MARSEILLE – Many 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 (the view that speciation does not occur abruptly) 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 twentieth 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% 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 15-30%
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 ORFans (“orphan genes”), 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.
Moreover, certain viruses’ size and
genetic repertoire is comparable with that of bacteria, archaea, or small
eukaryotes. Indeed, the life of giant viruses is as complex as that of
like-sized microorganisms.
But the current classification of the
domains of life is based on the ribosome – the production apparatus of proteins
– which does not exist in these viruses. Without ribosomes, traditionalists
say, viruses cannot be considered biological entities comparable to other
microbes. But that is pure dogma; these viruses are akin to the other microbes.
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, twenty-first-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.
Didier Raoult is Director of the Research Unit in Infectious and
Tropical Emergent Diseases, collaborating with CNRS (National Center for
the Scientific Research), IRD (Research for the Development Institute), and the
University of the Méditerranée in Marseille.