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THE SHARED GENETICS OF PAIN

In biology, homology refers to the similarity of characteristics, such as genes or anatomical structures, that are shared by different organisms as a result of their common evolutionary ancestry. Genetic homology can have "deep" roots, common across the tree of life. For example, HOX genes act as master switches controlling the layout of body plans in animals as diverse as flies and guys.

HOX genes in flies and humans

Genetic conservation is not restricted to coding for overall body layouts. Indeed, what seem like highly complex traits, such as the wide array of eyes found in nature, all rely on a shared genetic master switch. For example, if a gene controlling the development of eyes in flies is deleted and replaced with the mouse version of this gene, one might wonder if the fly would grow small mouse eyes. However, despite carrying the mouse master switch, these flies grow a normal pair of compound fly eyes, like those seen in the image below (WT, Drosophila).

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eyeless and pax6 gene knockouts

As complex as pain and distress are, many genes essential for pain behavior have remained remarkably conserved between humans and other animals. Even in cases where the genetic code has changed significantly, the expression of that code often results in similar amino acid sequences and proteins with essentially the same function.

Experiments have shown that when mutant genetic sequences from pain-insensitive humans are inserted into mouse and fly genomes, they frequently show behavioral signs consistent with what is observed in humans. This is not to say that other animals definitively have the same subjective experiences of pain or suffering, but given that these genetic changes are coupled with similar behavioral effects, the presumption is not unfounded. As Charles Darwin wrote, "The lower animals, like man, manifestly feel pleasure and pain, happiness and misery" (The Descent of Man, p.39).
 

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