“There is grandeur in this view of life, with its several powers, having been originally breathed into a few forms or into one; and that whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.”
In this last sentence of his landmark 1859 publication The Origin of Species, Charles Darwin provided us the basis for his remarkable insights.
His theory of evolution by natural selection is based on ‘randomly varying hereditary elements,’ as described by biologist Richard Dawkins. We now know that those hereditary elements are made up of units of DNA, and in the process of high fidelity copying required for life, imperfections or genetic modification occurs, which natural selection acts upon and results in the amazing biological diversity we see around us.
Advances in molecular biology and in DNA sequencing are enabling scientists to trace the genetic continuity and common ancestry of all species now living on earth (see Ayala, 2009). These advances, combined with morphological data, have produced many evolutionary trees describing the evolutionary history of animals, plants, and microbes; and a recent study provided the first attempt of a complete tree of life.
The first draft of the tree of life is comprised of about 2.3 million named species on the planet
Besides our DNA being the result of billions of years of modification of our ancestral lineage, we also have ‘foreign’ DNA that came from insertion through horizontal transfer. We know that some eight percent of our DNA came from viral infections resulting in DNA from those viruses being integrated into our genome at various times throughout our evolution. This viral DNA has been linked to several attributes, including the development of the mammalian placenta. It is also reported that other microorganisms are an additional source of horizontally transferred DNA residing in our genome.
DNA derived from viruses has been also been reported in plants, and most intriguingly, the DNA from the soil bacterium Agrobacterium tumefaciens has been found in traditionally bred sweet potatoes. This is the same bacterium used as a vector by biotech seed companies to transfer desired genes into plants, and now it is found that transgenic DNA is a natural feature of the domesticated sweet potato gene pool. The authors note “Our finding, that sweet potato is naturally transgenic while being a widely and traditionally consumed food crop, could affect the current consumer distrust of the safety of transgenic food crops.”
As with many other advances derived from studying the world around us, we have learned a lot about DNA, genes and genomes, and have applied that knowledge for our benefit, especially in medicine and agriculture. Genetic modification, including horizontal gene transfer, is the foundation of biodiversity, and its adoption as a tool of plant breeding mimics in a more precise manner what nature has been doing on a large scale for some four billion years.
Animals and plants have evolved by vertical inheritance of genetic modifications and by horizontal gene transfer. In the case of humans, we appear to be a genetically modified, transgenic chimera. You might conclude that we have met the enemy and it is us, or (my preference) raise a toast – All hail GMOs!
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Darwin, C. 2003. The Origin of Species (1859) and The Voyage of the Beagle (1839). New York, NY: Everyman’s Library, Alfred A. Knopf.
Ayala, F.J. 2009. Molecular Evolution. In M. Ruse & J. Travis (Eds.), Evolution: the First Four Billion Years (pp.132-151). Cambridge, MA: Belknap Harvard.
Tree of Life Home Interactive Site
Dawkins, R. 2004. The Ancestor’s Tale: A Pilgrimage to the Dawn of Evolution. Boston, MA: Houghton Mifflin.