The ancient Egyptians populated their vast pantheon of gods and goddesses with an incredible menagerie of animals and birds. From the run-of-the-mill creatures to the exotic—virtually every conceivable beast was venerated by the masses. Monkeys and baboons were also greatly regarded in various roles and contexts throughout Egyptian history. As the representatives of the gods and in their role as pets and helpers, these animals were dear to the people. Quite bizarrely, in addition to being trained to pick fruit and lend a hand in mundane chores; monkeys also formed an elite squad that was every criminal’s worst nightmare! Evidence shows that the primates policed the streets with their human counterparts – much like canine companions of cops today.
A Steatite sculpture of a seated Baboon representing the god of wisdom, Thoth. New Kingdom. Los Angeles County Museum of Art.
Hailing Baboons and Monkeys
The Egyptians were of the view that living beings, both big and small; feathered and scaled, were the repositories of magical powers. Endowed with special capabilities, these creatures were believed to communicate with the gods and perform the role of intermediaries between the multitude of deities and humankind. However, even though animals were considered sacred messengers, the populace did not worship them per se. On the contrary, they paid obeisance to the invisible and supernatural attributes of the deities that they believed manifested in animal form. And so, a range of beasts and birds were heralded in cult centers dedicated to their worship across the land.
The sides of this seat from a group statue are decorated with images of baboons. On the right side, seen here, the animal is shown holding a cosmetic pot or kohl eyeliner. Painted limestone. 18th Dynasty. Egyptian Museum, Cairo.
The advent of baboons in religion can be traced back to the dawn of the Egyptian civilization; and one of the earliest pre-dynastic deities was the baboon god Baba (or Babi) – “Bull of the Baboons” who, it was thought, devoured the innards of the immoral dead. Examples of artistic representations of monkeys and baboons – be they sculptures, reliefs, or paintings – abounded throughout the country. Extant art from the Old and New Kingdom periods portrays the primates in different settings; and monkeys in particular are often shown engaging in human activities including, among other things - harvesting figs, playing musical instruments, dancing and even policing!
That’s not all; monkeys can be seen in winepresses, lending a hand in beer production and rigging and building boats as well. “However, scholars such as Deiter Kessler believe that there were no trained monkeys in ancient Egypt, and that most such scenes have some sort of “religio-theological function”, though particularly on New Kingdom ostraca there may have also been an element of humor,” notes Egyptological scholar, Jimmy Dunn.
This relief from the mortuary temple of Ramesses III shows the king worshipping alongside sacred baboons. Medinet Habu, Theban Necropolis. (Photo: CC by SA 3.0 / Rémih )
The Egyptians regarded monkeys over and above their humorous antics; they considered them as erotic symbols linked to the cycle of birth, death, and rebirth. “Monkeys were evidently closely linked to female sexuality, probably on a less subtle level than the duck or goose. The baboon which, in some instances alternates with the monkey, had the phonetic value “nfr”, a word which cannot always be translated by one equivalent English word. 'Good', 'Beautiful' and the like is the conventional rendering, but the word also implies something dynamic, creative and potent,” writes Dr Lise Manniche.
In spite of their fearsome appearance and unpredictable nature, baboons and monkeys were nurtured as pets, with the latter being imported from Nubia. The Theban Queen Makare, was buried with her favorite female Green Monkey. This species was deified as an aspect of the invisible primeval god, Atum, particularly when depicted shooting with a bow and arrow. Evidence also suggests that these primates were exclusively reared in temples, like many other animals and birds that were associated with, and sacred to, specific deities.
Two men are depicted catching birds, while in the lower register a boy is shown playing with two monkeys. Tomb of Atet, Meidum. Limestone with inlays. 4th Dynasty. Glyptotek, Copenhagen.
King’s Connect with the Hamadryas
Experts opine that unlike baboons, monkeys were not worshipped in Egypt whilst they were alive. The animal was deified post mortem following its mummification, before which they spent their lives in temple sanctuaries. The ritual interment of monkeys in large necropolises dedicated to them and also in the burials of nobles and kings was a common practice.
