Unscrambling the egg
Under a microscope, Dr. Brian Hall studies the deformed beak of a three-day-old chick embryo. Most observers would see lost future potential in this fledgling. Dr. Hall stoops closer to see and better understand the past – the evolutionary history of not just this chick, but all vertebrates. His ability to synthesize past and present has made him a global trailblazer in the field of skeletal development and in the burgeoning field of evolutionary developmental biology (or evo-devo to its practitioners).
Charles Darwin anticipated that developmental biology would provide the most fertile ground for understanding how body structures change through evolution. But for most of the 20th century, scientists focused on either developmental or evolutionary biology, with little cross-fertilization.
This began to change in the early 1970s, just as a young Australian developmental biologist was beginning his career. In the mid 1970s, Dr. Hall demonstrated how embryonic movement causes stem cells on developing bones to switch from bone to cartilage formation. It was the beginning of 35 years of groundbreaking research exploring the evolution and formation of skeletal tissues, particularly those of the face (and skull and gills in fish). It's research that has provided key clues to how bone is lost during inactivity or prolonged bed rest.
Characteristic of Dr. Hall's wide-ranging curiosity, his extensive comparative skeletal development experimentation led him to burrow down into cellular minutiae, and then to come up to see this detail as part of the larger landscape of life across time.
To understand the origins of facial skeletal tissues, Dr. Hall turned his attention to the neural crest cells. These are a group of embryonic cells that originate in the developing nervous system, but migrate to form bones, cartilage and teeth in the head. Through meticulous research tracking the cellular interactions that "switch on" these cell types, he provided fundamental insights into the now headline-grabbing subject of cellular differentiation. His book The Neural Crest (1988) is already considered a classic text on the subject.
His lab's research demonstrated how particular clusters of neural crest cells produce specific facial structures. This work is critical to understanding the causes of – and perhaps treating – congenital facial and dental deformities, including cleft palate.
In a pioneering 1973 paper, Dr. Hall described the evolution of skeletal tissues. Since then he's been at the forefront of efforts to explain the role of developmental modifications as a factor in evolution, including writing a seminal text on the subject, Evolutionary Developmental Biology (1992). As such, he's drawn on his rich experimental experience to challenge long-held canonical concepts in biology. For example, homology (similarity) of structures between different species has long been considered definitive evidence of common ancestry. But Dr. Hall has shown that many structures currently deemed homologous in fact arise from different developmental processes.
Now he's taking the next step to combining past and present – he's establishing one of the world's few labs that combines embryologists, paleontologists, and evolutionary biologists. Together they are asking not whether the egg or chicken came first, but how they evolved together.
Brian Hall, FRSC
George S. Campbell Professor of Biology