Is it possible to wake up and travel back to tens of thousands of years in the future? Ancient nematodes can do it

Produced by: Science Popularization China

Author: Qian Yu (PhD, Center for Excellence in Brain Science and Intelligence Technology, Chinese Academy of Sciences)

Producer: China Science Expo

Captain America in "The Avengers" fell into the frozen sea during an operation at the end of World War II. He was not thawed until 2011. For him, it may have been just a long dream, but the whole world has undergone earth-shaking changes in the past seventy years.

Captain America Frozen

(Photo source: Stills from Captain America)

So in real life, can we also freeze ourselves and wake up in the future?

Ancient nematodes can do it!

In 2018, scientists revived ancient nematodes that had been frozen in the Siberian permafrost for tens of thousands of years. At that time, their life was thought to have begun 42,000 years ago. In the latest work in 2023, scientists used precise radiocarbon detection technology to discover that these ancient nematodes had been in a "dead-awake" state in Siberia for at least 46,000 years ago, also known as "suspended death" or "cryptobiosis."

Nematodes from 46,000 years ago

(Image source: Reference [1])

In the cryptobiotic state, the metabolic capacity of life will be reduced to an undetectable level, which is equivalent to pressing the pause button on life. Common examples include: a Bacillus spore preserved in the abdomen of a bee for 25 to 40 million years, and a lotus seed preserved in an ancient lake from 1,000 to 1,500 years ago, they can continue to germinate and restart their suspended lives; metazoans such as water bears, rotifers and nematodes can also maintain a cryptobiotic state for a long time. Even if they are frozen for decades or even tens of thousands of years, as long as they are thawed and return to normal temperature, they can revive, eat, drink and reproduce normally.

Water bears "travel" after a meal of algae

(Image source: Megumu Tsujimoto)

Some higher animals, such as frogs, snakes, bears, etc., can hibernate and maintain a low metabolic level for basically only one winter. There is a kind of North American wood frog living in Alaska, which hibernates for nearly 8 months every year and can still survive after being thawed after being frozen for two months at -4℃.

So, can humans also be frozen for tens of thousands of years and then thawed and revived like nematodes? Unfortunately, this is not realistic at present.

Why can't humans do it?

If you were naughty as a child and accidentally put carbonated drinks such as beer and cola into the quick-freezing layer, you should know that it is easy for the bottle to burst when the water turns into ice (friendly reminder: this operation is very dangerous, please do not do this).

Beer bottle burst by frozen beer

(Photo source: veer photo gallery)

Humans are made up of cells. In low-temperature environments, ice crystals formed by freezing of water in intracellular fluid can directly damage our cells, just like these beer bottles being pierced and shattered by ice crystals. At the same time, as water molecules slowly arrange into an orderly crystal structure, they will also exclude the precipitation of sodium salts, potassium salts, calcium salts, etc. that are originally soluble in water. High concentrations of salt can also cause dehydration damage to cells and even death.

The water bear mentioned above can curl up into a barrel shape and reduce the water content of the body to only 3%. After being completely dehydrated, it can become a "zombie worm" with almost stopped metabolism. At the same time, it uses trehalose produced by the body to replace the water in the body, thus preventing the body fluid from forming ice crystals to damage its own cells. The Alaskan wood frog changes the concentration of its body fluid through urea and glucose in the body, effectively lowering the freezing point of the body fluid, which can greatly reduce the content of frozen water and avoid damage to cells.

Trehalose, urea and glucose mentioned above, which prevent ice crystals from appearing and damaging cells, can all be called "cryoprotectants." Therefore, the first step of artificial freezing is usually to reduce the water content of the frozen organism as much as possible and inject cryoprotectants with complex ingredients such as glycerol, so as to maximize the survival rate of cells after the organism wakes up.

Dried fruits made by sun drying or drying can increase the shelf life

(Photo source: veer photo gallery)

There are many vertebrates that can be revived from natural freezing, such as frogs, snakes, salamanders, turtles, etc., which are all cold-blooded and temperature-changing animals. Unfortunately, humans are warm-blooded animals that will have problems if their body temperature drops. They cannot dehydrate as quickly as these animals, or naturally adjust the concentration of "cryoprotectants" in their bodies, so they cannot reduce their metabolic capacity to the minimum.

