On page 118 Dr Moalem states diseases that require "close
proximity that allows for transmission through the air or physical
contact" are at an evolutionary disadvantage if they kill their hosts.
Yet the smallpox virus, which originated in Africa, spreads in this way,
and is infamous for killing its host.
What adaptation does smallpox have that allows it to kill it's
host still spread throughout a population? What selective pressures did
Africa provide that caused smallpox to evolve the way it did?
This question relates to Big Idea #1 (the process of evolution drives
the unity and diversity of life) because smallpox evolved some
adaptation that allows it to kill a host and continue spreading, an
adaptation that resulted from it's origin in Africa.
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ReplyDeleteWhen a deadly disease is endemic in a population, over many generations, the population gradually builds up a resistance to it. Most serious diseases are especially likely to kill the weak hosts. For example, children who die of a disease obviously won’t live to reproduce. However, some people have combinations of genes that help their immune systems to successfully fight particular diseases. A child who survives smallpox and grows up will pass on his smallpox-resistant genes to his children. Since people with genes that help them resist the endemic disease are more likely to live, reproduce, and pass on their genes, while people who lack those genes are more likely to die in childhood, over time, all of the surviving population will have those genes.
ReplyDeleteHowever, because of these developing conditions, smallpox cells started to go through adaptations: millions of years of evolutionary pressure, response, adaptation, and selection come together in that first cell; it contains every single genetic instruction to manufacture the proteins used to build a human being. Outbreaks and pandemics, such as smallpox, are thought to be caused by antigenic drift, when a mutation occurs in the DNA of a virus, or antigenic shift, when a virus acquires new genes from a related strain. When the antigenic drift or shift in a virus is significant enough, our bodies don’t recognize it and have no antibodies to fight it, which causes our body get penetrated by smallpox virus (131).
According to the researchers, high frequency of the variant in Europe arose through strong selection from bubonic plague has become known as the signature of historical selection; this assertion has been gaining widespread acceptance in both population genetic and medical literature, despite the absence of quantitative assessment. If we believe this assertion, then those who didn’t go through the plague-- essentially including African, Asian, Middle Eastern, and American Indian populations. These evidences indicate that the smallpox virus is a more likely candidate: predictions from a population genetic model and the geographical distribution of the allele. This idea relates to big Idea 1 (the process of evolution drives the unity and diversity of life); in addition, the fact that smallpox developed adaptation to survive and reproduce relates to the big idea 1.
(Hyung Eun Lee, helee4@students.d125.org)
Additional sources:
http://www.learnnc.org/lp/editions/nchist-twoworlds/1689
http://www.pnas.org/content/100/25/15276.full