Disease as a
Factor in the Neandertal's Demise
by: Jaimi N. Butler
University
of California, Santa Barbara
© Jaimi N. Butler, 2003,
All
Rights Reserved
TABLE
OF CONTENTS
A brief
introduction to Neandertals
Possible
Diseases
Diseases
crossing the species barrier
The
impact of disease on virgin populations
Skeletal
evidence
Adaptations
against disease
Conclusion
ABSTRACT
The
Neandertals were hominids that had become firmly established within
their
European territory. However, within
just several thousand years, they seem to disappear from the
archaeological
record. This disappearance coincides
with the arrival of anatomically modern humans coming out of Africa. Theories abound in explanation of this
occurrence. Yet, in addition to these
eminent theories, other alternate or complementary explanations exist
to
explain the demise of the Neandertals.
This article outlines the transfer of infectious disease from
the early modern
humans to the Neandertals as a feasible contributor to their extinction.
The Neandertals are
one of the most
well-known early hominids. Regardless
of whether one accepts the Neandertal as a possible distant ancestor or
merely
a dead end, they continue to be an enigma tangled somewhere in the
branches of
human evolution. Controversy clings to
every facet of the Neandertals, and still today, questions abound
concerning
them: had they acquired language?, what type of cognitive abilities did
they
posses?, did they have culture?, were they replaced by incoming early
humans or
did they interbreed with them and ultimately contribute to our gene
pool? The science of paleoanthropology is
advancing and answers to these questions may soon come.
However, one question involving the
relationship between Neandertals and early modern humans has yet to be
discussed: Was disease brought from Africa by early modern humans and
if so,
was it a factor in the demise of the Neandertals? This
is a question that we may find an empirical answer for
somewhere in the near future. Despite
the fact that it is a highly feasible probability, this question has
not been
addressed within anthropological literature.
In the following argument I will draft detailed explanations to
support
the hypothesis that the role of incoming disease may have had a
destructive
impact on the Neandertal population.
Various factors contribute to this
hypothesis. Ideally skeletal remains would
tell the
story of disease and its effect; however, when analyzing for disease,
the
information derived from the actual bones is slim.
Yet alternative evidence does provide a strong case for the
possibility of disease playing a role in the decline of the Neandertals. I will examine the variety and lethality of
possible diseases, diseases that cross the species barrier, the
devastating
impact of disease on New World inhabitants when Europeans invaded as a
comparative case, the available pathological skeletal evidence, and the
varied
adaptations against disease. This
evidence will provide a supplemental hypothesis to what is already
understood
concerning the Neandertal's collapse.
A brief
introduction to Neandertals
Although the human evolutionary tree is
periodically revised, paleoanthropologists now know that Neandertal
ancestors
were from one of the first waves of hominids that came out of Africa
about 1.8
to 2 million years ago. This early
hominid, classified as Homo ergaster,
would eventually evolve into H. neanderthalensis
in parts of Europe and the Middle East, H.
erectus in Eurasia, and eventually H. sapiens
in Africa.
It is believed that Neandertals were
indigenous to
Europe (Klein 1999: 394). Fossil
evidence suggests Europe was inhabited roughly 600,000 years ago. This coincides with the proposed split
between Neandertals and modern humans suggested by mtDNA evidence
(Klein 1999:
393). However, mtDNA analysis has yet
to be proven completely accurate and new discoveries might contradict
its
evidence. Nonetheless, a multitude of
archaeological evidence, coming from well-studied sites, supports the
idea that
Neandertals were occupying parts of Europe at least half a million
years ago
with (Klein 1999: 393). This indicates
that the Neandertals had a long history in Europe and ultimately parts
of the
Middle East and western Asia.
In addition to confirming the
Neandertal's
occupation of Europe and parts of the east, skeletal morphology also
supports a
long period of residence in those areas.
Adaptations for that particular environment, specifically to
climates of
continuing glaciation, include robusticity and shorter stature that,
according
to Bergmann and Allen's rules, better conserve heat (Klein 1999: 389). The Neandertal's short limbs and larger
torso are indicative of adaptations for cold climates (Klein 1999: 389). Moreover, the Neandertals had a large nasal
aperture that may have allowed for the cold air to be warmed prior to
entering
the body in order to conserve heat (Klein 1999: 392).
