If sperm is live how can you freeze it temporarily for over 10 years?

Question

If sperm is live how can you freeze it using liquid nitrogen and cryogenics and then bring it back to life 10 years later? What happens to the 'life' part of the sperm during this period. Is it frozen in a state of slumber and what causes it it reappear upon defreezing?

Answer 1

It might be best to answer this by looking at a different question: why is it that cold kills things?

This isn't necessarily as easy question... I mean, we know that it DOES, but have spent decades figuring out exactly WHY. One problem that arises is that your cells do a lot of chemical reactions to operate, from 'burning' sugar to assembling nutrients into new cells and the like. And chemical reactions can depend a lot on temperature. So if you're not at the right temperature, those reactions can't go correctly. So being colder than you're supposed to is kind of like holding your breath on a cellular level - you can't get the things you need to stay alive done.

On the other hand, though, we all know that if we put something in the refridgerator it lasts longer. Cold affects not only human beings, but also the plants, fungi, and bacteria that might go after us as well as any other chemical reaction that might cause us to break down. So although we have trouble staying alive, we also have trouble dying.

A dramatic demonstration of this happens from time to time. There have been people fished out of rivers after an HOUR and completely revived (link 1). Normally a person would be drowned and dead within a few minutes, but if the water is cold enough, their need for air goes down too. They won't stay alive, but they don't die as easily.

Though we can't take advantage of this for whole people yet (when you try to freeze them, the inside stays too warm and can still die off) we can use this effect on simpler samples of tissue like blood, sperm, and the like. For sperm it is especially easy because they are very small and efficient to begin with - there isn't a lot of extra stuff that might get damaged. Blood can usually be frozen for about 40 days before it starts to go beyond reviving, but sperm might last thousands of years (link 2).

And who knows? Once medicine improves a bit, we might be able to freeze whole people for thousands of years too. We've been freezing whole hamsters and bringing them back since the 1950's, and many other creatures since them. We'll just have to see!