User:Cpb45/sandbox

Evolutionary Considerations for Spontaneous Vertebral Fractures and Osteoporosis

Human primates have much weaker vertebral bone structure relative to body size than do other primates. This was determined through observation of bone size, density, porosity, and the ability of the ones to be compressed of the T8 vertebra (one of the most common vertebrae to demonstrate fractures in humans)1. The difference in bone structure relates to the prevalence of osteoporosis and osteoporosis related fractures in humans.

An ultimate cause to humans’ vulnerability to osteoporosis is due to the environment of evolutionary adaptedness (link) and the mismatch of evolutionary conditions to our modern environment. It has been proposed that our diets today may contain less than half of the nutrition that our ancestors ate during the evolution of our bone structure and the change to bipedalism2. This could be related to the low density of our bones and the vulnerability to fractures that we endure compared to other primates2.

Ape primates are seen to have stronger and more dense bone structure which may be why they exhibit fewer vertebral fractures than humans. While there are differences in structure, strength, and frequency of vertebral fractures, both humans and apes show signs of age-related bone loss1. The difference in frequency of fractures may be due to the more extensive bone loss that would need to occur in primates to make the bones as susceptible to breaking1. In addition, one very obvious difference between apes and humans is their mechanism for locomotion. Being bipedal is considered a great evolutionary advantage as it may allow for improved Darwinian fitness via available limbs for holding and gathering food along with child protection3,4. Being bipedal increases the amount of pressure on the two platforms that make contact with the ground compared to the distribution of pressure over four limbs in quadrupeds such as apes4. With this increase in pressure, the porous structure of the human bones may in fact help to disperse and absorb this pressure. In addition, being bipedal also changes where force occurs on the body. The vertical pressures exhibited on the spine in bipeds are not seen in quadrupeds4. The reason that osteoporosis or age-related bone loss have not been selected against evolutionarily is because they serve a greater purpose. They are the by-product of the advantages and modifications associated with bipedalism. Lastly, osteoporosis is a mechanism of time. In general, the injuries associated with osteoporosis do not occur until after the reproductive period of the individual and therefore do not affect the fitness of the organism1,4. Understanding the evolutionary causes to our loss of bone mass density and therefore osteoporosis and frequent age-related fractures can help us to appreciate the disease but also provides potential models of other animals and our evolutionary ancestors that may help to elucidate preventative strategies and treatments for the condition.

1.	Cotter, Meghan M., et al. "Human evolution and osteoporosis-related spinal fractures." PloS one 6.10 (2011): e26658.

2.	Eaton, S. Boyd, and Dorothy A. Nelson. "Calcium in evolutionary perspective."The American journal of clinical nutrition 54.1 (1991): 281S-287S.

3.	Preuschoft, Holger. "Mechanisms for the acquisition of habitual bipedality: are there biomechanical reasons for the acquisition of upright bipedal posture?."Journal of anatomy 204.5 (2004): 363-384.

4.	Latimer, Bruce. "Editorial: The Perils of Being Bipedal." Annals of biomedical engineering 33.1 (2005): 3-6.