What the aforementioned evidence implies
is that the
Neandertals had been thriving in their homeland for a long period of
time – so
long that they had actually evolved adaptations to better live in their
environment. With such a strong hold in
their native land, how was it that within just several thousand years
the
Neandertals disappeared? It is known
that their disappearance corresponds with the migration of modern
humans into
the area (Klein 1999: 374). It has also
been determined through the fossil record that these populations may
have lived
in close proximity to each other, in some areas, for close to 7000
years (Klein
1999: 374). So, what actually happened
to the Neandertals? This is a question
that is still hotly debated today and opposing sides each have built up
strong
evidence in support of their claim.
Some paleoanthropologists believe that the Neandertals were
forced out
by the incoming moderns who were more technologically advanced and that
they
died out due to their inferiority (Wong 2000: 107).
Alternatively, some suggest that the Neandertals, once forced
out
of their own territory, were unable to reestablish themselves elsewhere
and
hence became extinct. Others claim that
warfare ensued with the anatomically modern humans being the victors. Additional allegations imply that moderns and
Neandertals cohabitated for several millennia and ultimately interbred. In fact the skeletal finds at Lagar Velho 1
researched by Erik Trinkaus may indicate a combination of Neandertal
and modern
human characteristics truly supporting the occurrence of inbreeding
(Trinkaus
and Duarte (2000) 102-103). This would
argue that the Neandertals as an entity became extinct yet their genes
remain
among us today (Wong 2000: 99-107; Smith 2000: 105).
Each contention has strongly argued and
valid
points. Moreover, each is reasonable
and they may all contain accuracies.
However, other admissible explanations do exist such as the
possibility
that disease may have played a role in the demise of the Neandertals. Disease need not have been the ultimate
culprit in the Neandertal's extinction rather it may have been one of
the many
factors that ultimately lead to their vanishing.
Possible
Diseases
We are all familiar with the infectious
diseases that afflict humans today, including AIDS and Tuberculosis,
and the
diseases that have impacted history, for example, the Bubonic Plague,
Influenza, and Cholera. But what many
do not know is how and why these diseases operate, more specifically
the
conditions that facilitate their spread.
The diseases that are now or were recently common typically
occur in
areas of dense population. It is this
environment that perpetuates the disease by providing it with countless
hosts
and victims. Jared Diamond refers to
these as "crowd diseases" (1999: 203) and explains that this genre of
disease would not be successful (speaking from the pathogen's
perspective) in
small bands of hunters and gatherers.
This does not imply that these individuals were free of disease,
rather
it proposes that other kinds of diseases would have existed. Some key differences between modern
agricultural populations and hunter-gatherers are that they live in
small
numbers, collect food on a basis of need rather than quantity, and tend
to be
nomadic. This provides them with the
advantage of not stockpiling food, thereby preventing the presence of
rodents
(who are known to carry disease). Also,
their nomadic lifestyle would keep them from cohabitating with large
amounts of
rubbish and/or their own waste, which again is beneficial in averting
pathogens. Finally, their small
population numbers are unwelcoming to invasion by the crowd diseases. Nevertheless, other diseases also plague
this type of group and they are most likely "…the oldest diseases of
humanity." (Diamond 1999: 204).
Several diseases exist that, due to
their specific characteristics, can be sustained in smaller populations. Among these diseases are the diseases caused
by Treponema pallidum, Tuberculosis,
and Varicella Zoster (Chicken pox and
shingles). These diseases each have
long periods of latency and/or dormancy where "…the victim remains
alive
as a reservoir of microbes to infect other members of the tribelet."
(Diamond 1999: 204).
Treponema pallidum
The T.
pallidum bacteria are expressed in a series of diseases: venereal
syphilis,
non-venereal syphilis (also known as bejel), yaws, and pinta. Each of these shares many common
symptoms. They each exhibit several
stages following the initial infection.
With the first stage a lesion will most likely appear that can
persist
for weeks to months and then disappear.
