Page - 515 - in The Origin of Species

RECAPITULATION AND CONCLUSION SIS mediate position in the chain of descent. The grand fact that all extinct beings can be classed with all recent beings, naturally follows from the living and the extinct being the offspring of common parents. As species have generally diverged in character during their long course of descent and modification, we can understand why it is that the more ancient forms, or early progenitors of each group, so often occupy a position in some degree intermediate between ex- isting groups. Recent forms are generally looked upon as being, on the whole, higher in the scale of organisation than ancient forms ; and they must be higher, in so far as the later and more improved forms have conquered the older and less improved forms in the struggle for life; they have also generally had their organs more specialised for different functions. This fact is perfectly compatible with numerous beings still retaining simple and but little improved struc- tures, fitted for simple conditions of life; it is likewise com- patible with some forms having retrograded in organisation, by having become at each stage of descent better fitted for new and degraded habits of life. Lastly, the wonderful law of the long endurance of allied forms on the same conti- nent,—of marsupials in Australia, of edentata in America, and other such cases, is intelligible, for within the same coun- try the existing and the extinct will be closely allied by descent. Looking to geographical distribution, if w^e admit that there has been during the long course of ages much migra- tion from one part of the world to another, owing to former climatal and geographical changes and to the many occa- sional and unknown means of dispersal, then we can under- stand, on the theory of descent with modification, most of the great leading facts in Distribution. We can see why there should be so striking a parallelism in the distribution of organic beings throughout space, and in their geological succession throughout time ; for in both cases the beings have been connected by the bond of ordinary generation, and the means of modification have been the same. We see the full meaning of the wonderful fact, which has struck every traveller, namely, that on the same continent, under the most diverse conditions, under heat and cold, on mountain and