[Viewpoint] Life after DarwinMany Greek philosophers perceived the world to be in perpetual motion - a process of constant evolution. In Charles Darwin’s world, however, creationism set the rules for science. So, underpinning his theory of evolution is the literal interpretation of the Bible that dominated his era, combined with Aristotle’s vision of nature as definitively fixed.
Darwin, together with J. B. Lamarck, promoted a vision of a changing world, while upholding the idea that organisms evolved from a single root - a position held by Adam and Eve in the creationist worldview, and taken over in the modern era by the Last Universal Common Ancestor (LUCA). And from that remnant of the biblical story of creation sprung the notion of a tree of life, alongside major concepts such as gradualism and the idea that minor selection pressures can, over time, have a profound effect on improved fitness.
Darwin’s vision of the world deeply influenced biology in the 20th century, despite persistent questions posed by factors such as lateral gene transfer, neutral evolution and chaotic bottlenecks in natural selection. But recent genetic research unequivocally refutes this worldview.
Life is primarily the expression of the information contained in genes. All living organisms appear as mosaics of genetic tissue, or chimeras, suggesting that no two genes have the same evolutionary history. This framework is incompatible with the tree-of-life representation. Rather, it resembles a rhizome - an underground stem that sends out roots and shoots that develop into new plants.
Indeed, we now know that the proportion of genetic sequences on earth that belongs to visible organisms is negligible. Furthermore, only 15 percent of the genetic sequences found in the samples from the environment and from feces analyzed in metagenomic studies belong to the three domains of microbes currently recognized in the tree-of-life framework - bacteria, archaea and eukaryotes. Viruses contain another 15 to 30 percent of these genetic sequences.
The unidentified genetic sequences pose a problem because it is not known whether vehicles other than viruses, bacteria, archaea, and eukaryotes exist. Conversely, we know that new genes, designated orphan genes, or ORFans, are commonly created by gene duplication, fusion or other unknown mechanisms. Yet, according to Darwin’s tree-of-life concept, this phenomenon would be impossible.
Human cells comprise genes of eukaryotic, bacterial, archaean and viral origin. As this chimerism increases, it occasionally integrates genes from microbes that live within the human body - as happens when a human is infected by herpesvirus 6. Once integrated in a person’s genome, these genes can be transmitted from parent to child, making microbial genes their “grandfathers.”
This transfer of genetic sequences from parasites to hosts could involve hundreds of genes for a bacterium in different hosts. For example, if the bacterium Wolbachia’s genes are integrated by different hosts, such as spiders, insects or worms, the hosts’ offspring are also descendants of Wolbachia.
Darwin’s theory is further used to support the belief that ancient humans - Neanderthal, Cro-Magnon, and Denisova - did not mix. In fact, based on Darwin’s assumptions, most anthropologists claim that modern humans were simply descended from Cro-Magnons, who had exterminated their less-fit adversaries. Given this supposition, a single name, Homo sapiens, is used for both modern humans and the preferred ancestor, Cro-Magnon. But we now know that modern humans are chimeras of these three ancient humans.
This understanding also refutes the legend of Mitochondrial Eve, the woman from whom all humans supposedly descend on their mother’s side. Research on the human leukocyte antigen genes, which are involved in the human immune response, shows that such a common ancestor could not have existed; this group of genes derives from those of all three known ancient humans.
Genetic research, in particular, must be free to find new models to explain, and enhance, 21st-century scientific discovery. Today, Darwin’s theory of evolution is more a hindrance than a help, because it has become a quasi-theological creed that is preventing the benefits of improved research from being fully realized.
*The author is the director of the Research Unit in Infectious and Tropical Emergent Diseases at the University of the Mediterranee in Marseille.
By Didier Raoult