Bilateral symmetry

Bilateral symmetry is a fundamental concept in biology and anatomy that refers to the arrangement of an organism's body parts along a central axis, such that the organism can be divided into two identical halves. This type of symmetry is a common characteristic of many living organisms, including humans and most other animals.

Overview

Bilateral symmetry is one of several types of biological symmetry. It is contrasted with radial symmetry, where an organism's body parts are arranged around a central point, and asymmetry, where there is no pattern to the arrangement of an organism's body parts.

In organisms with bilateral symmetry, there is typically a clear distinction between the front (or anterior) and back (or posterior) of the organism, as well as the top (or dorsal) and bottom (or ventral). This allows for a high degree of specialization in different parts of the organism's body, which can be advantageous for survival and reproduction.

Evolution

The evolution of bilateral symmetry is thought to be a major evolutionary milestone. It is believed to have first appeared in the Ediacaran period, over 600 million years ago, and is a defining characteristic of the Bilateria, a group that includes the majority of animals, including humans.

Bilateral symmetry is thought to have evolved in response to the demands of locomotion and predation. It allows for streamlined movement and a concentrated sensory apparatus at the front of the organism, both of which are advantageous for hunting and escaping predators.

Implications for development and disease

Bilateral symmetry also has important implications for the development of organisms and the diseases that can affect them. For example, many genetic disorders and diseases can disrupt the normal bilateral symmetry of an organism's body, leading to a range of health problems.

See also

• Symmetry in biology
• Radial symmetry
• Asymmetry
• Bilateria
• Evolution of bilateral symmetry