed to differ from each other by half-a-dozen important characters, then the fami- lies which existed at the period marked VI. would certainly have differed from each other by a less number of char- acters; for they would at this early stage of descent have diverged in a less degree from their common progenitor. Thus it comes that ancient and extinct genera are often in a greater or less degree intermediate in character between their modified descendants, or between their collateral relations. Under nature the process will be far more complicated than is represented in the diagram; for the groups will have been more numerous; they will have endured for extremely