Birds and mammals shared a common evolutionary ancestor until approximately 320 million years ago, at which time they then split into two separately evolving groups. That may sound like a long time ago, but this means that mammals are more closely related to birds than to other organisms that scientists use for research such as frogs (which shared a common ancestor with mammals around 350 million years ago), sea urchins (about 550 million years ago), or fruit flies (about 750 million years ago). Because birds and mammals share a relatively recent evolutionary past, many of their physiological and anatomical traits are similar. They also share many of the same developmental processes – the way in which a fertilized egg is transformed into a multicellular, functioning adult. Students enrolled in the SU Developmental Biology course study early chicken embryos to learn about the same developmental processes that we also see in human embryos. Chicken embryos are also much easier to obtain and study than tiny, internally developing mammalian embryos (like those found in mice, another commonly used research animal). By understanding how embryos typically develop and the mechanisms behind that development, scientists can start to pinpoint the causes of birth defects and other developmental issues seen in humans.

A student examines a chicken embryo 72 hours after fertilization. Photo by SU faculty member Heather Brown.