Why can minor physical anomalies have both genetic and environmental influences?

Minor physical anomalies arise during phenogenesis—the final stage of fetal development—and their manifestation is rarely the result of a single factor. Instead, these traits are influenced by a complex interaction between heredity and the environment.12

The reason for this dual influence is that gene expression is inherently modified by environmental conditions; no human attribute can exist or become actual without an environmental contribution. While some traits are strongly determined by genes, others are highly susceptible to external factors such as maternal nutrition, exposure to toxins, or physical constraints within the uterus.213

For example, while a child’s genetic makeup may predispose them to a certain growth pattern, environmental factors like adequate nutrition or the presence of teratogens can significantly alter the final outcome. Similarly, while some deformities are caused by intrinsic genetic issues, others result from extrinsic pressures, such as a lack of amniotic fluid failing to buffer the fetus from the uterine wall. Ultimately, the final physical form observed is the combined result of this nature-nurture interaction, making it difficult to isolate the separate contributions of each.324