Re: diseases and immunity

Joel and Lynn Gazis-Sax (
Sat, 06 Jul 1996 23:22:34 -0800

Mary Beth Williams wrote:
> In <> Joel and Lynn Gazis-Sax <>
> writes:
> >* That Europeans were exposed to many infectious diseases at an
> >earlier period than the peoples of the Americas.
> >
> >* That this exposure weeded out those less able to withstand the
> >diseases and caused European populations to become more resistant to
> >them.
> Actually, this is both true and false. Yes, the exposure weeded out
> those more suseptible to these diseases -- they died. However, those
> people who actually fell victim to the diseases and survived became
> *resistant* to such only because of the development of immunity through
> prior first-hand exposure, not genetic mutation. Its already been
> discussed that transfer of maternal immunity only lasts for the period
> during breastfeeding (hence, the high mortality of post-weening
> toddlers.) One of the reasons plague was less *successful* in
> subsequent epidemics is that it didn't have *virgin* populations
> through which to pass -- if it hit a pocket of *resistees*, and
> couldn't thus be transmitted, it died out. This is one of the reasons,
> as discussed previously, the smallpox probably didn't often make it
> across the Atlantic until its vector of transmission (kids and/or other
> non-resistees) increased.
> MB Williams
> Dept. of Anthro., UMass-Amherst

You are right! Immunity is not passed on from generation to generation. But
there are other factors which affect how resistant a population is to
disease. I stand by my original statements simply because my concept of resistance
is broader than mere immunity.

We know that when a disease first arrives in a culture, it is devastating. The
effects are far worse on the first generation than it is on subsequent generations.
Two examples: In the South Pacific, when measles first arrived, it wiped out
90% of the population. Measles is a highly infectious disease, but that does
not explain why it killed so many people. Mortality rates for the measles dropped in
subsequent generations, more to the international norm for this disease.

Another example is the Ojibway (?) Indians who were first exposed to tuberculosis
in the early twentieth century. At first, when the disease hit, *nobody knew
what it was*. It did not act like normal tuberculosis which forms tumors in the
lungs. In the first generation of Ojibway TB victims, tumors formed in the brain,
liver, and all over the body! It was only by examining the tumors under a microscope
that the cause was recognized as TB. Again, in subsequent generations it
resembled the TB we all know and love. (Note that while immunity can be formed
to TB, TB vaccines have never been as effective as other vaccines. The track
record is pretty poor.)

These cases suggest that something other than immunity must be taken into account
when considering the problem of new diseases. European history is also filled
with diseases with strange symptoms that came and disappeared, never to be seen
again. Or were they? (McNall's Plagues and Peoples is an excellent history of
disease which takes up these problems.)

The point I am making is that there appear to be genetic factors beyond immunity
that can affect how a disease infects a body. Certain forms of a disease are
more survivable than others (e.g. TB in the lungs has a higher probability of
survival than TB in the brain or the liver -- the infected may actually live
to breed!). The thesis is interesting and helpful in explaining the massive
depopulation of the Americas when the Europeans arrived.



___ ___
/\ _|_ /\ Joel and Lynn GAzis-SAx
/ /\_|_/\ \
/ / /\|/\ \ \
\ \ \/|\/ / / "If we try to flee from our human condition into
\ \/_|_\/ / the computer, we only meet ourselves there."
\/__|__\/ William Barrett