Most people have five vertebrae in their lumbar (lower back) region, which are named L1 to L5. However, some people possess an additional lumbar vertebra located below the L5. This extra vertebra, known as the L6, is called a transitional vertebra. About 10 percent of adults have some form of spinal abnormality caused by genetics, and a sixth lumbar vertebra is among the most common of these abnormalities.
Question- What is the current explanation to why some humans have developed this extra vertebra in the spine?