In Embryos under the Microscope: The Diverging Meanings of Life, biologist Jane Maienschein gives us a thoughtful and historically contextualized look at embryos so as to better inform conversations that are too often clouded by politics. Scientific knowledge can and should affect our policy and social decisions, she argues, even when the science alone does not tell us what those decisions should be. In the conversation below, Maienschein outlines some of what we now know of embyros, and stresses the importance of allowing that knowledge to supplant conflicting assumptions about the workings and meanings of life.
Q. Since before Aristotle cut open a developing chicken’s egg, scientists and theologians have theorized about embryos they couldn’t see. How does speculation about “invisible embryos” continue to shape contemporary thinking?
Most people have never seen an actual embryo, nor seen one develop from a fertilized egg cell. For them, embryos are largely “invisible” and imagined. Many people imagine a tiny person somehow there inside a woman who has just gotten pregnant, for example, and they imagine it as just growing larger over time. Yet in humans, the fertilized egg becomes an embryo and is called that until it is 8 weeks old; an embryo is not yet formed as a fully formed individual. Only after 8 weeks is it called a fetus, because it has the basic structure, the most important organs, and the very beginnings of the functioning of the human organism. Without knowing these developmental stages, and without actually seeing—through models or under a microscope—we are left to imagine what the invisible embryo looks like and how it behaves.
Q. What do the major advances in embryology over the course of the 20th century suggest about the trajectory of future science?
The case of embryo research shows how science is surprising and exciting in so many ways. Old assumptions give way to new knowledge, which leads to new insights and discoveries. The path is not always linear, and sometimes researchers get stuck in a way of thinking that takes a while to rethink. For example, most 20th-century researchers thought that once a cell becomes differentiated in a certain way, it will be fixed or determined in that way forever. We have learned that it is not that simple and that de-differentiation and re-differentiation is possible—with great potential for regenerative medicine. What history shows is the importance of becoming aware of underlying assumptions and rethinking them.