Periklis Paganos peered through the microscope at a tangle of glowing nerves nestled within the ovary of a bat sea star, and saw something astonishing—not just a map of a marine creature’s reproduction, but a reflection of our own biological past. Though humans and bat sea stars diverged over half a billion years ago, scientists at the Marine Biological Laboratory have discovered that our ovaries share strikingly similar genetics, cell types, and signaling mechanisms. This revelation, published in Nature Communications, suggests that the blueprint for female reproduction is far older—and more universal—than previously imagined.
At first glance, the reproductive lives of humans and sea stars couldn’t be more different. Women are born with a finite number of eggs that mature and deplete over time, while bat sea stars can produce millions of new eggs throughout lifespans stretching up to two centuries, releasing them into the ocean for external fertilization. Yet beneath these contrasting strategies lies a deep evolutionary kinship. Zak Swartz and his team found that bat sea star egg cells are surrounded by granulosa-like support cells—functionally and genetically akin to those in human ovaries—indicating these cells have played a vital reproductive role since before vertebrates even existed.
Using hybridization chain reaction (HCR) microscopy, the researchers mapped the ovary’s structure and identified a network of neuron-like cells forming a nerve plexus in its outer layers. These cells express genes such as gnrh and gnrhr—molecules central to the brain-ovary communication axis in humans and other vertebrates. The discovery suggests that the ovary itself may house an ancient, self-contained neuroendocrine system capable of regulating egg development and release, long before complex brains evolved. "There are lots of animals out there that don’t have a brain but do have an ovary," Swartz explains, "so how do they regulate reproduction in that kind of situation?" The answer may lie within the ovary’s own neural network.
This work not only rewrites our understanding of reproductive evolution but also positions sea stars as a powerful new model for studying fertility and stem cell regeneration. If these animals can continuously generate eggs for centuries, unlocking the genetic and cellular mechanisms behind that ability could one day inform treatments for human infertility or reproductive aging. The shared genetic toolkit—preserved across 500 million years of evolution—hints that the foundations of human fertility are written in an ancient code, still echoing in the depths of the ocean.
As scientists continue to decode this primordial script, the bat sea star emerges not as a distant oddity, but as a quiet guardian of secrets about our own bodies—reminding us that even in the most alien forms, we can find pieces of ourselves.