Reflection paper 2

Medical Hypotheses (2005) 65, 868–872

http://intl.elsevierhealth.com/journals/mehy

Origin and evolution of viruses: Escaped
DNA/RNA sequences as evolutionary
accelerators and natural biological weapons
a,*
Ivan Bubanovic , Stevo Najman b, Zlatibor Andjelkovic c

a
Department of Obstetrics and Gynecology, Medica Centre, Novosadska 1/c, 18000 Nis, Serbia,
Serbia and Montenegro
b
Institute of Biology, Medical Faculty, University Medical School, Nis, Serbia and Montenegro
c
Institute of Histology, Medical Faculty, Pristina, Kosovska Mitrovica, Serbia and Montenegro

Received 15 April 2005; accepted 12 May 2005

Summary Knowledge of the origin and evolution of viruses could provide a better understanding of a number of
phenomena in the field of evolution such as the origin and development of multi-cellular organisms, the rapid
diversification of species over the last 600–700 million years and the lack of transitional forms in the evolution of species
(‘‘missing links’’) etc. One of the possible effects of escaped DNA/RNA sequences or viruses on the evolution of multi-
cellular organisms, especially vertebrates, could be the phenomenon of horizontal transmission and dissemination of
genes. Interestingly, if so, this effect could be considered as a model of primeval and natural genetic engineering. Other
possible links between the evolution of multi-cellular organisms and viruses are connected with the fact that viruses
represent the source of different forms of selective pressure such as epidemics of infectious diseases, autoimmunity,
malignant alteration, reproductive efficiency, etc. At the same time, these two models of ‘‘long-term evolutionary
relations’’ could represent ‘‘key factors’’ in the evolution between viruses and multi-cellular organisms. The capability
of a genome to produce and emit DNA/RNA sequences or de novo created viruses which can be a vector of genes
horizontal transmission and/or cause selective pressure on concurrent or predator species gives a new characteristic to
viruses – the possibility of their acting as natural biological weapons. Finally, possibly evolutionary advantages of this
genome capability could be one of explanations for the phenomena such as genome instability and its ability to emit
DNA/RNA sequences and/or de novo created viruses, as well as evolutionary conservation of this unique phenomena.
c 2005 Elsevier Ltd. All rights reserved.

The origin and evolution of viruses mostly unknown. Our knowledge concerning their
origin is lost in a sea of conjecture and specula-
In contrast to other microbes and multi-cellular tions, hardly supported at all with precise scientific
organisms, the origin and evolution of viruses is evidences. For example, viruses have never been
detected as fossil particles, probably because they
* Corresponding author. Tel.: +381 1849 178. are too small and too fragile to succumb to fossil-
E-mail address: ibubanovic@yahoo.com (I. Bubanovic). ization processes. Even in fossilized biological

0306-9877/$ - see front matter c 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.mehy.2005.05.038