Baboons depicted in art were predominantly the hamadryas (Papio hamadryas), a species from the Old World monkey family. Hamadryas baboons were associated with Thoth-Khonsu, the ibis-headed moon god who was worshipped as the god of wisdom and credited with devising hieroglyphics. Thoth also functioned as scribe to the gods and played a major part in Afterlife rituals. “At the Temple of Khonsu in Thebes, statues of Khonsu in the form of a baboon fronted the complex. In the Late Period, we know from a baboon tomb at Saqqara that the god Thoth-Khonsu became an important nocturnal oracle god, to whom written petitions were submitted. In this form, during the Greek Period, he was called Metasythmis, meaning “"hearing ear”,” reveals Jimmy Dunn.
Quartzite sculpture of a seated hamadryas baboon (c. 1400 BC), depicting the god Thoth. British Museum. (Photo: CC by SA 3.0 / Steven G. Johnson )
Astennu, the attendant of Thoth, was represented as a hamadryas in his capacity as recorder of the outcome of the crucial Weighing of the Heart ceremony; and as one of the four hamadryas baboons guarding the Lake of Fire in Duat or the underworld. “The image of the Thoth baboon beside a wedjat eye occurs on magic wands as early as the twentieth century BC. Two baboon forms of the god Khons controlled The Books of the End of the Year. These contained lists of those who were destined to die and those who would live,” explains Egyptologist, Dr Geraldine Pinch.
Scribe Nebmerutef is portrayed under the attentive gaze of the god Thoth, patron of writing. He is engrossed in reading a document, seated cross-legged on the ground, with his torso leaning slightly forward, and his right hand resting on the papyrus. Above him, the baboon sacred to Thoth is seated on a pedestal. Louvre Museum, Paris.
During the ceremony to renew the physical world and the person of the ruler, individual ancestors were ritually deified in the form of baboons and received cultic offerings. The erection of wooden kiosks containing ancestor baboons at the Heb Sed-festival of royal rejuvenation may have developed from this earlier practice. An image of a baboon representing King Narmer, erected by an official, implicitly suggests the transformation of the king into a baboon, as part of a rejuvenation festival. It is interesting to note that the king was identified with a baboon god known as the “Great White One”. Some scholars opine that the title of this god is derived from the silver-gray mane of a dominant hamadryas.
Limestone relief panel showing two baboons offering the wedjat eye to the sun god Khepri, who holds the Underworld sign. Late Period–Ptolemaic Period. Metropolitan Museum of Art , New York.
Essence of Divine Association
The most important aspect of baboons, however, was their association with Ra, the mighty sun god. In keeping with this, we find numerous depictions of these animals adoring the sun with raised arms, or holding a solar symbol. The baboon, in his aspect as Hapy, one of the four sons of the falcon-headed god Horus, was represented on canopic jar stoppers as he was in charge of protecting the lungs of the deceased. Hapy was also depicted in funerary literature as protecting the throne of Osiris in the Underworld.
This large quartzite statue of Thoth as a baboon was erected by Pharaoh Amenhotep III. Hermopolis/El Ashmunein. (Photo: Tatiana Matveeva / flickr )
From the New Kingdom onward, temple statues of baboons are more in abundance. They frequently appear to be squatting on a raised platform, often accessed by a flight of stairs. Giant quartzite baboon sculptures from the reign of Amenhotep III have been found in Hermopolis, Middle Egypt. The age of votive mummies began during the Twenty-sixth Dynasty (Ca. 664 BC) and by the Late and Graeco-Roman Periods (332 BC -395 AD) we find buried in the necropolises various primates including hamadryas, baboons (Papio cynocephalus anubis), green monkeys (Cercopithecus aethiops), red monkeys (Cercopithecus pata), and the barbary ape (Macaca sylvanus).
[The author thanks Merja Attia and Margaret Patterson for granting permission to use their photographs in this series. The public archives of the Metropolitan Museum of Art can be accessed here.]
[Read Part 2 ]
ROLE OF VIRUSES IN HUMAN EVOLUTION
YEARBOOK OF PHYSICAL ANTHROPOLOGY 46:14 – 46 (2003)
© 2003 WILEY-LISS, INC.
