Osteoporosis in humans but not gorillas due to additional life stage

Osteoporosis develops in humans but not in gorillas. Source: PublicDomainPictures (via Pixabay)
Study by Johns Hopkins researchers and collaborators shows a post-reproductive stage could be why osteoporosis develops in humans but not gorillas

By Mili Jayadeep | Science Editor

The medical condition osteoporosis is mainly associated with older women but can affect men and other age groups. Although bone loss is expected in the ageing process, accelerated bone loss causes weaker bones that can develop into osteoporosis. With the condition affecting about 3 million people in the UK, over 500,000 people require hospital treatment due to fractures caused by it. This condition induces the loss of bone mineral density and associated changes that increases its susceptibility to fracture. It mainly affects women particularly following menopause because of the hormonal changes occurring in the body. 

A recent study conducted by Johns Hopkins Medicine researchers and collaborators including the Rwanda Development Board, Gorilla Doctors and George Washington University researchers highlighted important findings. Their work showed that the presence of an additional post-reproductive life-stage could explain why humans develop osteoporosis while gorillas do not. The research conducted on gorilla skeletons from Rwanda’s Volcanoes National Park was published in the journal, Philosophical Transactions of the Royal Society B. The Professor at the Centre for Functional Anatomy and Evolution at Johns Hopkins University, Christopher Ruff, describes:

“In terms of natural selection, there is no evolutionary advantage in developing bone loss with aging to the point of a potential fracture. By looking at close relatives of humans on the evolutionary tree, we can infer more about the origins of this condition.”

The team performed analysis on 34 mountain gorilla skeletons with a similar number of male and female bones ranging from ages 11 to 43 years, which includes the full adult stage age-group in gorillas. The study used a specialised CT scanner to study bone mechanics such as bone density and geometry, both of which give clues into bone health. Ruff says:

“This detailed, long-term data on individual gorillas is critically important to this kind of anatomical research work. Extensive demographic information, including the age at death, allows investigations that are difficult or impossible to carry out in other wild primate populations.”

The observations showed similar indications of normal bone aging to that occurring in human bones. The bones showed an increased diameter of the long bones and weakening bone wall linked with greater bone age. However, there was no noticeable indication of bone mineral loss as seen in osteoporotic human bone. There were also no significant differences between the bone mineral density of older male and female gorillas. Whereas, in humans, older women have lowered bone mineral compared to older men. 

 The explanation to this phenomenon may lie behind the reproductive stage differences between humans and gorillas. Gorillas have offspring throughout the adult stages of their lives, which causes continued exposure to certain bone-protective hormones. Furthermore, humans have an additional life stage where reproduction can occur and then a post-menopausal stage where it cannot. This means that osteoporosis develops in humans but not gorillas.

Based on the evidence, the researchers theorise that the additional life stage unique to humans that arose after the evolutionary split between African apes and humans, may be responsible for diseases accompanying older age such as osteoporosis.

Science and Technology Mili Jayadeep

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