Origin and evolution of viruses 869

materials such as plant leaves or insects in amber, tion of evolutionary processes, which could result
preserved nucleic acid sequences of viruses have in rapid diversification of species and sometimes
never been detected. Hence, evolutionists are lim- quicker and better adapting to environmental con-
ited in their ability to precisely reconstruct an evo- ditions; (iii) the possibility that de novo created
lutional history of viruses. However, in spite of all viruses can act as natural biological weapons
the difficulties in understanding their origin and against predator and/or concurrent species.
evolution, several theories more or less success- There are a number of complex molecular life
fully explain the basic observed facts [1–3]. forms that blur the boundaries between cells and
Due to the fact that the genome of viruses viruses. Also, there are pieces of self-replicating
underlies mutation and genetic recombination, genetic material found in bacteria, e.g., episomes,
viruses probably evolve according to a form of nat- which evolve independently of their hosts, and can
ural selection, very similar to that governing other even move from one host to another – but carry
living things. It seems that this simple fact may genetic information that may be toxic or benefi-
well provide enough support for scientific accept- cial, even essential, to their host. In the case of
ability of several commonly discussed hypotheses the beneficial role of episomes, many bacteria
on virus origin and evolution. Currently, there are would be unable to reproduce at all without them.
three such hypotheses. The first hypothesis is the Episomes are, in many ways, quite similar to
so-called theory of ‘‘regressive evolution’’, which viruses – except that they only reproduce them-
proposes that viruses descend from free-living selves when their hosts do, whereas viruses repro-
and more complex parasites. According to this the- duce themselves hundreds of times, causing
ory, ancestral viruses developed a growing depen- disease. According to this way of thinking, viruses
dence on host-cell intracellular ‘‘machinery’’ probably co-evolve with their hosts, like any ‘‘good
through evolutionary time, while retaining the abil- parasite’’. There appears to be quite a lot of justi-
ity to auto-replicate, like mitochondria that have fication for this idea, especially from studies of
their own genetic information and replicate on viruses such as papilloma viruses, endogenous ret-
their own [2–4]. The second hypothesis is the so- rovirus-like sequences in animal genomes, and her-
called theory of ‘‘cell origin’’, which assumes that pes viruses. For example, the divergences of
viruses reflect their origin from cell DNA and/or primates and of birds related to chickens have been
messenger RNA, which acquired the ability to traced by comparing the types and sequences of
auto-replicate, create extracellular virions, exist retroviral-derived sequences in their genomes. It
and function independently. Finally, there is the has also been repeatedly shown that the closest
theory of ‘‘independent’’ or ‘‘parallel’’ evolution relatives of human papillomavirus types infecting
of viruses and other organisms, which assumes that particular tissue types (e.g., cutaneous wart types,
viruses appeared at the same time as the most genital mucosal types) are those viruses infecting
primitive organisms [1,3,4]. similar tissue types in other primates, indicating
Whatever the advantages and disadvantages of that these tissue preferences were well established
each theory are, the ability of every cell (excluding before the divergence of humanoid apes from the
cells without a nucleus, e.g., the erythrocytes of primate line [1,3,4].
mammals) to release DNA/RNA sequences or de
novo created viruses is unique and amazing. At
the same time, the cell’s ability to release DNA/ Viruses as evolutionary accelerators
RNA sequences shows a high level of evolutionary
conservation. These facts might be well enough The model of living beings evolving based on gen-
motifs for identification of positive selective pres- ome changes and the ability to adapt to positive
sure that could be linked with this genome ability, and/or negative selection pressures is widely ac-
as well as a highly important thesis for better cepted among evolutionists. However, it is hard
understanding of origin and evolution of viruses, to imagine that the evolution of life is based on
and even life as we know it [3–5]. Several factors accidental and isolated gene mutations and that
of positive selective pressure could play important this model of evolution finally brought about the
role in development and evolutionary ‘‘symbiotic’’ form of life we know today. One of key arguments
linking (conservation) of genome and its ‘‘instabil- against a model of evolution based on the acciden-
ity’’, which is probably responsible for cell ability tal changes of isolated genes is the simple fact that
to emit de novo created viruses: (i) the possibility gene mutation is a relatively rare event and hence,
of horizontal and vertical dissemination of gene according to this model, evolution would be very
blocks, and their incorporation into the cell gen- slow. Many evolutionists argue that life on the
ome of new hosts; (ii) the possibility of accelera- Earth would still be at the bacteria and seaweed

