For decades, scientists have been fascinated by how living things evolve new traits — especially the traits that allow animals to reproduce successfully. A new study from the lab of UC Irvine’s Professor Jose Ranz, published in Proceedings of the National Academy of Sciences, offers a fresh look at one of biology’s most mysterious frontiers: the evolution of reproductive proteins. By uncovering how age influences the properties of genes in the fruit fly’s seminal fluid, the research provides vital insights into how life diversifies and adapts over time.
When animals mate, it’s not just sperm that’s transferred from male to female. A complex mix of proteins, known as seminal fluid proteins, travels along too, triggering powerful physiological and behavioral changes that affect fertility, competition and even species evolution. For years, scientists believed that the genes encoding these proteins were mostly “young” and fast-evolving — products of recent evolutionary innovation. But Professor Ranz and his collaborators at the University of Winnipeg discovered that this view tells only part of the story.
By tracing the evolutionary origins of more than 350 seminal fluid protein genes in Drosophila melanogaster, the common fruit fly, the researchers found that nearly two-thirds of these genes are far older than previously thought — predating the emergence of the Drosophila genus itself. These ancient genes play broader roles in the organism’s biology and are deeply connected to other genetic systems, affecting multiple biological processes across the organism. They evolve slowly, in part because their wide-reaching influence leaves little room for drastic changes. In contrast, the younger genes, while fewer in number, evolve rapidly and cluster in tightly connected networks focused mainly on reproduction. These younger genes may be the “innovation engines” of evolution, allowing species to adapt quickly to new environmental and reproductive pressures.
This discovery challenges long-standing assumptions about how reproductive systems evolve. It suggests that evolution doesn’t just rely on the creation of new genes; it also depends on how old and new genes interact, with ancient ones providing stability and younger ones driving innovation. Understanding this interplay could have ripple effects beyond the fruit fly. Because many reproductive proteins play similar roles across species, this research helps shed light on fertility, reproductive health, and biodiversity. It also strengthens the idea that studying the evolutionary “age” of genes can reveal hidden patterns potentially relevant to agriculture, conservation and medicine.
Professor Ranz’s team has shown that biology is more than a catalog of parts; it’s a story of continuity and change, written across millions of years. As genomic tools improve, similar analyses could reveal how ancient and modern genes interact in humans and other animals, unlocking new strategies for preserving fertility, protecting species and even understanding how evolution equips life to persist under constant change. Continued investment in this kind of foundational research will deepen our grasp of life’s complexity and may one day help us solve pressing challenges in health, reproduction and sustainability.