For over a century, scientists have assumed that animals evolved multiple types of light-sensitive cells in the eye specifically to see in colour—but this project argues that colour vision was actually a latecomer, a secondary benefit of circuits that originally helped ancient fish detect motion, hunt prey, and escape predators. The research challenges a foundational assumption in visual neuroscience. If correct, it would rewrite our understanding of how vision evolved and how the brain processes what the eye detects. The team will test this by genetically manipulating zebrafish—which retain the full set of ancestral photoreceptors—and recording how different cone types drive specific behaviours like swimming toward prey or dodging a threat. This is fundamental science, not applied technology. There is no immediate practical application. But understanding the ancestral wiring of vision could eventually inform artificial vision systems, retinal prosthetics, or computer vision algorithms that mimic biological motion detection. Past discoveries about how the retina processes information have already shaped everything from camera sensors to medical imaging.
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Colour vision is based on comparing signals from different photoreceptors, but we have long reverted this correspondence: The purpose of having multiple types of photoreceptors is to enable colour vision. I challenge this long held notion. I posit that the original purpose of having multiple types of photoreceptors is to serve as parallel feature channels that differentially underpin visual motor programs such as motion vision behaviours, prey capture, or predator evasion. In this view, colour vision is a derived trait that emerged as a secondary benefit of the ancestral circuits that originally supported the first aquatic vertebrates' newfound abilities to visually segment and navigate their underwater world. Specifically, I hypothesise that vertebrate vision was originally built around three main circuits that begin with distinct sets of ancestral photoreceptors: i. Red-cones and rods for general purpose greyscale vision ii. UV-cones for specialised foreground vision iii. Green/Blue-cones for regulating red- and UV-circuits. My project aims to explore this hypothesis through three complementary aims: 1. Understanding what different cones "see," 2. Determining how cone-signals are combined and contrasted in the retina. 3. Establishing the necessity and sufficiency of different cone types for different behaviours. We will combine state-of-the-art approaches in high-throughput neurophysiology and visual stimulation with genetic manipulationof visual circuits, behaviour, computational modelling and field work. All experiments will be centrally rooted in zebrafish, an experimentally accessible species that retains the complete ancestral photoreceptor complement to the present day, and that has a similar visual ecology compared to our earliest vertebrate ancestors where vision first evolved. To test generality, we will adapt key approaches from zebrafish for working with other vertebrate species, including amphibians, mammals and birds.
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