Sea sponges, which are among the simplest animals and lack brains, nerves, and neurons, use sunset as a signal to begin their transformation from free-swimming larvae into adult sponges. A new study published in eLife reveals that environmental cues like sunset play a crucial role in triggering this metamorphosis, helping the larvae prepare for a dramatic change in their life cycle. The research found that sunset causes changes in the sponges’ DNA, allowing them to anticipate the transformation. Scientists used a technique called chromatin accessibility profiling, which identifies regions of the genome that are "open" or accessible, meaning genes in those areas can be turned on. These accessible regions, which contain genes related to settlement and metamorphosis, become activated long before the actual transformation begins. This transformation happens extremely quickly—within about 30 minutes—allowing the larvae to become firmly attached to a surface and start breaking down their larval bodies. This speed is essential for survival, as the larvae are vulnerable to predators and environmental threats during this process. The study suggests that this ability to anticipate and respond rapidly to environmental signals may be a common strategy among many different species. Interestingly, many of the genes involved in this process in sponges are also found in humans. For example, the CLOCK gene, which plays a role in sponge metamorphosis, is also responsible for setting circadian rhythms in humans. Studying sea sponges, which are some of the oldest living animal groups, can provide important insights into early animal evolution and how the first animals learned to use environmental cues to prepare for future events.