Linda M. Van Blerkom
Department of Anthropology, Drew University, Madison, New Jersey 07940
KEY WORDS infectious disease hominids paleoepidemiology
The study of viral molecular genetics has produced a considerable body of research into the sequences and phylogenetic relationships of human and animal viruses. A review of this literature suggests that humans have been afﬂicted by viruses throughout their evolutionary history, although the number and types have
changed. Some viruses show evidence of long-standing intimate relationship and cospeciation with hominids, while others are more recently acquired from other species, including African monkeys and apes while our line was evolving in
that continent, and domesticated animals and rodents since the Neolithic. Viral selection for speciﬁc resistance polymorphisms is unlikely, but in conjunction with other parasites, viruses have probably contributed to selection pressure
maintaining major histocompatibility complex (MHC) diversity and a strong immune response. They may also have played a role in the loss in our lineage of N-glycolylneuraminic acid (Neu5Gc), a cell-surface receptor for many infectious agents. Shared viruses could have affected hominid species diversity both by promoting divergence and by weeding out less resistant host populations, while viruses carried by humans and other animals migrating out of Africa may have contributed to declines in other populations. Endogenous retroviral insertions since the divergence between humans and chimpanzees were capable of directly affecting hominid evolution through changes in gene expression and development. Yrbk Phys Anthropol
46:14 – 46, 2003. © 2003 Wiley-Liss, In
Acute life strategy: A strategy (similar to r-selection) in which a virus increases ﬁtness by increasing its reproductive rate (offspring produced per parent
generation). Often disease-associated, it is characteristic of viruses with high mutation rates and the ability to infect multiple host species. Viral transmission tends to be horizontal and is more dependent on host population structure and density than it is for viruses using a persistent life strategy (Villarreal et al., 2000).
Apparent competition: The process by which the sharing of a common enemy (a predator or pathogen) can lead to consequences similar to those of more conventional forms of interspecies competition for limiting resources (Holt and Lawton, 1994).
Coevolution: Reciprocal evolutionary change in interacting species (e.g., host/parasite, predator/prey, plant/herbivore, or mutualism), with changes in the
two species caused by mutual selective pressure.
Cospeciation: Parallel speciation of two organisms with a close ecological association (e.g., host and parasite), such that cladograms of the two are congruent.
Endogenous retroviruses: DNA sequences, related to those of infectious retroviruses, that are integrated into host genomes and have lost the ability to cause active infection thought to be remnants of ancient germ-cell infections, they have proliferated and evolved by retrotransposition.
Error-catastrophe threshold: The level of criticalcopying ﬁdelity below which (i.e., the base substitution rate above which) viral genetic information can
no longer be maintained and nucleotide sequences
would become essentially random (Domingo and Holland, 1994).
Gene capture: De novo gene acquisition via recombination of a viral genome with that of the host or another virus.
Host-linked evolution: A form of cospeciation, in which well-adapted viruses living in single hosts, through ancient association with them, have diverged and speciated along with their hosts. Isolation of virus populations and selection pressure exerted by the host are important factors in this process, which results in a correlation between virus and host phylogenies (Chan et al., 1997).
Hyperdisease: An extremely lethal disease introduced into a region by a carrier species that is relatively unaffected by it at the same time, it is capable
of infecting a variety of other species with high mortality rates and has the potential for causing their extinction (MacPhee and Marx, 1997).
Modular evolution: Acquisition of new active genes by recombination of speciﬁc nucleic acid sequences or functional domains within genes common in viral
evolution, with recombination occurring both between and within viral taxa.
Parasite-mediated competition: A form of apparent competition, by which the sharing of a pathogen by two species can result in population decline, even extinction, of one of the hosts, even in the absence of resource competition (Holt and Pickering, 1985).
Persistent life strategy: A strategy in which a virus increases ﬁtness by increasing the survival time of its offspring, thus enhancing persistence in an individual host and the probability of transmission over time. Characteristic of genetically stable viruses that show cospeciation with their hosts, this strategy is often associated with vertical or sexual transmission. Latent infection, with the capacity of the
virus to reactivate, is a frequent result (Villarreal et al., 2000).
