He was a pioneer in the science of teratology, in particular the study of birth defects and abnormalities that occur during embryonic development. He believed that abnormal development adhered to the same natural laws as did normal development. With French embryologist Étienne Serres (1786–1868), the "Meckel-Serres Law" is named, defined as a theory of parallelism between the stages of ontogeny and the stages of a unifying pattern in the organic world ("scala naturae").[1]