Scientists identify genes that gave us the power to walk on two legs

You walk on two legs not because you have two legs, it's because there are specific genes that have been working for thousands of years to make your bones suitable for bipedal locomotion.
Rupendra Brahambhatt
Representational image
Representational image

Pict Rider/iStock 

Do you know seven million years ago, humans also used to walk using four limbs? However, today, unlike most other organisms, we can stand straight on two legs and walk upright, but what gives us the ability to do so?

What makes our bones suitable to run bipedally? Surprisingly, even scientists didn’t know the answer to this simple question until recently, when researchers from the University of Texas (UT) at Austin and the New York Genome Center published a study that for the first time revealed the genes that design our skeleton.

The researchers used an AI program to study the genetic sequence of over 30,000 individuals along with more than 39,000 X-ray images of their different body parts. This analysis allowed them to identify genes that have been regulating the shape and symmetry of the human skeleton for thousands of years.

They claim their findings will enable doctors to predict the risk of bone-related disorders (like arthritis, lumbago, hip pain, etc.) in patients way before these conditions start developing in their bodies.  

“These disorders develop from biomechanical stresses on the joints over a lifetime. Skeletal proportions affect everything from our gait to how we sit, and it makes sense that they are risk factors in these disorders,” said Eucharist Kun, lead study author and a graduate research assistant at UT Austin.

Bipedalism and bone disorders

According to the Australian Museum, the human species learned to walk on two legs about five million years ago but back then it couldn’t run or jump or balance like we do. 

Such actions still required them to use all their limbs, and it took them another 3.2 million years to develop the perfect bone structure to achieve true bipedalism. The ability to walk upright on two legs has its many advantages, for example; it makes our body more energy efficient, highly maneuverable, and suitable for traveling long distances.

It also encouraged us to be creative with our remaining two limbs (hands), and that’s how we learned to move and manipulate objects, make tools, and carry goods. All this learning has contributed to increasing our intelligence.  

However, the skeletal changes that made us bipedal, also made us susceptible to musculoskeletal ailments like back pain and arthritis. Plus, with aging, it also becomes hard to maintain our body posture and balance. 

Being aware of these downsides of bipedalism, the researchers decided to look for the genetic changes that actually drive the changes in the human skeleton. They first went through the fossil record of many ancient human species to understand genetic factors contributing to changes in their skeleton proportions.

Then they examined the genome and X-rays of thousands of modern humans. With the help of an AI program, they processed and compared all this data and finally, identified 145 locations in the human genome that played a role in shaping human skeletons.

These genetic factors control the symmetry of each and every bone that you can find in your body from head to toe.

“On a more practical level, we’ve also identified genetic variants and skeletal features that are associated with hip, knee, and back arthritis, the leading causes of adult disability in the United States,” Tarjinder Singh, one of the study authors and an associate member of the New York Genome Center told The Independent.

The researchers believe that in addition to helping us predict the onset of skeletal disorders, the findings of this research work will also improve our understanding of human evolution as well as the divergence it brought in our bone structure.

The study is published in the journal Science.

Study abstract:

The human skeletal form underlies bipedalism, but the genetic basis of skeletal proportions (SPs) is not well characterized. We applied deep-learning models to 31,221 x-rays from the UK Biobank to extract a comprehensive set of SPs, which were associated with 145 independent loci genome-wide. Structural equation modeling suggested that limb proportions exhibited strong genetic sharing but were independent of width and torso proportions. Polygenic score analysis identified specific associations between osteoarthritis and hip and knee SPs. In contrast to other traits, SP loci were enriched in human accelerated regions and in regulatory elements of genes that are differentially expressed between humans and great apes. Combined, our work identifies specific genetic variants that affect the skeletal form and ties a major evolutionary facet of human anatomical change to pathogenesis.

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