Quasispecies: A virus population of closely related but distinct genetic variants resulting from an errorprone replication process (typical of RNA viruses, in
particular) a self-sustaining population of sequences that reproduce themselves imperfectly but well enough to retain a collective identity over time, but which also contain the potential to produce more virulent strains (Eigen, 1993).
Zoonosis: An infection or infectious disease transmissible under natural conditions from other vertebrate animals to humans most zoonoses are deadend infections with little or no transmission among human hosts.
The study of human evolution has concentrated on humans and their hominid 1 ancestors, without as much attention to other organisms also evolving in the same environments. But a population must constantly interact with and adapt to these other organisms if it is to survive and reproduce. Food species, predators, and agents of infectious disease have all played a role in human evolution, and among the latter, viruses were probably particularly important.
As signiﬁcant causes of morbidity and mortality, and in their capacity to act as “molecular genetic parasites” (Luria, 1959), viruses are in a strong position
to inﬂuence the evolution of their hosts (May, 1995 Villarreal, 1999 Balter, 2000). While this is wellrecognized in studies of the evolution of other organism (especially plants, e.g., Thompson and Burdon, 1992 Simms, 1996), the impact of infectious disease on human evolution has not received the attention it deserves (Swedlund, 2000). Yet viral parasites have probably played an important role in human evolution (de Souza Leal and Zanotto, 2000). The purpose of this paper is to review recent work in the molecular genetics of human viruses and to assess the extent to which viruses were signiﬁcant parasites of earlier hominids (and thus in a position to have affected human evolution before the Neolithic). It also speculates on the roles they may have played.
Haldane (1949) was among the ﬁrst to suggest that the struggle against infectious disease was an important evolutionary process, and he described some possible effects. A disease that kills or lowers fertility is a likely selective agent. It can be an advantage or a disadvantage to a species in competition with others, even contributing to extinction.
Most species contain considerable genetic diversity in their resistance against disease, and considering the speed with which new pathogens evolve (in general much faster than the host), it is in the best interests of the host to be genetically diverse and highly mutable in the loci concerned with disease resistance. In the view of Haldane (1949), disease may even favor speciation, by coupling this diversity
and mutability with geographic isolation. In addition, transmission requirements may have contributed to host population size and structure and behavioral characteristics such as negative reaction to fecal odors.
As the scientiﬁc community became more aware of “surprising biochemical diversity” (Haldane, 1949, p. 329) in virtually every animal investigated, geneticists sought to explain it. Estimates of the proportion of polymorphic loci ranged from 20 – 40% in
vertebrates and about 30% in humans (Selander et al., 1970). Some suggested that interactions between parasites and hosts played an important role in maintaining this degree of polymorphism (Clarke, 1976). Hamilton et al. (1990) suggested that the
need for genetic diversity in a “host-pathogen arms race” even contributed to the evolution of sexual reproduction. We now know that this level of polymorphism (30%) is probably an underestimate, based on incomplete sampling of rare mutations.
Given the frequency of DNA polymorphism (about one in every 500 nucleotides), nearly all genes may be polymorphic (Cavalli-Sforza et al., 1994). The human genome is now estimated to contain between two and three million single-nucleotide polymorphisms (SNPs), and even though less than 1% are estimated to result in variation in proteins, this still leaves enough to involve many more than 30% of the estimated 20,000 ,000 human genes (International Human Genome Sequencing Consortium, 2003 Venter et al., 2003).
Disease-driven selective pressure is now considered a likely reason for the astonishing degree of polymorphism in the major histocompatibility complex (MHC), which codes for membrane glycoproteins [also known as human leukocyte antigens
(HLA) in humans] that play an important role in the immune system by binding fragments of infectious origin and presenting them to T-cells (Zinkernagel et al., 1985 Howard, 1991). The importance of maintaining this ﬁrst line of defense against invading pathogens is emphasized by the discovery that some polymorphic alleles in the MHC system predate the divergence between chimpanzees and humans, and have been transmitted through speciation bottlenecks via “trans-species selection” (Takahata, 1990).