At onset of the second stage more lesions appear in greater
quantity
than in the first stage. It can take
many years after the original lesions for these secondary crops to
erupt. It is because of these prolific
lesions that
transmission of this bacteria can take such a simple route. If a third
stage
exists in a particular case it can take up to 40 years to surface. By this time the disease has taken its toll
on the body affecting the brain and nervous system, bones, joints,
cartilage, and/or
the skin (Antal et al. 2002: 83, 86-88).
For example, both yaws and syphilis can produce tumors that go
through
the skin and begin to attack the bone tissue leaving defining evidence
of the
lesion (Wills 1996: 189). Extant
victims of T. pallidum are typically
easy to recognize due to these well-defined
pathologies, however, most skeletal remains only leave subtle clues.
These diseases are all forms of the T. pallidum bacteria and each have
evolved into these different types in order to maximize or sustain
their
transmission within varied climates and environments.
"…[T]his fragile web of adaptations implies that Treponema
has had a long history of
association with humans" (Wills 1996: 200). It
is suspected that yaws was the incipient form and that it
originated alongside our early ancestors in tropical regions of
sub-Saharan
Africa (Wills 1996: 203). Even today,
yaws "…is the most prevalent endemic treponematosis effecting the rural
populations in the rain forest areas of the world where high levels of
humidity
and rainfall prevail" (Antal et al. 2002: 86). Bejel,
the non-venereal form of syphilis, seems to be an evolved
form of yaws. Bejel is better adapted
to more temperate or hot and dry climates, such as the Middle East and
northern
Africa (Antal et al. 2002: 87).
However, it has previously been endemic in northern Europe,
Russia, the
Balkans, Mongolia, the Near East, and southern Africa (Antal et al.
2002:
87). Venereal syphilis seems to have
evolved in colder areas where people would normally be more fully
clothed. Therefore, the mode of
transmission would
have shifted from external to internal means via sexual transmission.
This bacteria's adaptability to various
types of
climates gives it strong standing among possible diseases leading to
the
Neandertal's demise. A disease with
this ability could have survived the many different climatic regions
that the
early moderns would have passed through when leaving Africa. With this as evidence, the claim can be made
that the early ancestors coming out of Africa could have been carrying
either
of these diseases or one of their predecessors. Besides
their endemic regions, yaws and bejel have quite a bit in
common. They are both prevalent in
rural areas where people are scantily clad and are transmitted when
secretions
from a lesion are introduced to another person via an opening in the
skin
and/or mucous membrane. These modes of
transmission could have been supported during the invasion of
Neandertal land
by early humans if there was sexual or casual contact among the groups,
physical conflict, transfer among children during play, or in more
civil
dealings such as trading. In addition,
even isolated instances of contact between Neandertals and the infected
early
modern humans could have initiated the spread of the disease to the
Neandertal
population. After that initial
transmission the disease would easily have spread among even those
without
direct exposure to the early modern humans due to the lifestyles of the
tribe:
sharing food, drinking from the same vessel, huddling in groups to stay
warm,
caring for the young or elderly, and sexual contact.
It would not have taken intense contact between the two factions
for the disease to become endemic within the Neandertal population.
These treponemal diseases do not always
result in
death, yet the debilitating consequences on bones and joints would have
had
disastrous outcomes. Some infected
individuals would have become partially handicapped and would not have
been
able to provide for themselves or contribute to the group.
Others might have been considered unsuitable
as mates and/or ostracized due to their appearance.
This type of effect could have led to them to being banished or
neglected by the remaining group members.
In addition, venereal syphilis can be passed from mother to
fetus, which
results in still births approximately half of the time (Wills 1996:
190). If a syphilis-like disease had been
introduced to the Neandertals, it could have drastically lowered their
birth
rates. Decreased birth rates along with
the other negative factors stemming from T.
pallidum infection could have had a serious impact on the
Neandertal's
population.
Tuberculosis
Because of its latency period and mode
of transmission Tuberculosis also presents itself as a possible disease
that
could have affected the Neandertals.
The human oriented type of Tuberculosis is known as a bacterial
respiratory disease. However, it can
spread from that region and affect other parts of the body including
other
organs and long bones (Filer 1996: 69).