870 Bubanovic et al.

stage, if genetic changes were based only on acci- takes whole blocks of genes and moves them to dif-
dental changes of isolated genes. Considering the ferent locations. These new locations could be
fact that most mutations are sources of negative elsewhere in the same genome or in the genome
selective pressure, the minor percentage of acci- of a different host. One of recombination mecha-
dental mutations of genes that might cause posi- nisms is transduction by viruses that works in both
tive selective pressure, theoretically, could not prokaryotic and eukaryotic organisms. The discov-
result in the evolution of living beings and the ery that large blocks of genetic instructions can
diversity of species that we know today. Certainly, be swapped and transferred among living beings
this opinion does not completely exclude participa- is a clue that the insertion of new genes could be
tion of accidental isolated gene changes in the evo- the mechanism that assists evolution. If viruses
lutionary processes, but the influence of these can transfer eukaryotic genes across species
events on the evolution of life probably is minimal boundaries, and can install their own genes into
and marginal [3,4,6]. their hosts, the case for the new mechanism is even
With the exception of the mutations of isolated stronger. Viruses do just that [1,3,4,6,7].
genes, several different mechanisms can lead to
genome changes. These mechanisms are recombi-
nation, transposition, translocations, inversions,
deletions, duplications, transduction and other Viruses as natural biological weapon
unpredictable, chaotic and yet unremarkable ge-
netic events which, in contrast to mutations, lead From the standpoint of medical science, instabil-
to great changes of genome. Significant genetic ity is a highly undesirable feature of a genome as
changes can probably result in ‘‘great evolutionary it is very often a source of malignant alteration
displacement’’ and acceleration of evolutionary of cells, spontaneous abortion, autoimmunity,
processes. Incidentally, this hypothesis might rep- genetic diseases, emerging and even the re-
resent an acceptable explanation for the many emerging of new viruses. In contrast to this,
‘‘missing links’’ in palaeontology and the state of speaking in a Darwinian sense, the evolutionary
our knowledge regarding the origin of life and spe- advantages of genome instability are probably
cies. Put quite simply, what we call the ‘‘missing more important than potential and real negative
links’’ probably never existed, due to ‘‘rapid’’ consequences of this phenomenon. In addition,
and large-scale changes which, for as yet unknown emitted DNA/RNA sequences and/or de novo cre-
reasons, have implicated, from time to time, every ated viruses can operate as natural biological
living creature in the last billion years. Conse- weapons against predator and/or concurrent spe-
quently, we can conclude that the evolution of liv- cies. This possibility could also be the source of
ing beings probably has not been based on gradual positive selective pressure supporting evolution-
and ‘‘fine’’ passing forms. In this story, viruses ary conservation of features such as genome
could be an important factor in the theory of ‘‘ra- instability and its ability to emit its own se-
pid and big evolutionary steps’’ based on great quences [8–11].
changes of genome. Several mechanisms might be Viruses apparently can, and obviously do, make
included in this evolutionary scheme: (i) horizontal big jumps in hosts every now and then. It seems al-
transmission of genes between individuals of iden- most certain, for example, that arthropods are the
tical or even different species; (ii) vertical trans- original source for a number of virus families
mission of genes and bi-directional vertical infecting insects and mammals – such as the Flavi-
transmission between mother and offspring in viridae – and probably also of viruses infecting in-
viviparous species; (iii) genome destabilization sects and other animals and plants – such as the
and induction of new changes of genome; (iv) Rhabdoviridae and Reoviridae. For example, picor-
increasing genome instability. Finally, the advanta- naviruses of mammals are very similar structurally
ges of the rapid evolution of living beings and a and genetically to a large number of small RNA
possible link of this phenomenon with viruses could viruses of insects and to at least two plant viruses,
be an acceptable explanation for the ‘‘symbiotic’’ and – as the insect viruses are more diverse than
connection of the genomic ability to emit DNA/RNA the mammalian viruses – probably had their origin
sequences and/or de novo created viruses. This in some insect that adapted to feed on mammals
phenomenon could lead to evolutionary conserva- (or plants) at some distant point in evolutionary
tion of genome instability as a universal genome time. The majority of existing viruses relevant to
characteristic [6,7]. humankind are zoonozis. In spite of the fact that
Recombination is a far more powerful way for animals are the source of many viruses pathogenic
DNA to change. This model of genome remodelling to humans, the most important factor in the

