This incredible animal has survived all 5 extinctions on Earth. | Image: Archive
From the moment in which Darwin (like Wallace) discovered natural selection and its implications for the evolution of species, human beings have been fascinated by how, through this ancient process, animals adapt to the environment and develop incredibly sophisticated mechanisms .
But there comes a day when you discover an animal, with amazing abilities that far exceed everything you thought you knew and predicted about the qualities of animals. This day is today, thanks to the tardigrades or water bears. Being in all probability the most resistant animal in the world,able to survive in the vacuum of outer space, this tiny being will surprise you .

What is a tardigrade?
These beings are also known as water bears, due to the way they move and their appearance. They are invertebrates, oviparous , they are segmented like a silkworm and have an average size of half a millimeter long (which means that they can be seen with the naked eye), although the smallest can measure 10 times less.
Likewise, they are terrestrial animals that generally live on the surface of the water that covers mosses, ferns and lichens. Despite their preferences, they can inhabit both freshwater and saltwater, being able to survive practically anywhere .of the world.
These animals were discovered by Johann August Ephraim in the year 1773, who gave them the name of Water Bear (although the original translation from German is “water bears”). The name of Tardigrado was given to him 4 years later by Lazzaro Spallanzani and means “slow step”.

What capacities and particularities do they possess
Without a doubt, this living being stands out for being almost indestructible since it is considered to be capable of surviving in extreme conditions. There are already numerous studies that have tested tardigrades with almost unbelievable results. Here are some examples:
A study published in the journal Nature by Kunihiro Seki and Masato Toyoshima showed that tardigrades werecapable of surviving under pressures of 6000 atmospheres of pressure . Let us remember that the natural pressure that we find ourselves in right now is equal to 1.
Regarding the famous and incredible ability to survive in space, it is something that the Italian Space Agency verified in the Biokis Project. This project with different missions consists of sending microorganisms into space to study them. Well, they carried out a mission with water bears, where they found that they were capable of surviving in the vacuum of space for up to 10 days .
In terms of temperatures, of course, they are also specialists in resistance, because of course, it is very cold in space, so it was to be expected that they would also be resistant to thermal levels. In fact, such is their resistance that they withstand temperatures ranging between -200ºC and 150ºC . In other words, they withstand space cold and the temperature at which water boils.
Dehydration is not a problem for our friends either. As we well know, living beings are dependent on water to function, to a greater or lesser extent. Well, water bears are able to enter a state of hibernation when they suffer from dehydration. Of course, we are not talking about normal weather like a polar bear hibernating in winter, but aboutperiods of up to 10 years without obtaining water .
As if that were not enough, some tardigrades have learned to lay their eggs while they shed their skin (cuticle), in such a way that it serves as protection for the eggs and future offspring.

Why are they so resistant?
The fundamental mechanism that allows them to remain in a state of hyper-resistance in the face of all these inclemencies is known as cryptobiosis or anhydrobiotic state . It is a complex system that is still being studied today, but its basic principle is to dehydrate the animal’s body.
This dehydration makes the body of the tardigrade go from the usual 85% of body water to an incredible 3%. As expected, this state prevents the water bear from reproducing or growing, since it reduces the metabolism to a rate of 0.01%.
Although under natural conditions the tardigrade can spend between 4 and 10 years in this state of cryptobiosis, a group of researchers from the National Institute of Polar Research of Japan (NIPR) managed in 2016 to revive specimens of this species that had been frozen for 30 years .
In short, anhydrobiosis is a state with different factors working together as bioprotectors of the tardigrade. Morphological, physiological and biochemical variables come into play to allow this state to last and protect it for years.

are you exaggerating
Well, at this point, we must ask ourselves to what extent tardigrades are or are not the most resistant animal in the world. The truth is that they are, since compared to cockroaches, these look like fragile seahorses. However, even if they have well deserved the title, you have to have a critical spirit .
First of all, it is not entirely correct to say that water bears can live without water, at -200ºC or in space. Rather, they enter a kind of temporary standby until conditions improve. But during that period, they do absolutely nothing. This, translated in other words, means that if the conditions do not change, the tardigrade will die sooner or later (although a decade must pass).
In fact, the state of hibernation is so extreme that to say that they are alive is a pretty risky label. Rather we could say that they are potentially alive . As if it were a computer turned off; we cannot say that it is on, rather that it can be turned on again.
Subsequent studies, for example, have found that the ability of tardigrades to incorporate genes from other species is not as high as previously thought. In fact, it was initially said that 17% of the genes of these beings are stolen from other species. But a recent study by the University of Edinburgh and Keio University has reduced that figure to 0.7% .