Tuberculosis is spread when an infected individual expels
bacteria-laden
droplets by coughing, talking, or sneezing that can then be inhaled by
any
person within close proximity. The
bacteria travels to the lungs where it will multiply causing slight
inflammation at the site. At this point
the area of the lung will either heal, while perhaps encapsulating a
portion of
the bacteria, or will fail to heal and the infection will persist. However, both situations leave the
individual at risk. In the first
instance, where the area has healed, the scarring can eventually break
down and
release the pathogen back into the lungs.
Once the bacteria population has increased the lung reacts by
flooding
the area with cells and fluids. This
defense by the lung, although meant to evacuate the irritant, destroys
the
tissue – colloquially referred to as consumption (Burnet 1953: 291-303;
Burnet
and White 1972: 213-224). If this
occurs on a grand scale, large portions of the lung will become damaged
and the
person will have less surface area in which to oxygenate their blood
–ultimately leading to death. By using
modern day statistics I can provide a better illustration of the threat
of
Tuberculosis. Roughly 10 percent of
those infected with the Tuberculosis bacterium will develop the disease
over
their lifetime and in 1 percent of them it will become lethal (Garret
1994:
513). As will be discussed later,
diseases typically have a more profound impact on groups of people who
have
been isolated from the pathogen.
Therefore, these statistics should not take away from the
possible
detriment of Tuberculosis on the virgin Neandertal population. Figures from 1988 indicate that in that year
about 2 billion people were infected with the bacteria (Garrett 1994:
513). Although this number does not
translate well when considering populations of early hominids who lived
half a
million years ago – it does indicate how rampant the microbe can be
within a
population. Most interesting about the
Tuberculosis bacteria is how our immune system can keep it at bay for
long
periods of time. However, during
periods of stress and compromised immune systems the bacteria can
reappear and
wreak havoc on a population.
Because of this anomaly, I speculate
that had the early modern humans, coming out of Africa, been previously
exposed
to the bacteria that they could have easily sequestered the microbe
within
their lung tissue. Once they arrived
into parts of Europe they would have found themselves in climates they
were not
used to and then faced with a new people.
These early humans would have been thrust into extremely
stressful
situations which may have been the catalyst needed to release the
bacteria back
into their lungs. Once this occurred,
they could have freely transmitted the disease to the Neandertals. Although, the reintroduction of the disease
to the early moderns may have resulted in some of their deaths it could
have
proven to be extremely disastrous for the Neandertals since this would
have
been a novel disease for them.
Tuberculosis is highly effective in its
transmission, only needing the infected individual to cough or sneeze
for it to
be swept out into the open air and drawn in by another person. This would have made Tuberculosis highly
contagious in the living conditions of the Neandertals.
With families dwelling in caves and confined
shelters, the disease would have spread rapidly.
Varicella Zoster
Varicella
Zoster is a disease that presents itself in two forms: Chicken pox
and
Shingles. This virus is also a
plausible candidate in this argument due to its period of latency and
its
methods of transmission. In its Chicken
pox form V. zoster is transmitted
through droplets expelled from an infected person when they cough or
sneeze. When expressed as Shingles the V. zoster virus can only be spread by
direct contact with the pustule. A
person infected with this disease will first have Chicken pox, then the
virus
will find its way to a nerve cell nucleus where it remains latent until
reactivation
to its Shingles state (Crawford 2000: 120).
Most interesting about V. zoster
is this period of latency and how it can reintroduce the virus to a
vulnerable
population every couple of decades.
Though the Shingles state of this disease is infectious, it only
spreads
the initial V. zoster virus that will
then cause Chicken pox. Once exposed to
V. zoster and the initial outbreak of
the chicken pox infection most people are immune to another Chicken pox
episode
yet, still susceptible to the reintroduction of the virus as Shingles.
Although Chicken pox and Shingles are
not commonly
fatal, this virus does pose a risk to newborns, infants, and pregnant
women
(Well-Connected 2001). In rare cases of
Chicken pox, the virus can cause inflammation or infection of the
brain, stroke,
and high fevers that sometimes result in death (Well-Connected 2001). In addition, people who contract the virus
for the first time as an adult are at a greater risk of complications,
even
death. Another consideration is that
these complications nowadays would be treated with immediate medical
attention
whereas in prehistoric times the person would have most likely
succumbed to the
illness.
