This Great Tree of Life diagram is based primarily on the evolutionary relationships so wonderfully related in Dr. Richard Dawkins’ The Ancestor’s Tale. Some secondary branching relationships and ages of common ancestors were gleaned from university and other scholarly websites as well as scientific journals. The smallest branches are purely illustrative; they are intended to suggest the effect of mass extinctions on diversity, and, on a few of the branches, changes in diversity through time. This tree of life diagram is NOT intended to be used as a scholarly reference tool or as a complete picture of life history (only a very few extinct main branches are shown, for example). Instead, it tries mainly to illustrate a great lesson of evolution; that we are related not only to every living thing, but also to every thing that ever lived. Click to view an enlargement of this Great Tree of Life.
‘To make the Great Tree of Life easier to understand, it is drawn from the human, mammalian point of view.’
Distortions and Limitations: In order to make the Great Tree of Life uncluttered and easier to understand, a number of distortions have been purposively built in. First, and most important, this Great Tree of Life is drawn from the human, mammalian point of view. That is why humankind, instead of some other organism, occupies a branch tip at the end of the tree, and why our vertebrate cousins (animals with a backbone) occupy a large part of the tree. This falsely suggests that humans are the ultimate goal of evolution. In fact, if that asteroid or comet that hit the earth 65 million years ago and helped wipe out the dinosaurs, had instead missed the earth, there might not be a dominant, tool-using, space-faring species on earth. Or if one evolved, it might be a dinosaur, not a mammal. Also, the world of bacteria holds far more genetic diversity, and accounts for a vastly larger proportion of biomass than animals do, yet Bacteria occupy only a relatively small portion of the tree. Trees of Life drawn from the bacterial point of view look very different: on these diagrams, the whole world of animals and plants occupy only a tiny part of the tree.
‘If the asteroid which contributed greatly to the mass extinction 65 million years ago had missed the Earth, perhaps the space-faring species on Earth today would be a dinosaur, not a mammal.’
Another limitation of this tree of life diagram is that it suggests life steadily increased in diversity through time, such that the greatest diversity appears to exist at the present time. This is not at all the case in life history, and only appears that way in this diagram because, for space reasons, only a few of the main branches of life that have gone extinct are shown. The evidence suggests that many more branches have gone extinct than exist today. One estimate concludes that 99% of species that have ever existed on earth are now extinct. If the diagram could be drawn to really reflect life history, the greatest diversity in major body plans would probably appear early in the Cambrian Period, around 530 million years ago. Only a few major body plans survived the Cambrian, but these few have evolved into the diversity we have today.
Leer más “Tree Of Life: The History of the World, Visualized”