Why being parasitized is a normal part of life
In short: Parasites are ubiquitous, found in almost all animals and plants. In fact, being parasitized is a natural state for most organisms. It is only in WEIRD—Western, Educated, Industrialised, Rich, Democratic—societies that people typically lack many parasites, a shift that may actually cause biological systems to go awry.
In his lecture for Gresham College, Professor Mark Viney explores the profound evolutionary impact of parasites. These organisms are specially adapted to live inside other animals, and this intimate relationship has shaped the very evolution of their hosts. While we often view them through a lens of disease, parasites are a fundamental component of the natural world.
Defining a parasite requires navigating a complex continuum of biological associations. On one end of this spectrum are mutualism, commensalism, and symbiosis, where the association does not cost the host anything more than the host gains. In these relationships, the host at least performs as well as it would without the other organism present.
Parasitism is distinct because it is defined by harm and loss; the host loses while the parasite gains. In a zoological context, this definition can be difficult to draw precisely, as the line between these different types of associations is somewhat arbitrary. These parasites can inhabit a wide range of multicellular animal hosts, from mammals and vertebrates like birds, fish, reptiles, and amphibians, to invertebrates such as insects, slugs, and snails.
The absence of these organisms in modern, developed societies is a significant biological shift. Because animals, including humans, evolved in the constant presence of parasites, our biological systems can sometimes malfunction when they are no longer present. This raises a provocative question: if being parasitized is the natural norm, should we be looking to embrace them?
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Sources
- Summary by Intellect · source: The Parasite Zoo - Professor Mark Viney
- Also: The Parasite Zoo
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