This paper uses traditional taxonomic nomenclature, by which the term “hominid” refers to humans and their bipedal relatives, while apes and humans are included in the hominoids.
ROLE OF VIRUSES IN HUMAN EVOLUTION 15 TABLE 1. Animal virus families
Family Description Evolution
Adenoviridae Medium-sized DNA viruses that cause respiratory and enteric
infections in birds and mammals numerous subtypes in humans and other primates.
Evolved along with warm-blooded animals subtypes diverged during evolution of
primates (Song et al., 1996).
Arenaviridae RNA viruses, mostly zoonotic and maintained in rodent reservoirs spread via contact with infected rodent secretions, e.g., Lassa fever and lymphocytic
choriomeningitis viruses. Long-term coevolution with rodent hosts hominids unlikely to have encountered them before agriculture and permanent houses (Bowen et al., 1997).
Astroviridae RNA viruses with worldwide distribution in humans and other animals water- and food-borne signiﬁcant cause of diarrheal disease in developing countries.
Not much known about these yet.
Bunyaviridae Among larger RNA viruses, these are zoonotic and emerging mostly arthropod-borne (e.g., Rift Valley fever, California encephalitis, Crimean-Congo hemorrhagic fever), except for hantavirus. Originated in insects and coevolved with
them hantavirus phylogeny shows coevolution with rodents and hostswitching (Zhao and Hay, 1997 Vapalahti et al., 1999).
Caliciviridae RNA viruses with worldwide distribution in humans and other vertebrates common cause of diarrhea in children transmitted via contaminated food and water or uncooked shellﬁsh. Sequences show geographic similarities that transcend host relationships readily move across species barriers passed back and forth between humans and domesticated animals (van der Poel et al., 2000).
Coronaviridae Largest RNA viruses, infecting humans, cattle, pigs, rodents, cats, dogs, and chickens common cause of colds in humans and a variety of conditions in other animals, primarily enteric and respiratory CV-like particles found in stools of adult chimps, macaques, baboons, and marmosets. Antigenic drift and recombination
constantly produce new strains interspecies spread leads to episodic evolution (Lai, 1995).
Filoviridae RNA viruses that infect only vertebrates contains two species(Ebola and Marburg) that cause acute fatal disease in humans and other primates reservoirs unknown. Two species estimated to have diverged 7 kya, and Ebola subtypes diversiﬁed 1 kya (Suzuki and Gojobori, 1997).
Flaviviridae RNA viruses, including numerous arboviruses (e.g., yellow fever, dengue, West Nile, tick-borne encephalitis), bovine diarrhea, hog cholera, and hepatitis C-like viruses (HCV, GBV-A, -B, and -C) GB-viruses widely distributed in simians.
Mosquito-borne viruses originated in Africa, have affected primates for a long time. HCV long-term presence in Africa as well, but infects only humans GBviruses show cospeciation with primates GBV-C had ancient association with humans (Gaunt et al., 2001 Robertson, 2001).
Hepadnaviridae Hepatitis B viruses found in primates, New World rodents, and birds among smallest viruses contain partially doublestranded circular DNA replicated via RNA intermediate and reverse transcriptase. May have cospeciated with primates
human strains result of ancient interspecies transmission in Africa now
found in isolated human populations in both hemispheres (Simmonds, 2001).
Herpesviridae Large DNA viruses most vertebrate species have at least one.
Three subfamilies alpha- (herpes simplex, varicella), beta-(cytomegalovirus), and gammaherpesvirinae (Epstein-Barr, Kaposi’s sarcoma). All contain many strains found in other animals, including primates.
Ancient divergence of subfamilies with tissue speciﬁcity acquired early, at least 200 mya have since coevolved in close association with hosts (McGeoch et al., 2000 McGeoch, 2001).
Orthomyxoviridae Inﬂuenza subtypes A, B, and C RNA viruses with segmented genomes that readily reassort, producing pandemic inﬂuenza A wild A strains, maintained in avian hosts, also infect pigs, horses, and other mammals subtypes B and C infect humans only. Subtype A appears to be ancient parasite of aquatic birds avian virus strains are in “evolutionary stasis” recent and explosive evolution in pigs and humans (Webster, 1997).