Origin and evolution of viruses 871

dissemination of viruses is the fact that humans hunting and killing the two smaller species of
live in a manner which increases the possibility of monkey [16].
transmission of new viruses from their endogen The hypothesis that HIV evolved from SIV is
hosts (animals) to humans. Rodents and arthropods based on the many similarities between these
are also included in transmission of viruses from two viruses, especially at the genetic level. The
one species to another, especially in an urban two viruses are genetically very similar and are
milieu where their vector role is multi-amplified. transmitted in the same way. However, HIV only
Other animals, especially primates, represent causes AIDS in humans and SIV only causes AIDS
important sources of viruses potentially pathogenic in monkeys. The SIV virus, like HIV, is found in
for humans. In this context, we can mention a few blood. This can provide support for the belief
emerging or even re-emerging, new extremely that HIV entered man via monkey’s blood. For
virulent and dangerous viruses which cause dis- this, possible routes include drinking the blood
eases such as Ebola, Marburg and Congo-Crimean of monkeys, eating raw monkeys or perhaps di-
haemorrhagic fever, Hantavirus lung syndrome, rect exposure of humans to monkey blood
Korean haemorrhagic disease, SARS-Co virus, and [13,14,16]. Finally, the possibility of interspecies
of course, HIV1 and HIV2 [1,3,4,7]. sexual transmission cannot yet be excluded.
HIV is important problem for humankind and
also a good example that can support our hypoth-
esis on viruses as natural biological weapons. It is
now generally accepted that HIV is a descendant Conclusion
of simian immunodeficiency virus (SIV). Certain
simian immunodeficiency viruses bear a very close The opinion that viruses simply cause infectious
resemblance to HIV-1 and HIV-2. For example, diseases is over-simplified and archaic. Their role
HIV-2 corresponds to a simian immunodeficiency in nature and their influence on the evolution of
virus found in the sooty mangabey monkey other living things is probably of greater and,
(SIVsm), widely known as the green monkey, even, crucial importance. The ability of a gen-
which is indigenous to western Africa. The more ome to emit de novo created viruses and the evi-
virulent strain of HIV, namely HIV-1, was, until dent evolutionary conservation of this property
very recently, more difficult to place. The closest strongly suggests that emitted DNA/RNA se-
counterpart that had been identified was the sim- quences could be important in the evolution of
ian immunodeficiency virus that was known to in- life. Practically, this means that viruses could
fect chimpanzees (SIVcpz), but there were be important sources of positive selection pres-
significant differences between it and HIV. In sure on certain species, thus opening up the pos-
addition, it was reported that frozen tissue taken sibilities of: (i) horizontal dissemination of genes;
from a chimpanzee carried a simian virus (SIVcpz) (ii) rapid and large-scale evolutionary changes by
which was almost identical to HIV-1. The chim- way of unstable genomes; (iii) a role as biological
panzee came from a sub-group of chimpanzees weapons directed against concurrent and/or
known as Pan troglodytes troglodytes, which were predator species.
once common in west-central Africa. It is claimed
by some researchers that this shows that these
chimpanzees were the source of HIV-1, and that
the virus at some point crossed species from chim- References
panzees to humans. However, it was not necessar-
[1] Margulis L, Sagan D. Microcosmos: four billion years of
ily clear that chimpanzees were the original evolution from our microbial ancestors. University of
reservoir for HIV-1 because chimpanzees are only California Press; 1997.
rarely infected with SIVcpz. Also, there is opinion [2] Desjardins C, Eisen JA, Nene V. New evolutionary
that wild chimps became infected simultaneously frontiers from unusual virus genomes. Genome Biol
with two simian immunodeficiency viruses (SIVs) 2005;6:212–3.
[3] Margulis L. Symbiotic planet: a new look at evolu-
that had ‘‘viral sex’’ to form a third virus capable tion. Basic Books; 2000.
of infecting humans and causing AIDS [12–15]. [4] Margulis L, Sagan D. What is life? University of California
Sharp et al. [16] discovered that the chimp virus Press; 2000.
was an amalgam of the SIV infecting red-capped [5] Vandamme AM. Phylogenetic techniques improve our
mangabeys and the virus found in greater spot- understanding of virus evolution. Infect Genet Evol
2005;5(3):197–200.
nosed monkeys. The authors believe that the [6] Singh ND, Petrov DA. Rapid sequence turnover at an
hybridisation took place inside chimps that had intergenic locus in Drosophila. Mol Biol Evol 2004;21:
become infected with both strains of SIV after 670–80.

872 Bubanovic et al.

[7] Schmid M, Ott G, Haaf T, Scheres JM. Evolutionary [12] Switzer WM, Salemi M, Shanmugam V, et al. Ancient co-
conservation of fragile sites induced by 5-azacytidine and speciation of simian foamy viruses and primates. Nature
5-azadeoxycytidine in man, gorilla, and chimpanzee. Hum 2005;434:376–80.
Genet 1985;71:342–50. [13] Gao F, Bailes E, Robertson DL, et al. Origin of HIV-1 in the
[8] Bubanovic I. Crossroads of extrathymic lymphocytes mat- chimpanzee Pan troglodytes troglodytes. Nature
uration pathways. Med Hypotheses 2003;61:235–9. 1999;397:436–41.
[9] Bubanovic I, Najman S. Failure of anti-tumor immunity in [14] Bailes E, Gao F, Bibollet-Ruche F. Hybrid origin of SIV in
mammals – evolution of the hypothesis. Acta Biotheor chimpanzees. Science 2003;300:1713.
2004;52:57–64. [15] Zhu T, Korber BT, Nahmias AJ, Hooper E, Sharp PM, Ho DD.
[10] Bubanovic I, Najman S. Comparative oncology and com- An African HIV-1 sequence from 1959 and implications for
parative tumor immunology. J Biol Sci 2005;5:114–8. the origin of the epidemic. Nature 1998;391: 594–7.
[11] Bubanovic I. Origin of anti-tumor immunity failure in [16] Sharp PM, Robertson DL, Hahn BH. Cross-species transmis-
mammals. Kluwer Academic/Plenum Publishers/Springer; sion and recombination of ‘‘AIDS’’ viruses. Philos T Roy Soc
2004. B 1995;349:41–7.

Reflection paper 2

More Related Content

What's hot (20)

Similar to Reflection paper 2 (20)

More from Marilen Parungao (20)

Reflection paper 2