Bioethics Blogs

Is this really me? Parasites and other humans’ cells in our brains change our psychology

Many people are suspicious about being manipulated in their emotions, thoughts or behaviour by external influences, may those be drugs or advertising. However, it seems that – unbeknown to most of us – within our own bodies exist a considerable number of foreign entities. These entities can change our psychology to a surprisingly large degree. And they pursue their own interests – which do not necessarily coincide with ours.

In their highly recommendable paper “Humans as Superorganism: How Microbes, Viruses, Imprinted Genes, and Other Selfish Entities Shape Our Behavior”, published in Perspectives on Psychological Science this week, Peter Kramer and Paola Bressan make a convincing case that we human beings are not unitary individuals, but superorganisms – “collections of human and non-human elements that […] jointly define who we are.”

They describe a variety of foreign entities we coexist with and how they can influence our behaviour. I want to give two astonishing examples here: microbes and body cells of other human beings.


Human cell infected with Toxoplasma gondii

There are microbes that have specialised on living as parasites in the brains of animals, including us. One such microbe parasite is Toxoplasma gondii.

Typically, Toxoplasma’s aim is to get into cats, where it can reproduce and lay eggs in their intestines. To achieve this, Toxoplasma goes via rats, which serve as so-called intermediate hosts. When a cat eats an infected rat, the parasite gets passed on to the cat. So Toxoplasma manipulates the behaviour of rats such that the probability of being eaten by a cat increases.

The views, opinions and positions expressed by these authors and blogs are theirs and do not necessarily represent that of the Bioethics Research Library and Kennedy Institute of Ethics or Georgetown University.