Bilateral Symmetry in Embryos and Supermodels

Bilateral symmetry is a type of body plan in which an organism has two mirror-image halves along a single axis. The axis of symmetry is the sagittal plane, which passes vertically through the head and body. Each half has one set of sensory organs and appendages: one eye, one ear, one arm and one leg. The symmetry is not perfect, but it is approximate. This symmetry is also present at the cellular level, as most cells have a polarized structure. Bilateral symmetry is a common feature of most animals, including humans. The earliest evidence of bilateral symmetry is Vernanimalcula, a microscopic animal from the Ediacaran period.

Facial symmetry is a measure of how similar the left and right sides of a human face are. It is often associated with attractiveness and health. It may also be related to some mathematical patterns such as the Fibonacci sequence or the golden ratio. The reason for this link is that facial symmetry reflects the quality of embryonic development.

The philtrum is the vertical groove between the nose and the upper lip. It is formed by the fusion of two embryonic structures: the medial nasal prominence and the maxillary prominence. This fusion occurs during the fourth week of gestation, and it is influenced by genetic and environmental factors. A symmetrical philtrum indicates a successful fusion and a normal development. A failure of fusion or asymmetry may indicate a range of congenital anomalies or disorders. In evolutionary terms, facial symmetry can be a reliable indicator of fitness and health. Evolution can be as selective as a supermodel, and as elegant as symmetry.