I’ve been studying the human body for over 25 years and one thing that escaped me at the beginning of that journey (mainly because it never seemed to be focused on) was the fact that there is so much human variation in our anatomy and physiology! We often hear phrases like “each body is unique” but what do we really mean by this?

Here are 5 ways that our anatomy and physiology can differ from someone sat next to us in a yoga class:

1)    The total number of bones in the human body can vary!

While many anatomy textbooks mention that there are 206 bones in the adult human body what is not always so apparent is that there is a range of possibilities here. 

Each of our feet are comprised of an average of 27 bones. The exact number can vary mainly due to presence or absence of sesamoid bones, which are small osseous elements that have formed within some tendons where they wrap around bony prominences.

While the lumbar spine is typically comprised of 5 vertebrae, the number of vertebrae can vary from person to person! A study by Hanson et al (2010) reported that 20% of patients did not have five lumbar vertebrae: 14.5% had six; 5.3% had four; one (0.13%) had the rare finding of three lumbar vertebrae!

There are typically 12 thoracic vertebrae however there is human variation here yet again. According to Glass et al (2002) approximately 5% to 8% of people lack a pair of ribs and subsequent thoracic vertebra. In a study by Yan et al (2018) 6% of the cohort had 11 thoracic vertebrae.

2)    Each of our joints are completely unique to us – just like our fingerprint! 

Probably the best example of this is the hip joint. The image below, courtesy of Paul Grilley beautifully demonstrates this huge variation in the position of the head of the femur relative to the shaft of the femur between individuals.

The femur on the left might make it reasonably easy for that student to sit in Lotus Pose while the femur on the right might make it really difficult for that student to even sit crossed-legged. Lotus Pose might be physically impossible for that student no matter how much they practise. As mentioned above, for the same individual there can be a huge difference in the architecture of their right and left femur.

3)    The number of muscles in the human body can vary also! 

The pyramidalis is a small, paired, and triangular muscle, anterior to the rectus abdominis. It is absent in about 20% of people. Psoas minor is also absent in a large percentage of the population (Farias et al 2012). Some people have an additional 5th head to their quadriceps femoris (Sam et al 2021).

4)    A rare number of people have their organs on the other side!

Situs inversus occurs when the organs in your chest and belly develop in a reversed position of normal anatomy.  

5)    Our physiology is also unique to each of us too!

Most people can perceive smell while some people cannot. Some people may be able to detect taste of certain materials like bitter leaf, while others cannot. Similarly, some can detect high, moderate and low salt concentration in cooked meal while others cannot. 

Few people can roll their tongues. There are no in-between or intermediates here. (Check out Daniel Radcliffe’s party trick below!)

Every human possesses one of the four blood groups called A, B, AB and O.

We each behave or react to certain things and conditions in our environment in different ways!

References:

Farias, M., Oliveira, B., Rocha, T. and Caiaffo, V. (2012) ‘Morphological and morphometric analysis of Psoas Minor Muscle in cadavers.’ J. Morphol. Sci 29, 4, 202-205.

Glass, R., Norton, K., Mitre, S. and Kang, E. (2002) ‘Pediatric ribs: a spectrum of abnormalities.’ Radiographics 22, 1, 87–104.

Hanson, E., Mishra, R., Chang, D., Perkins, T. et al. (2010) ‘Sagittal whole-spine magnetic resonance imaging in 750 consecutive outpatients: Accurate determination of the number of lumbar vertebral bodies - Clinical article. Journal of neurosurgery.’ Spine 12, 47-55.

Sam, F., Kandagaddala, M., Prithishkumar, I.J. et al. Prevalence of the additional head of quadriceps femoris in the South Indian population: a cadaveric and radiological study. Sci Rep 11, 16132 (2021).

Yan, Y., Li, Q., Wu, C., Pan, X. et al. (2018) ‘Rate of presence of 11 thoracic vertebrae and 6 lumbar vertebrae in asymptomatic Chinese adult volunteers.’ J Orthop Surg Res 13, 124.