Dopamine. This neurotransmitters is well known for being involved in processing reward. I recently read about dopamine being used for something similar in a fruit fly, so I tried to look up if maybe dopamine use is evolutionary conserved. First, multiple introductions from studies using fruit flies suggested conservation [ex: 1]. So I then I looked for the common ancestors for flies and mammals to learn about its brain.
A quick google search revealed that an urbilateria was the last common ancestor for flies and mammals was from 500-600 million years ago. Although the details of what this organisms was like differ, they are thought to have been worm-like with a rudimentary nervous system of some sort (clusters of neurons with ganglias and/or brain vs. diffuse network) [2]. I couldn’t find much information on the details of this ancient brain, but I thought that if dopamine use was conserved from this division, then maybe current animals that share the common ancestor would also use dopamine in reward related behaviors.
C. elegans are small worms that also share the common ancestors and have 8 dopamine neurons. Some evidence suggest involvement of dopamine in assessing food information (volume of food) [3]. I realized that assessing reward and preference in worms would be difficult, even odd, but (a) the presence of dopamine suggests that the neurotransmitter evolved before urbilateria and (b) maybe dopamine has had a role in reward then too and has been conserved.
Obviously, dopamine use in more animals need to be compared to make an assessment about the origin of dopamine. But I thought that it was interesting how a common ancestor from so long ago might have also used dopamine for some behavioral processing and it has been used since.
[1] PMID: 26687359
[2] PMID: 24098981
[3] PMID: 25864633
Originally posted on Instagram April 2, 2019
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