And it brings up the disagreeable subject of anal intercourse. That�s because a striking contrast between simians and humans is that simian species copulate from the rear while humans usually copulate from the front. Anal intercourse is known to be one of the most severe risk factors for HIV infection. And it woud seem that simian-style copulation has a much greater risk for accidental anal copulation than human-style copulation.
Indeed, that difference in the manner of intercourse could explain why the human species has been relatively free of HIV infection. And that would, in fact, justify, at least in one certain respect, the implicit assumption of our journal authors that humans have been comparatively HIV free in the past.
But anal intercourse wasn�t absolutely unknown to humans before 1900. That fact is known from various historical writings. So it seems quite possible that there�s been a certain incidence of HIV in the human population for a long time, but at a lower level than for SIV in chimps and other simian species.
There�s a feline version of the virus, �FIV.� Felines also copulate from the rear. Like HIV, FIV was only recently discovered. But scientists don�t assume that FIV has only recently come into existence simply because it was only recently discovered. However, that assumption is being made with HIV.
It seems a fallacious assumption.
One salient fact here is that there is no canine immunodeficiency virus--or , at least there's no cannine equivalent of AIDS. The manner in which dogs copulate is quite different from cats and probably explains the difference. It would be easy to determine from experiments whether anal insemination of mammialian species that don't have naturally-occuring immunodeficiency disease can produce such diesase in the laboratory.
Imagining a cross-species jump for HIV may be a psychological mechanism to shift the �blame� for HIV elsewhere--to another species. After all, science itself is partly to �blame� for AIDS. Blood transfusions and medicines made from blood plasma weren�t introduced until after World War II. For a period of time, circa 1980, that technology proved ideal for spreading HIV. �Blame� is in quotes because not even the smartest, most conscientious scientist, circa 1955, could have imagined what was to transpire in later decades. But scientists would like to forget their own falability. Ascribing the origin of the HIV epidemic to cross-species transmission might be a denial mechanism.
[ 10 ] An alternate origin for HIV
�Forty-five percent of the human genome consists of remnants of previous transposon/virus invasions and elements that are still active to date: 21% long interspersed nuclear elements, 13% short interspersed nuclear elements, 8% retroviruses, and 3% DNA transposons.�
That�s according to Ronald H. A. Plasterk. His paper �RNA Silencing: The Genome�s Immune System� was in Science 17 May 2002 (p1263).
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