The Biology of Why Chimps Are Stronger than Humans Explained

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For over a century, the idea of chimpanzees being incredibly strong has fascinated both scientists and the public. Early research suggested these primates could be up to five times stronger than humans, and even the most conservative estimates doubled their strength compared to ours.

But more recent research in the Proceedings of the National Academy of Sciences (PNAS) is challenging these long-held beliefs, revealing that while chimpanzees are indeed stronger, the difference is not as extreme as once thought.

Photo byO'Neill et al., PNAS.

The Real Source of Chimpanzee Strength

Contrary to popular belief, the secret behind chimpanzee strength isn't stronger muscle fibers but rather the specific ratio of different muscle tissues.

This discovery provides fresh insights into how human and chimpanzee muscles have evolved to suit our distinct lifestyles. The PNAS research highlights that chimpanzee muscles are about 1.5 times stronger than human muscles, primarily due to a higher proportion of fast-twitch muscle fibers.

Specifically, researchers from the University of Massachusetts took a comprehensive look at studies conducted between 1923 and 2014. Their analysis suggests that previous strength estimates were inflated due to a lack of consideration for factors like muscle arrangement and body shape.

By isolating muscle fibers and testing their force, contraction speed, and myosin distribution, the team found that chimpanzee muscles are not fundamentally different from human muscles, but they are organized differently.

Fast-Twitch vs. Slow-Twitch Muscle Fibers

Muscle fibers come in two primary types:

• Slow-twitch fibers are designed for endurance, allowing muscles to sustain activity over long periods.
• Fast-twitch fibers, on the other hand, provide short bursts of power but fatigue quickly.

The study revealed that chimpanzees possess nearly twice as many fast-twitch fibers as humans, which accounts for their greater strength. This difference gives chimps the powerful, quick movements needed for their arboreal lifestyle.

Evolutionary Trade-Offs

The study's findings also shed light on the evolutionary trade-offs between strength and endurance.

As humans evolved to cover long distances on foot, our muscles adapted by increasing the proportion of slow-twitch fibers, which are more suited to endurance activities. Meanwhile, chimpanzees retained a higher proportion of fast-twitch fibers, which are advantageous for climbing and swinging through trees.

As one of the research authors said:

"We found that within fibre types, chimp and human muscle fibres were actually very similar. However, we also found that chimps have about twice as many fast-twitch fibres as humans."

"When we compared chimps and humans to muscle fibre type data for other species we found that humans are the outlier, suggesting that selection for long distance, over-ground travel may have been important early in the evolution of our musculoskeletal system.

Conclusion

This research offers a new perspective on chimpanzee strength, revealing that while they are indeed stronger than humans, the difference is more moderate than previously thought.

The study highlights the importance of muscle fiber composition in determining strength and provides valuable insights into the evolutionary paths that humans and chimpanzees have taken.