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The Problem with Parasites December 12, 2010

Posted by Metabiological in Ecology, Ethics.
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David Pearce is fond of saying that the last instance of suffering in the world will be a datable event. As a supporter of the Hedonistic Imperative I believe it is humanities destiny to accomplish this. However as a student of ecology I am also more than aware of the monumental proportions of the task that lay before us. To not only eliminate suffering but to do it in a way that results in a functioning, self-sustaining ecosystem (there are reasons to do it this way that I will come back to another day) is a task that will take resources, planning and time almost beyond comprehension. I offer one small segment of the problem here: the problem with parasites.

Parasites, even more than predators, are the ultimate challenge to HI. From a strictly logistical standpoint they present far greater difficulties. Firstly, they are generally much smaller. This may sound obvious but the macro scale of most of the worlds predators makes them easier to deal with. Large animals can be tracked, observed and altered with far less difficulty than tiny ones, let alone microscopic ones. Secondly, there are far more parasites in the world than predators. This is related to the first point in that you can fit far more smaller animals into an ecosystem than you can larger ones. Thirdly, parasites are not always obvious. A predator stalking, killing and devouring an organisms leaves tell-tale clues behind (the most obvious of which is a corpse) that are easy to comprehend. Even when direct evidence of predation cannot be found it can be inferred through indirect methods such as large scale changes in the population density or distribution of the prey. Parasitism does not always present such a clear case. Though many parasites can certainly be detected through their negative effects it is not always as clear what is causing the problem. Often times the only sign that a parasite is present is during a autopsy.

It is not simply logistics that make parasites our greatest obstacle. The suffering caused by parasites is far greater than that caused by predators. Though terrifying, predation at least ends the suffering of the prey, albeit through death. Parasites by comparison can be present for years, in some cases throughout the whole natural lifetime of the organism. This is without discussing the subject of parasitoids, creatures that lay there eggs within the bodies of their hosts. Anyone who has watched a tarantula being eaten alive from the inside out by a wasps larvae cannot help but shudder.

So how to we fix this problem? One solution is to simply wipe parasites out. Others have considered the controlled extinction of certain species as a means to reduce suffering and though at first glance it may seem crazy it is not as outlandish an idea as it may seem. Many mosquito populations have already been eradicated through the use of pesticides such as DDT to prevent the spread of malaria. Unfortunately, these actions have met with varying and limited degrees of success with the biggest problem being the evolution of individuals resistant to the effects of the pesticides. For this reason and the shear logistical nightmare of attempting to wipe out every parasitic species on earth we must relegate extinction to nothing more than a situational tool.

A better solution is to use the tools that evolution has already provided for us, namely to shift the relationship parasites have with there hosts. Mutualisms are positive interactions between two or more species that result in a benefit for all individuals involved. Arguably the most common example is between various insect and flower species; the insects receive nourishment from the nectar while the flowers use the insects for pollination. This scenario is well known to even non-experts but mutualisms are far more wide spread than most people realize. Pilot fish eating parasites from sharks, bacteria fixing nitrogen for plants in exchange for food, snails eating the fouling organisms from the algae they live on; each of those and many more is a beneficial interaction that took no human intervention to create.

It may seem at first that transforming a parasitic relationship to a mutualistic relationship would be rather difficult but in this case looks are deceiving. The important thing to keep in mind is that mutualisms are not examples of true cooperation between species. Indeed they are more properly identified as systems of mutual exploitation with the positive benefits merely being a side effect of each species taking what it needs. While the evolution how these relationships developed is not well understood it seems likely that many mutualisms originally evolved out of parasitic relationships.

Critics of HI have noted that any attempt to re-engineer the natural world in the name of eliminating suffering will require massive top-down regulation and control, with all the problems associated with such systems. While one can argue the degree to which this is true it seems likely that to some degree it must be. Our goal then should be to look for any opportunity to let evolution do our work for us, allowing us to merely dip our hand into the stream whenever we need to correct our course.

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