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 former years 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 at all times overmastered 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 young, budding twigs; and this connection 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 the other branches; so with the species which lived during long-past geological periods, very few have left living and modified descendants. From the first growth of the tree, many a limb and branch has decayed and dropped off; and these fallen 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 in a fossil state. As we here and there see a thin straggling branch springing from a fork low down in a tree, and which by some chance has been favoured and is still alive on its summit, so we occasionally see an animal like the Ornithorhynchus or Lepidosiren, which in some small degree connects by its affinities two large branches of life, and which has apparently been saved from fatal competition by having inhabited a protected station. As buds give rise by growth to fresh buds, and these, if vigorous, branch out and overtop on all sides many a feebler branch, so by generation I believe it has been with the great Tree of Life, which fills with its dead and broken branches the crust of the earth, and covers the surface with its ever-branching and beautiful ramifications.
When asked whether or not we are Marxists, our position is the same as that of a physicist, when asked if he is a “Newtonian” or of a biologist when asked if he is a “Pasteurian.”There are truths so evident, so much a part of the peoples’ knowledge, that it is now useless to debate them. One should be a “Marxist” with the same naturalness with which one is a “Newtonian” in physics or a “Pasteurian.” If new facts bring about new concepts, the latter will never take away that portion of truth possessed by those that have come before.Such is the case, for example, of “Einsteinian” relativity or of Planck’s quantum theory in relation to Newton’s discoveries. They take absolutely nothing away from the greatness of the learned Englishman. Thanks to Newton, physics was able to advance until it achieved new concepts of space. The learned Englishman was the necessary stepping-stone for that.Obviously, one can point to certain mistakes of Marx, as a thinker and as an investigator of the social doctrines and of the capitalist system in which he lived. We Latin Americans, for example, cannot agree with his interpretation of Bolivar, or with his and Engels’ analysis of the Mexicans, which accepted as fact certain theories of race or nationality that are unacceptable today.But the great men who discover brilliant truths live on despite their small faults and these faults serve only to show us they were human. That is to say, they were human beings who could make mistakes, even given the high level of consciousness achieved by these giants of human thought.This is why we recognize the essential truths of Marxism as part of humanity’s body of cultural and scientific knowledge. We accept it with the naturalness of something that requires no further argument.
Long before there were effective treatments, physicians dispensed prognoses, hope, and, above all, meaning. When something terrible happens-and serious disease is always terrible-people want to know why. In a pantheistic world, the explanation was simple-one god had caused the problem, another could cure it. In the time since people have been trying to get along with only one God, explaining disease and evil has become more difficult. Generations of theologians have wrestled with the problem of theodicy-how can a good God allow such bad things to happen to good people? Darwinian medicine can't offer a substitute for such explanations. It can't provide a universe in which events are part of a divine plan, much less one in which individual illness reflects individual sins. It can only show us why we are the way we are, why we are vulnerable to certain diseases. A Darwinian view of medicine simultaneously makes disease less and more meaningful. Diseases do not result from random or malevolent forces, they arise ultimately from past natural selection. Paradoxically, the same capacities that make us vulnerable to disease often confer benefits. The capacity for suffering is a useful defense. Autoimmune disease is a price of our remarkable ability to attack invaders. Cancer is the price of tissues that can repair themselves. Menopause may protect the interests of our genes in existing children. Even senescence and death are not random, but compromises struck by natural selection as it inexorably shaped out bodies to maximize the transmission of our genes. In such paradoxical benefits, some may find a gentle satisfaction, even a bit of meaning-at least the sort of meaning Dobzhansky recognized. After all, nothing in medicine makes sense except in the light of evolution.