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#1 Disease outbreaks risk extinction
Yule ’13 (et al; Jeffrey V. Yule – Herbert McElveen Professor of Applied and Natural Sciences At the School of Biological
Sciences, Louisiana Tech University, Published April 2nd – Humanities 2013, 2, 147–159; doi:10.3390/h2020147)
Since the 1940s, humans in industrialized nations have been relatively sheltered from the threat that
infectious disease once posed. Modern antibiotics and antivirals have controlled pathogens that
once devastated human populations, but these drugs often remain effective only briefly.
Unprecedentedly large, dense human populations characteristic of modern societies coupled with rapid global travel
create a situation in which emerging pathogens can move much more efficiently between hosts.
Rates of future human mortality from emerging infectious diseases may depend on the levels of
biodiversity that remain in unpopulated regions, which suggests that protection from novel infectious disease
may be what has been, until recently, an overlooked benefit of biodiversity. We have assumed that
humanity’s future will unfold in a way that avoids any of a number of global disasters for Homo sapiens
sapiens. An equally reasonable but less optimistic assessment could take exception to that position. A
variety of things could go badly wrong for humanity. Global human N may not stabilize at or below where it stands
now without being pushed there by some form(s) of crisis that result from humans exceeding global K. As a result, anthropogenic
factors from the intentionally harmful (e.g., warfare) to the unintentionally disastrous (e.g., agricultural practices leading to topsoil
erosion and desertification) could occur singly or in conjunction with one another, with a variety of natural disasters (e.g., volcanic
eruptions, earthquakes), and with disasters that straddle the boundary of natural and anthropogenic, the sorts of scenarios that
otherwise could have been avoided or their impacts lessened with more forethought (e.g.,
outbreaks of infectious
disease that move easily through dense human population centers and cannot be readily
treated due to pathogen drug resistance). Although we cannot rule out such eventualities, speculation about
the future of humanity is inherently more interesting if it proceeds on the assumption that the
species will be at least moderately successful beyond the short- to medium-term. However, it may not,
and the potential failure of our species has considerable biological implications.
#2 Diseases won’t cause extinction – burnout or variation
York ‘14 (Ian, 6/4 head of the Influenza Molecular Virology and Vaccines team in the Immunology and Pathogenesis Branch,
Influenza Division at the CDC, former assistant professor in immunology/virology/molecular biology (MSU), former RA Professor in
antiviral and antitumor immunity (UMass Medical School), Research Fellow (Harvard), Ph.D., Virology (McMaster), M.Sc.,
Immunology (Guelph), “Why Don't Diseases Completely Wipe Out Species?” 6/4, http://www.quora.com/Why-dont-diseasescompletely-wipe-out-species#THUR)
But mostly
diseases don't drive species extinct. There are several reasons for that. For one, the
most dangerous diseases are those that spread from one individual to another. If the disease is
highly lethal, then the population drops, and it becomes less likely that individuals will contact
each other during the infectious phase. Highly contagious diseases tend to burn themselves out
that way. Probably the main reason is variation. Within the host and the pathogen population there will
be a wide range of variants. Some hosts may be naturally resistant. Some pathogens will be less
virulent. And either alone or in combination, you end up with infected individuals who survive.
We see this in HIV, for example. There is a small fraction of humans who are naturally resistant or altogether
immune to HIV, either because of their CCR5 allele or their MHC Class I type. And there are a handful of people who were
infected with defective versions of HIV that didn't progress to disease. We can see indications of this sort of thing
happening in the past, because our genomes contain many instances of pathogen resistance genes
that have spread through the whole population. Those all started off as rare mutations that conferred a strong selection
advantage to the carriers, meaning that the specific infectious diseases were serious threats to the species.