On the Origin of Species

by Charles Darwin

This basic image is powerfully represented in the early chapters of Genesis, when one of Adam’s first tasks is to name the plants and animals in Eden.

The relationship between religious belief and evolutionary theory has been an ongoing theme, not least in our own era, during which creationism and the doctrine of ‘intelligent design’ are powerful forces, especially in the USA and in Muslim countries.

But many commentators, both during Darwin’s lifetime and since, have insisted that science and religion relate to two areas of human experience, and therefore can be reconciled.

The Tree of Life which Darwin illustrated is still essentially the one which is presented in natural history museums around the world, and descent with modification provides the framework within which most evolutionary biology has been conceived ever since Origin.

This research reinforced Darwin’s vision of the Tree of Life, but it had little to say directly about the mechanism by which it had evolved.

As many more individuals of each species are born than can possibly survive; and as, consequently, there is a frequently recurring struggle for existence, it follows that any being, if it vary however slightly in any manner profitable to itself, under the complex and sometimes varying conditions of life, will have a better chance of surviving, and thus be naturally selected.

From the strong principle of inheritance, any selected variety will tend to propagate its new and modified form.

Owing to this struggle for life, any variation, however slight and from whatever cause proceeding, if it be in any degree profitable to an individual of any species, in its infinitely complex relations to other organic beings and to external nature, will tend to the preservation of that individual, and will generally be inherited by its offspring.

I have called this principle, by which each slight variation, if useful, is preserved, by the term of Natural Selection, in order to mark its relation to man’s power of selection.

never to forget that every single organic being around us may be said to be striving to the utmost to increase in numbers;

All that we can do, is to keep steadily in mind that each organic being is striving to increase at a geometrical ratio;

This preservation of favourable variations and the rejection of injurious variations, I call Natural Selection.

The affinities of all the beings of the same class have sometimes been represented by a great tree. I believe this simile largely speaks the truth. The green and budding twigs may represent existing species; and those produced during each former year may represent the long succession of extinct species. At each period of growth all the growing twigs have tried to branch out on all sides, and to overtop and kill the surrounding twigs and branches, in the same manner as species and groups of species have tried to overmaster other species in the great battle for life. The limbs divided into great branches, and these into lesser and lesser branches, were themselves once, when the tree was small, budding twigs; and this connexion of the former and present buds by ramifying branches may well represent the classification of all extinct and living species in groups subordinate to groups. Of the many twigs which flourished when the tree was a mere bush, only two or three, now grown into great branches, yet survive and bear all the other branches; so with the species which lived during long-past geological periods, very few now have living and modified descendants. From the first growth of the tree, many a limb and branch has decayed and dropped off; and these lost branches of various sizes may represent those whole orders, families, and genera which have now no living representatives, and which are known to us only from having been found in a fossil state. As we here and there see ...

On the principle of the continued tendency to divergence of character, which was formerly illustrated by this diagram, the more recent any form is, the more it will generally differ from its ancient progenitor.

Therefore I should infer from analogy that probably all the organic beings which have ever lived on this earth have descended from some one primordial form, into which life was first breathed.