Even if the survival rate of cells after freezing and thawing is as high as 99%, for a human brain with nearly 86 billion neurons, 860 million neurons will die, which may affect the normal function of the brain's delicate operation. If only the brain related to consciousness is preserved, then it doesn't matter whether the body is carbon-based or silicon-based composed of machinery. "I" is still "I", just like Yun Tianming in The Three-Body Problem. Even if the body disappears completely, as long as the brain is there, it can still think.

How far has brain cryopreservation technology advanced?

A frozen hamster brain can still be awakened if it is 60% crystallized.

In 2015, the 21st Century Medical Laboratory, funded by the American Brain Protection Foundation, performed a complete aldehyde-stabilized cryopreservation surgery on rabbits. The specific operation was: glutaraldehyde was perfused into the carotid artery of the living rabbit to fix the rabbit brain, and then ethylene glycol was slowly perfused with increasing concentrations over several hours, and finally frozen at -135°C. After the frozen brain was reheated and thawed, the researchers observed from the brain slices that the brain structure was very well preserved, the synapses were also clear, and the nerve cells were basically undamaged.

Rabbit brain successfully preserved and revived with no cell damage

(Image source: Reference [7])

The rabbit brain is fine, but what about the human brain?

In May 2024, researchers from Fudan University in my country successfully established a method for cryopreserving various brain organoids or human brain tissues using methylcellulose, ethylene glycol, dimethyl sulfoxide and Y27632 selective inhibitor (this method is called MEDY) without destroying the structure of nerve cells or affecting functional activities.

This method can protect synaptic function and inhibit the endoplasmic reticulum-mediated apoptosis pathway, thereby reliably storing a variety of neural organoids and living brain tissue on a large scale. This method can "freeze" the human brain for 18 months and then safely remove it, which is already a significant progress.

Schematic diagram of MEDY brain organ cryopreservation technology

(Image source: Reference [8])

How long will it take to achieve the “freeze-thaw” resurrection of the human body?

In April 1967, Professor James Bedford, a psychology professor at the University of California, died of advanced kidney cancer. He decided to cryogenically store his body, hoping for future medical developments.

After his death, his body was hastily placed in a special metal container filled with -196℃ liquid nitrogen. The entire freezing operation lacked mature technology and professional support. So in June 2024, after Professor Bedford's body was thawed, scientists found that his brain and body were severely damaged and his life could no longer be restarted. After more than 50 years of waiting in the cryostat, the professor did not successfully come back to life, but this brought very precious thawing data.

The first "frozen person"

(Image source: Cryonics)

Currently, the United States has two largest human cryonics companies, one is the Alcor Life Extension Foundation, and the other is the American Cryonics Research Institute. Currently, there are hundreds of people in the world who have frozen their dead bodies in the hope of "resurrecting" in the future, but there are still no successful cases of thawing and resurrection. The vast majority of frozen people were already elderly before they died, and some suffered from terminal illnesses and serious diseases. Their poor personal conditions often further reduce the success rate of "thawing".

Based on the desire for perfect resurrection, cryopreservation technology for human organs and excellent animal and plant germplasm resources is developing rapidly. Perhaps one day in the future, we only need to preserve and thaw the brain, and then combine it with a machine to "revive". This will not only reduce the technical requirements for freezing and thawing, but also get rid of the old, fragile or sick carbon-based body.

Assuming that human body preservation technology is successfully applied, everyone will have the opportunity to enter a freezer for hibernation and face the future tens of thousands of years later after resuscitation. Then, who should be preserved to continue life and face the future? Will people in the future welcome a person from the past whose ideas and skills are outdated? If the company that takes care of the frozen people goes bankrupt, who will be responsible for the "life safety" of these "corpses"?

There is still a long way to go in terms of technology, ethics and law to achieve the "freeze-thaw" resurrection of the human body.

References

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permafrost shares adaptive mechanisms for cryptobiotic survival with C. elegans dauer larva. PLoS Genet, 2023, 19(7): e1010798.

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[3] Cano R, Borucki M. Revival and identification of bacterial spores in 25- to 40-million-year-old Dominican amber. Science. 1995; 268: 1060–1064.

[4] Shen-Miller J. Sacred lotus, the long-living fruits of China Antique. Seed Sci Res. 2002; 12: 131–143.

[5] Guidetti R, Jo¨nsson KI. Long-term anhydrobiotic survival in semi-terrestrial micrometazoans. J Zool. 2002; 257: 181–187.

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neural organoids. 2024, Cell Reports Methods 4, 100777