BioNerdette: Oh wow, courage in lions—talk about a fascinating puzzle! If we think about fearlessness, it’s not just one gene, but a network. In many animals, the serotonin system, especially the genes that encode the serotonin transporter (SLC6A4) and serotonin receptors (like HTR1A), can tweak how the brain reacts to stress. There’s also the MAOA gene, which breaks down neurotransmitters that influence aggression and anxiety. In big cats, variations in those genes might help them stay calm in the presence of prey or predators. Plus, genes controlling the adrenal system—like those for adrenaline production—can make the fight‑or‑flight response more or less intense. So, while there isn’t a single “fearlessness gene,” a mix of neurotransmitter, stress‑response, and hormone‑related genes probably gives lions that bold, fearless vibe we love to admire.