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Hello everyone, SCIEN-SPOT is a podcast that shines a spotlight on the latest scientific technology from Japan.
Your host is REN from SCIEN-TALK.
傷の治癒の重要性
Now a quick question. When you get a cut or scrape your knee, you probably think,
I wish this would heal faster. We put on a band-aid, disinfect it, or maybe use some ointment,
and most of us probably just assume it will heal naturally over time.
But what if the speed at which our wounds heal is actually dramatically slower than that of many other animals on earth?
I'm talking about dogs, cats, even small mice, birds, and even our close genetic relatives, chimpanzees.
Today I want to talk about a fascinating study from University of Ryukyu in Japan that uncovered this surprising fact.
This discovery might just change how you think about your own body and what it means to be human.
Let's start with why healing is so important for any living creature.
When a body gets injured, that wound becomes an open door for pathogens, bacteria, and viruses to get inside.
This can lead to serious infections, and constant breathing can be life-threatening.
That's why almost every creature on earth has evolved an incredible self-repair ability, a healing power,
to close wounds as quickly as possible and return to its normal state.
Think about wild animals living in nature.
If a lion gets a cut while hunting or a zebra escapes its leg escaping a predator, what happens if that wound doesn't heal quickly?
They'll get weak from infection, they won't be able to run, and eventually, they'll either be caught by a predator or starve because they can't hunt.
For them, the ability to heal wounds is a lifeline directly connected to their survival.
Unlike humans, they can't just go to a hospital for treatment, so their self-healing ability directly determines their survival rate.
傷の治癒過程の理解
In biology, the wound healing process is incredibly complex and precise.
The moment a wound occurs, hemostasis begins to stop the bleeding, then the immune system rushes in to fight off germs and remove dead cells and foreign matter.
This is the implementation stage.
After that, new skin cells and blood vessels are created, filling in the wound from the inside.
This is the proliferation stage.
Finally, the skin reveals and the scar matures in a process called remodeling, completing the healing.
This entire sequence is remarkably coordinated with various cells and chemicals working together.
We usually don't think about it, but the grand drama is constantly unfolding beneath our skin to protect us.
About all this, the research team at the University of Ryukyu had a truly intriguing and for us, perhaps a bit shocking question.
Could it be that human wounds heal slower than those of other animals?
The spark for this question came from a simple realization in the lab.
A researcher noticed how incredibly fast the wounds on their laboratory baboons healed and wondered, why is this?
How is it different from humans?
This pure scientific curiosity led to groundbreaking discoveries that challenged our common understanding.
In this study, the researchers regularly computed the healing speed of wounds in human skin with those on the skin of other primates, like chimpanzees and even animal-like mice.
Healing speed wasn't just about how long it takes for the wound to close.
They tracked the detailed cellular movements, like how fast cells at the wound's edges multiplied and moved toward the center and how quickly new blood vessels formed.
The results were astonishing.
They discovered that human wounds heal approximately three times slower compared to other animals.
人間の傷の治癒速度
This means if a mouse's wound of the same size and depth heals in three days, it must take a human nine days.
It's like realizing your skin is taking its sweet time even more than you thought.
This finding was a big surprise in the scientific community because while many studies have looked at wound healing mechanisms,
a clear comparison of healing speeds between species, especially the fact that humans are so remarkably slow, had rarely been focused on before.
So why did humans alone evolve this seemingly disadvantageous trait of slower wound healing?
In the competitive world of nature, why would evolution sacrifice such a crucial healing ability?
The researchers have come up with some very compelling hypotheses.
This is the hypothesis 1, connection to upright walking.
One of the most likely possibilities is its connection to bipedalism, or walking upright on two legs, which humans adopted during evolution.
Like most other animals, humans can stand and walk fully upright on two feet.
This bipedalism gave us many benefits like a wider field of view and a free hand for using tools.
But as a trade-off, the skin on parts of our bodies, like our buttocks and the soles of our feet, became constantly subjected to bearing weight and friction from the ground.
And if the skin in these areas healed very quickly with actively multiplying cells, like in other animals, what might happen?
It could become excessively thick over a frequently developed heart, cells like growth, potentially impairing our delicate movements and sensations.
Also, excessive skin growth might make it lose its flexibility and elasticity, hindering efficient walking.
So, to maximize the benefits of bipedalism, a vital treat for survival, humans might have made an evolutionary choice to deliberately slow down the proliferation of skin cells, either in species alike or throughout the body.
傷の治癒メカニズムとその影響
This would prevent excessive skin thickening and maintain flexibility and sensation.
It's like a high-performance sports car designed to sacrifice absorbing mirror-rolled vibrations to achieve higher speeds.
The fact that the entire body's skin showed this slowness suggests that the genes and molecular mechanisms controlling skin cell proliferation come on throughout the body.
And now, Hypothesis 2, Longevity and Cancer Risk Reduction
Another very interesting hypothesis related to human longevity compared to other animals.
As I mentioned earlier, a rapid wound healing mechanism means cells are proliferating very actively.
When cells divide repeatedly, they always carry the risk of genetic copying errors or mutations.
If cells proliferate excessively and uncontrollably, these mutations can accumulate, potentially increasing the risk of cancer.
Humans have a much longer lifespan than chimpanzees, who live around 40 years on average, with modern humans often living over 80 years.
Over this long lifetime, our bodies undergo trillions of cell divisions.
To keep the risk of cancer low throughout this extended life, humans might have deliberately slowed down the rate of cell proliferation
and evolved a system to reduce copying errors or more strictly check and eliminate cells with mistakes.
This is like building a house carefree over time, ensuring a solid foundation for longevity.
Rather than rushing into the risky quick collapse, it's choosing safety and durability over speed.
These two hypotheses aren't mutually exclusive, it's quite possible they work together.
Human evolution is too complex to be explained by a single factor.
This research from the University of Ryukyu is incredibly significant not just for confirming that human bones heal slowly,
遅い治癒の進化的背景
but for delving into the evolutionary reasons behind it.
It's a crucial step in unraveling the mystery of this disadvantageous evolution
and understanding how we humans became who we are today.
The discovery has the potential to impact various fields, regenerative medicine or drug discovery, dermatology and cosmetic medicine,
new perspectives on evolutionary biology, and implications for cancer research.
Of course, this research is just the beginning.
By further exploring the detailed molecular mechanism and conducting more comparative studies across different species,
the mystery of slow human bone healing will likely be unravelled even further.
We can only hope that this will bring new answers to our health, medicine, and even the fundamental question of what it means to be human.
Okay, so that's all for today's SciencePod.
This podcast is broadcasted daily on weekday morning in both Japanese and English.
I'd love for you to listen to the podcast and post your notes and thoughts with the hashtag SciencePod.
See you next time.