V.
zoster's means of
transmission
would have been facilitated among the Neandertal population. Archaeological remains indicate that they
were living in caves and rock shelters.
In this type of setting and with families huddling to stay warm
transmission through droplets or direct contact with pustules would
have been a
frequent occurrence. Had V.
zoster been introduced by the
incoming early modern humans, all Neandertals would have been
susceptible to
this disease including infants and adults – the two groups that are
most prone
to complications. This disease would
have spread among the Neandertals until a number of them had been
exposed and
in due course become immune. But it
would only take a wave of new births coinciding with a reoccurrence of
Shingles
to start this cycle again. This series
of disease occurring regularly would have put a strain on their
population that
could have ultimately resulted in their numbers being so low that they
would
not be able to defend themselves against the early modern humans or to
confront
any other issue at hand.
These several diseases surely possess
the
characteristics needed to have established themselves among small
populations
of Neandertals and early modern humans.
Although these diseases, as we know them now, are not
particularly
fatal, it is possible that they have recently evolved this low level of
virulence. Diseases evolve varying
degrees of virulence depending on their environment, host
susceptibility, and
host availability (Ewald 1994: 36).
Regardless of their lethality these diseases would have produced
some
amount of negative impact on the Neandertals.
With those effects in combination with other environmental and
social
factors weighing upon them, the Neandertals could have easily become
extinct
within a relatively short period of time.
Diseases
crossing the species barrier
Diseases crossing the species barrier
are a regular occurrence. In fact, some
of the diseases already mentioned and many others have crossed the
species
barrier to humans from bovines, non-human primates, rodents, or birds
either
domesticated or wild. Examples of
diseases that have successfully done this are: Small Pox, Influenza,
Tuberculosis, most likely HIV, the Bubonic Plague, Ebola, and Anthrax. Therefore, for those who consider the
Neandertals to have been another species than the early moderns,
disease
remains a consideration. If pathogen
mutation can lead to the transmission of disease between a cow and a
human,
then one cannot debate the high likelihood that diseases could have
also spread
from invading moderns to the Neandertals.
The
impact of disease on virgin populations
We need not venture too far in history
to find the
effects of disease on virgin populations.
The disastrous ramifications of disease on the Amerindians is a
clear
indication of how detrimental a novel disease can be on a population. In William McNeill's Plagues and People
he writes that, although disease was not absent from the New World,
they
remained to some extent "biological[ly] vulnerable" (1998: 209). Skeletal analysis however, indicates death
was caused more by famine and crop failure (McNeill 1998: 210). Though their populations had grown to be
significantly large, it has been suggested that the limited number of
domesticated animals in the New World may have prevented the burgeoning
of many
diseases that were running rampant in the Old World (Mcneill 1998: 210). To further understand the consequence of
disease we can look at the population of Mexico that, prior to the
invasion by
the Spaniards, was estimated to have been roughly 25 to 30 million
people. These numbers dropped drastically
in only 50
years to less than 3 million people.
Although this decline in population included factors other than
disease,
such as battle casualties and most likely famine, the diseases
evidently played
an integral role in the Amerindians mass reduction (McNeill 1998:
211-213).
A more recent example of disease among
virgin
populations involves African natives working in Europe in the early
1900's. These individuals had little to
no previous contact with Tuberculosis until they became exposed while
working
and living in France's crowded conditions.
Due to their extreme vulnerability to this disease it seemed to
affect
them more profoundly then the European population.
These men had a much higher fatality rate than their French
colleagues and "…died of what was really an acute [tuberculous]
pneumonia." (Burnet and White 1972: 218-219).
These examples are provided to better
express the
devastating effects of novel diseases on susceptible populations whose
body
systems are unfamiliar with particular pathogens. They
should help in supporting the argument that disease remains
a plausible factor in the Neandertal's demise.
Skeletal
evidence
Skeletal evidence of disease is
generally very limited, as "…most of the great epidemics that have
punctuated human history will leave, at best, nonspecific and indirect
evidence
in a skeletal sample." (Verano et al. 1992: 5). As
with the Neandertal's, a majority of the pathological evidence
pertains to such chronic disorders as arthritis instead of infectious
disease.