Papovaviridae Widespread and numerous viruses with very small circular DNA include papillomaviruses that cause cutaneous or genital lesions (e.g., warts, genital papilloma) and polyomaviruses (JC and BK viruses, simian virus-40) that infect kidney cells highly species-speciﬁc all mammal, bird, and reptile species so far studied carry species-speciﬁc PVs, with most infected by several types HPV and JC found in nearly all human populations.
Papilloma species and type diversity suggests a well-adapted parasite intimately associated with hosts for a long time and cospeciating with them also coevolved with humans can be used to trace migrations (Ong et al., 1993 Van Ranst et al., 1995). JC is ubiquitous human pathogen whose genotypes diverged when human populations did(Hatwell and Sharp, 2000).
Paramyxoviridae RNA viruses that include parainﬂuenza, mumps, morbilliviruses (e.g., measles, distemper, rinderpest), and many other viruses of humans and other animals include emerging viruses Nipah and Hendra transmission primarily by airborne droplet. Animal morbillivirus phylogeny matches that of host species, but human viruses probably resulted from recent interspecies transmission from domesticated animals (Norrby et al., 1992). 16 L.M. VAN BLERKOM
While such positive selection is still believed to have maintained many MHC allelic lineages, the sharing of MHC polymorphisms by different mammalian orders and even some within the primates (e.g., between humans and New World monkeys) may be the
result of convergent evolution (Yeager and Hughes, 1999 Kriener et al., 2000).
Zoologists now recognize that infectious diseases may mediate “apparent competition” between species and augment the danger of extinction (Hudson and Greenman, 1998 Daszak et al., 2000).
Some have even suggested a “hyperdisease” scenario, involving infections carried by migrating humans or their dogs, to explain Pleistocene megafaunal extinctions (MacPhee and Marx, 1997).
Yet another way in which pathogens can affect the evolution of their hosts is through direct interaction with host DNA. By virtue of their simplicity and
their need to use host-cell replication and transcription machinery, viruses act as “molecular genetic parasites” (Luria, 1959) and may alter host genomes through such mechanisms as recombination, retrotransposition, and gene conversion. While lasting
effects are more frequent in unicellular hosts and plants, ancient germ-cell infections by retroviruses have left their mark on human and other primate genomes (Sverdlov, 2000).
TABLE 1. (Continued)
Family Description Evolution
Parvoviridae Among smallest, simplest viruses known, with single-stranded
DNA genomes widespread in many vertebrate and invertebrate hosts tend to infect rapidly dividing tissues(mostly fetal, intestinal epithelial, and bone marrow).
Very species-speciﬁc viral evolution tightly linked to that of host (Shadan and Villarreal, 1993), but not much known about human parvoviruses.
Picornaviridae Several genera of RNA viruses: Aphthovirus (foot-and-mouth disease), Cardiovirus (encephalomyocarditis), Enterovirus(Coxsackie, echo, polio), Hepatovirus (hepatitis A),Parechovirus, and Rhinovirus (colds) last four genera infect
mainly humans, with domesticated animal viruses probably derived from human strains.
Diverse and numerous simian viruses are all from Old World primates and are closest known relatives of human enteroviruses some picornaviruses may have been long associated with humans (Gromeier et al., 1999).
Poxviridae DNA genome largest and most complex viruses known vertebrate subfamily includes large number of poxviruses infecting many animals (e.g., variola, vaccinia, cowpox, monkeypox, camelpox, fowlpox, sheep-and-goatpox, swinepox) plus molluscum contagiosum virus of humans. Many (e.g., cowpox, monkeypox) are maintained in rodent
Origins of variola (smallpox) unclear may be ancient hominid virus (like molluscum contagiosum) that recently became more virulent, or may be more recently evolved from African rodent virus (Fenner et al., 1988 Tucker, 2001).
