Origins of species
The "Tree of Life" by Charles Darwin and others
Phylogeny and various "trees of life:"
"Phylogeny" is a study of how species of life are related -- the genealogy of species. A main concept found in the theory evolution is that, at any time in the past, species developed from older species as a result of natural selection driven by environmental stressors and perhaps by other factors.
The use of a tree with a trunk and branches to symbolize the evolution of species a long history, dating from the start of the 19th century. Using this symbol, the first form of life is located at the bottom of the trunk. The branches symbolize the individual species as they first appeared in the biological record, and later developed into other related species.
One principle that is implied by the tree of life is the concept of common ancestors. Any two leaves on a tree can be traced back to separate twigs, and then to one or two branches, and finally back to the trunk. Similarly, the ancestors of any two species can be traced back to a common ancestor species that they have in common. So, for example, humans and chimpanzees can be traced back to their common ancestor. So can whales and dinosaurs, or dogs and sponges, etc.
As Graham Lawton explained in his article "Uprooting Darwin's tree:"
"Ever since Darwin, the tree has been the unifying principle for understanding the history of life on Earth. At is base is LUCA. the Last Universal Common Ancestor of all living things, and out of LUCA grows a trunk which splits again and again to create a vast, bifurcating tree. Each branch represents a single species, branching points are where one species becomes two. Most branches eventually come to a dead end as species go extinct, but some reach right to the top -- these are living species. The tree is thus a record of how every species that ever lived is related to all others right back to the origin of life." 1
Some early "trees of life" were:
- 1891: 2 Augustin Augier, a French botanist, is believed to have published the first "tree of life" to demonstrate his concept of the relationships among plant species. He assumed that God created the various species at different times. Augier had deviated from the biblical creation story in the early chapters of Genesis which described a variety of plants and animals having been created within a few days.
- 1809: Jean-Baptiste Lamarck published the first tree of life involving animals in his book Philosophie Zoologique. It was an inverted tree with worms at the top and mammals -- including humans -- at the bottom. He did not believe that all life evolved from a single organism; he believed that different species could be grouped into separate parallel lines that evolved over time from simple to complex forms.
- 1837: 3 Charles Darwin wrote this "tree of life" in his personal notebook with the caption:
"I think case must be that one generation should have as many living as now. To do this and to have as many species in same genus (as is) requires extinction . Thus between A + B the immense gap of relation. C + B the finest gradation. B+D rather greater distinction. Thus genera would be formed. Bearing relation to ancient types with several extinct forms."
- 1844: 4 An anonymous author published a book in England titled: "Vestiges of the Natural History of Creation" and contained an elementary tree diagram showing how fish (F) first branched from the main evolutionary path at point "A", followed in turn by reptiles (R) and birds (B). The main path continued to produce mammals (M), including humans.
- 1959: 4 Charles Darwin published his book: "On the Origin of Species by Natural Selection." It included this tree of life as its only image.
- 1866: 4 Ernst Haeckel published his version of a tree of life in his book
"Generelle Morphologie der Organismen." It shows an early division of life forms into three kingdoms: Plantae (all living and extinct plants), Protista (a collection of about 35 simple life forms that are either single-celled or multicelled without specialized tissues) and Animalia (the animal kingdom).
The following information sources were used to prepare and update the above
essay. The hyperlinks are not necessarily still active today.
- Graham Lawton, "Uprooting Darwin's tree," New Scientist, 2010-JAN-24, Pages 34 to 39.
"Origins of the tree of life," ChickenOrEggBlog at: http://chickenoreggblog.wordpress.com/
- "File: Darwin tree.png," Wikimedia, at: http://commons.wikimedia.org/
- "Tree of life (science), Wikipedia, at: http://en.wikipedia.org/