However, evidence of skeletal pathology
that resembles the effects of yaws has been found in several remains. The post-cranial bones of a H.
erectus individual KNM-ER 1808, have
thickened layers of bone 7mm thick located on the legs and arms (Klein
1999:
355; Rothschild et al. 1995: 343). This
pathology, compared to contemporary cases of T. pallidum
disease, is indicative of yaws (Rothschild et al. 1995:
343). This particular find dates to 1.7
million years ago and was discovered in Kenya.
The east African location of this yaws ridden H.
erectus stands as strong support for the existence of this
disease in early human populations. In
addition, the time frame allows for this disease to have been among the
early
modern humans who made their first movement out of Africa and
eventually into
parts of Europe. Another example of
this type of skeletal pathology is that of a H. erectus
femur found in Italy that has been dated to 500,000
years before the present (Rothschild et al. 1995: 343).
This bone exhibits the same type of
thickening that was discovered on KNM-ER 1808, which suggests a yaws
infection. Again, the location of this
find supports that the early moderns had indeed brought disease to
Neandertal
territory.
Yet, this physical evidence can still be
misleading. In the article titled,
"The Osteological Paradox" the authors thoroughly explain how
skeletal evidence can be misinterpreted when accounting for disease
(Wood et
al. 1992: 343). In particular, they
discuss how bone lesions as disease pathology are usually only found in
those
individuals who endured long enough to obtain the bone scarring because
they
were the ones who survived the disease.
The weaker individuals who immediately succumbed to the disease
would
not have had it long enough to develop bone pathologies.
When analyzing the fossil record one needs
to account for these conditions and understand that the individuals
with
pathology may have been the survivors, rather than the casualties of
disease,
and further insight to their cause of death needs to be investigated. The lack of skeletal evidence for disease in
Neandertal populations is consistent with the possibility of rapid
death from
the introduction of novel diseases. In
addition, the aforementioned skeletal evidence stands as possible proof
that
the T. pallidum diseases existed
among their population and may have contributed to the Neandertal's
demise. Regardless of whether the
lesions were indicative of disease survivors, the point remains that
the T. pallidum diseases were present and
could possibly have been brought in by early modern humans.
There also exists pathological evidence
in the
skeletal remains of more modern humans that may suggest what might be
found in
further Neandertal research. Because
bacterial infections, rather than viral, are more likely to affect the
skeleton, Tuberculosis can be attributed to certain remains (Verano
1992:
6). Tuberculosis erodes bone tissue and
usually affects post-crania; however, the bacteria can spread through
the
circulatory system to other parts of the body such as the legs bones
(Larsen
1997: 99-100). For instance, many
skeletal remains (including mummies) from ancient Egypt show
pathological signs
of Tuberculosis. Several of these
skeletons display a projection at the upper spine, resulting from the
erosion
and collapse of several vertebra forming a hump known as kyphosis. This is indicative of Tuberculosis (Filer
1996: 67-69). Again, these examples are
of more modern times than those addressed in this paper.
However, these illustrations suggest what
might exist in Neandertal fossils that have yet to be discovered.
The paucity of skeletal evidence does
not
necessarily minimize the occurrence of disease; rather its absence
could either
represent diseases that do not damage the bone such as V.
zoster or simply that our sample assemblage of Neandertals is
too narrow to actualize the extent of malady among them.
Adaptations
against disease
The co-evolution of humans and pathogens
has been an ongoing battle for millions of years. Due
to this enduring conflict, humans have evolved adaptations to
combat certain pathogens, typically those that have been among us for
millennia. These adaptations provide an
advantage against the pathogen and have allowed for certain populations
of
people to live surrounded by disease.
One of the most compelling examples is
the
adaptation against malaria that allows for sickle cell anemia. A particular gene alters the shape of red
blood cells that inhibits the malarial plasmodia from entering the cell
(Nesse
et al. 1995: 99). However, an
individual who receives this gene from both of his parents, thus
homozygous
recessive, will be born with sickle cell anemia – a fatal disease. Even with what is a serious disadvantage,
this adaptation is still selected for in malaria prone areas.
