Recent genetic discoveries demonstrate that Darwin's 'tree of life'
theory of evolution is wrong and it's time to move on, argues Didier
Raoult.
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
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.
Chimeras
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 per cent of the genetic sequences found in the samples from the
environment and from faeces analysed in metagenomic studies belong to
the three domains of microbes currently recognised in the tree-of-life
framework — bacteria, archaea, and eukaryotes. Viruses contain another
15 to 30 per cent 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.
Dogma
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, 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 realised.
About the author: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.