Fluffy Koala or slimy Earthworm? Which one’s feelings or emotions are you better able to understand? If both were in danger of death, which one would you save? Questions like these were posed to 3,509 study participants in a recent online survey in France. The study was carried out by evolutionary biologists, who wanted to find out more about our empathy and compassion towards different living creatures.

While it’s already known that we prefer animals who look, think, and act like us, past studies into this phenomenon didn’t consider the role of “phylogenetic distance.” Does it matter how long ago our evolutionary paths separated and how far we’ve developed since? Furthermore, previous studies mainly looked at mammals. But what about our empathy and compassion towards more distant species, such as reptiles, fish, birds, insects, mollusks, plants, or even fungi?

To test the hypothesis that our feelings towards different creatures depend on evolutionary distance, the researchers in this study selected 52 species that were representatives of different taxonomic groups, i.e. groups that diverged from the human lineage at different time points (47 animals, four plants, and one fungi). They randomly selected pictures of two of these species at a time and asked the participants to weigh one against the other: Which species’ feelings are they better able to understand (assessing empathy) and which one would they save (assessing compassion)? The probability of one species to be chosen over all others was then used as a measure of our empathy and compassion towards them. The researchers also assessed differences in the study participants’ sex, age, knowledge on biodiversity, opinion on hunting/fishing, and opinion on the value of animal life relative to human life. These factors significantly influenced the participants’ answers and were therefore accounted for in the analysis, so that they didn’t confound the results.

As expected, the empathy and compassion scores of a species decreased gradually with its evolutionary distance to us humans. We tend to save the life of an Orang-Utan, one of our closest relatives, with higher probability than the life of an antelope. This finding may not be surprising, or may even seem obvious. After all, the closer we are evolutionary, the more similar we are. Human-like features, such as having two forward-facing eyes, being able to walk on two limbs etc., might speak to the same neuronal circuits of empathy and compassion that are usually activated by fellow human beings.

However, the finding of a gradual decrease along evolutionary lines is quite interesting, if you think about how often we draw clear-cut boundaries between different beings. For example, pescatarians think differently about fish vs. other animals, and animal welfare laws often distinguish between vertebrates and non-vertebrates. Based on these oppositions, one could have expected to see steeper drops in empathy and compassion at certain points of the evolutionary timescale. Instead, the change was gradual. This indicates that the oppositions that we often make in everyday life are not reflected in the empathy and compassion that we feel towards different species in our minds (and perhaps our hearts).

Still, there were some note-worthy exceptions to the general trend. The Oaktree, Beluga whale, and Earthworm, for example, received far more compassion than expected by their phylogenetic distance to us. In contrast, ticks were incredibly unpopular and received very low levels of empathy, probably due to their parasitic lifestyle and spread of a disease that greatly affects humans. There was also a general tendency to favor large organisms over small ones.

Lastly, at a certain point, more evolutionary distance did not lead to less empathy and compassion. What marks this stopping point, after which all living creatures seem somewhat equally unrelatable to us? In this study, it coincided with the evolution of “bilateral symmetry.” Simply put, animals without bilateral symmetry don’t have a clear front and back, back, and belly. Think of sponges or jellyfish. It seems that we find it difficult to relate to species that are so different from us that we can’t even clearly recognize a front and back.

The authors emphasize that these findings need to be treated with caution, and future studies will have to show whether it’s reproducible. In addition, it would be interesting to see whether the same results would also be obtained when repeating the study in other cultural contexts. If this were the case, that would be a very strong argument for the biological underpinning of our feelings towards different beings, irrespective of the culture and norms that we grew up with. Altogether, this is one of the first studies to explicitly show that a biological component, i.e. phylogenetic distance, may underlie our preferences for different living creatures. Animal advocates need to keep these underlying dynamics in mind in their work, whether for wildlife, companion animals, farmed animals, or any other species.