There are speculations that an
adaptation for
protection from Tuberculosis also exists.
Tay-Sachs disease is common among Ashkenazic Jews from Eastern
Europe. Those homozygous for the gene
die at a very young age; however, the heterozygotes appear to have a
reproductive advantage. Therefore, the
Tay-Sachs gene is retained within the gene pool (Nesse 1994: 100;
Diamond 1989:
77). The reproductive advantage would be
in the form of protection from Tuberculosis, which was extremely common
among
the crowded neighborhoods of the Ashkenazic Jews over the past several
hundred
years (Ridley 2000:191). Although this
theory remains speculative and deals with modern populations I apply it
here as
an example of how populations can evolve certain adaptations in dealing
with
their environment.
If the early modern humans had been
living among
certain pathogens for long periods of time they may have evolved
adaptations
that protected them – giving them an advantage over the Neandertals. Within the population of early humans there
may have been individuals with the advantage and who were less
susceptible to
the disease, the recessive homozygote individuals, and then further
individuals
who were homozygote dominant who would be neither – therefore, the
likely candidates
to carry the disease, spreading it among the Neandertals.
These modern populations would benefit from
this adaptation while the Neandertals would be left totally susceptible
to the
new disease.
Conclusion
Throughout the fossil record from roughly
120,000 until about 28,000 years ago abundant archaeological and fossil
remains
support the existence of the Neandertal.
However, it is after this point that their tool culture and
skeletal
remains seem to disappear. The
vanishing of the Neandertals appears to take place within the several
thousand
years of the early modern humans occupation of the area.
Although, in certain locations they
cohabited, there came a time when one group eventually prevailed. The Neandertals disappeared from the
archaeological record whereas the modern humans continued on and
thrived with
improved technology. There needs to be
further explanation for this extinction.
Although several theories exist, additional accounts can provide
a more
thorough understanding of the Neandertal's end. The
previous argument detailed a number of important points
supporting the hypothesis of disease as a factor in the Neandertal's
demise.
The Neandertals had evolved
morphological
adaptations to their environment that suggests a long period of
residence in
their homeland. Therefore, factors
leading to their extinction would have had to been extreme and not
particularly
due to only one independent cause.
Diseases have severe effects on populations today, which makes
it a
considerable alternative for the Neandertals.
Several possible diseases are characterized by their ability to
subsist
among small populations like the Neandertals would have been living in. Syphilis and its predecessors are key
culprits in this argument because of their adjustability to varying
climates. Both V. zoster
and Tuberculosis are also potential diseases, due their
simple mode of transmission and extended periods of latency. Given the ease with which diseases can cross
the species barrier, this argument can apply regardless of ones
orientation
towards the relationship of Neandertals to modern humans.
Again, it is important to understand how
devastating novel diseases can be when introduced to virgin populations. The illustrations provided should be clear
indications of how disease can severely impact a population and
ultimately
bring a group of people to near extinction.
Skeletal evidence is provided as proof
that the
syphilis diseases were present during the time of early modern human's
entry
into parts of Europe. In addition,
pathological evidence of Tuberculosis in more recent times is used as a
sign of
what might exist in fossil remains yet to be discovered.
In order to explain why the incoming humans
were not impacted as drastically as the Neandertals by the disease, one
needs
to understand the role of balanced polymorphisms. Certain
populations evolve adaptations to diseases that remain
prevalent among them for long periods of time.
These populations become either resistant or partially immune to
the
pathogens, hence giving this particular group an advantage over those
who were
without the immunity. Had these
diseases originated in Africa among the early modern humans they may
have
evolved these adaptations that would have prevented them from
succumbing to the
disease as rampantly as the Neandertals.
These key details present a valid and
alternative argument to explain the weakening and ultimate decimation
of the
Neandertals. As repeated throughout the
paper, this hypothesis is not intended to explain the entire
disappearance of
the Neandertals. Rather it argues that
disease stands as one of the many factors involved.
The compelling evidence presented supports a supplemental
explanation that will hopefully allow for similar ideas to be addressed
in future
research of the Neandertals.
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