Reoviridae “Respiratory enteric orphan” viruses, with double-stranded RNA genomes ubiquitous in nature, implying wide cell tropism, ubiquitous receptor infect vertebrates (mammals, birds, reptiles, ﬁsh), invertebrates (insects, molluscs), and
plants found in all mammals except whales human varieties include rotaviruses, common cause of severe diarrhea worldwide major cause of mortality in young of
many species include many emerging viruses that cause hemorrhagic fever, encephalitis, Colorado tick fever. Rapid evolvers members of various genera among most evolutionarily divergent RNA viruses (Duncan, 1999) frequent interspecies transmission and reassortment of segmented genome give different trees for different genes and close relationship between human and nonhuman rotaviruses (Cunliffe et al.,
Retroviridae RNA viruses that reproduce using reverse transcriptase and a DNA intermediate subgroups include lentiviruses (e.g., HIV, SIV) primate T-cell lymphotropic viruses (PTLV) endogenous retroviruses (ERV) in wide variety of
vertebrates, and can jump host species, sometimes across wide phylogenetic distances
Great antiquity retroviruses and retroid elements found in all eukaryotes
infectious retroviruses found only in vertebrates and may have evolved from
retrotransposons extremely fast mutation rates, but can also be very
stable (e.g., as integrated provirus) some SIVs show evidence of cospeciation
with hosts, while others are result of recent interspecies transmission (HIV-1
from SIVcpz and HIV-2 from SIVsm) HTLV-I and -II likewise from STLVs of Asian macaques and bonobos, respectively (Holmes, 2001 Salemi et al., 2000).
Rhabdoviridae RNA viruses that include genus Lyssavirus (rabies) and vesicular stomatitis virus there are no speciﬁcally human rhabdoviruses, but rabies is one of most dangerous zoonoses. Very ancient family contains members that infect animals and others that infect plants rabies appears derived from lyssaviruses of African bats(Amengual et al., 1997).
Togaviridae RNA viruses, mostly mosquito-borne and in genus Alphavirus, including a number of zoonotic viruses maintained in rodent and bird reservoirs (e.g., Eastern and Western equine encephalitis, Semliki Forest virus) also genus Rubivirus
(rubella), which is not vector-borne and infects only humans. Evolved in insects contain segments from plant viruses via recombination in insect
hosts (Lai, 1995). Origin of rubella not known.
Before one can judge the likelihood of any of these processes contributing to human evolution, one must determine whether our hominid ancestors suffered signiﬁcantly from infections, whether they could have been signiﬁcant causes of morbidity or
mortality (and thus agents of selection), and what kinds of parasites may have been involved.
The study of human disease history has tended to assume an epidemic disease model and a focus on human ecology and population history, with most infectious diseases considered to have evolved since the increased size and concentration of human populations in the Neolithic (Cockburn, 1967b Burnet and White, 1972 Armelagos and Dewey, 1978). The impact of parasitism before that time was not considered very important, as it appeared to be restricted to chronic latent infections unlikely to cause serious disease and the occasional zoonosis (disease of another animal species). Meanwhile, the inﬂuence of disease on human affairs since the Neolithic was
acknowledged to have been considerable (McNeill, 1976). Humans were assumed to have had few viral diseases before the Neolithic (Burnet and White, 1972), but studies of antibodies in isolated South American tribes suggested that small isolated groups had their share of infections (Neel et al., 1964, 1968 Black, 1975), and Cockburn (1967a) recognized the presence of many viruses in wild primates and thus, probably, in our ancestors. Perhaps infectious agents, and viruses in particular, were
more important than we thought.
Recent advances in molecular virology have provided a gold mine of information about the evolutionary history of the most important human viruses, and this allows one to decipher when they might have entered our line (Zimmer, 2001). Deep phylogenetic branches, high genetic diversity, global distributions, and trees showing cospeciation with primate hosts all suggest ancient association of many viruses with humans, while close relationships with viruses infecting other species (especially
rodents and domesticates) suggest more recent acquisition of others. The ease with which our species acquires emerging infections from other primates points to the importance of these zoonoses as a source of human disease, both now and in the past.
When mapping the evolutionary relationships of human and animal viruses, one obtains a different picture depending on whether the viruses in question are DNA-based, RNA-based, or replicated using reverse transcriptase, so these types are discussed