The particular bug is called
shigella flexneri, and was isolated from a British soldier named
Ernest Cable in 1915 during WWI, when he died in a hospital in France from dysentery, which killed a lot of soldiers.
This specimen was tucked away at Porton Down until about a decade ago when one tube of the samples was pulled out, thawed, regrown in a laboratory by a team of scientists led by one Kate Baker, and its genome examined. Lo and behold! One of the things they found out about this 1915 sample of bacteria was that it was already resistant to penicillin. People said, “Woah, wait a minute! Penicillin hadn’t even been
discovered yet!” Its use against bacteria was not discovered until the late 1930s and not put into medical use until the early 1940s. But here was a bug killing a British soldier back in 1915 that already had resistance to that anti-bacterial substance,
penicillium.
One of the key concepts you explore is “horizontal gene transfer.” Give us a layman’s explanation of what this is, with reference to the strange phenomenon of “kissing bugs.”
Horizontal gene transfer is essentially sideways heredity. It’s the passage of genetic material sideways, from one creature into another, from one species into another. It can even go from one kingdom of life into another, sideways, across great barriers. That was thought to be undoable. I first read about it back in 2013 and my reaction was, “Wait, what? No! That doesn’t happen! That
can’t happen!”
In fact, genes
can go sideways across vast species boundaries. For instance, a gene for resistance to one kind of antibiotic in one form of bacteria, like
staphylococcus, can move sideways into another, completely different form of bacteria, say,
E.coli. This can happen not just in bacteria but also in animals, plants, and higher organisms, generally as a result of infection or parasitism.
One example is a form of
transposon. Big, complicated word. [laughs] What’s a transposon? It’s a stretch of DNA that transposes from one part of a genome within a creature to another part. But scientists have discovered that these things can also jump from one creature to another, and even from one
species to another.
One transposon has been given the name
space invaders. It’s a long stretch of DNA that invades lots of different organisms. It seems able to pass, for instance, from a reptile into an insect or from a possum into a rat, by way of something called a kissing bug, an insect that, when sucking blood, su cks in some of this transposon. The transposon then moves from one species to another and becomes part of the heritable genome of that new species.
A 2009 headline in the British magazine New Scientist said “Darwin was wrong” and was immediately seized upon by creationists. Explain the issues and how the latest science is rewriting the idea of natural selection.
It’s not rewriting the idea of natural selection. Rather, it’s rewriting our understanding of evolution, of which natural selection is still a very important part. There are two phases in classic Darwinian evolution. First, there is the arising of variations from one creature to another or one individual population to another. That was thought to occur incrementally, in very slow stages, by mutations in the genome. Once there are variations among individuals, natural selection, the survival of the fittest, acts upon those variations.
What is new, and caused
New Scientist to run that over-stated and provocative headline, “Darwin Was Wrong,” is that
we now understand there is another, hugely significant form of variation. It’s not just incremental mutation, but horizontal gene transfer, bringing entirely new packages of DNA into genomes.
One of the axioms in Darwin’s day,
natura non facit saltus, which your good Latin training [laughs] will tell you means nature does not make leaps; things happen incrementally. But horizontal gene transfer has revealed that
nature does sometimes make leaps, whereby huge lumps of DNA can appear in an individual or population quite suddenly and then natural selection acts on them. That can be a very important mechanism in the evolution of new species.
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