Life #2 - Weirdness Everywhere

The lack of a definition to a term, as we know all too well, is a problem when dealing with governments. NASA, for example, wanted to search for life in space. For that, it needed a definition of life, writes Carl Zimmer in Life’s Edge. NASA came up with this:

“Life is a self-sustained chemical system capable of undergoing Darwinian evolution.”

That sounds right, even if a bit heavy on technical language.

 

But… the well-known exception is the good old virus. It doesn’t eat. It doesn’t grow in size. It doesn’t even reproduce – instead, it hijacks a living organism’s cellular machinery to make copies of itself. Viruses then are a headache for definition seekers. They have some characteristics, while lacking others.

 

Think of the good old RBC’s – red blood cells. They transport oxygen through the body. As anyone at a blood bank will tell you, blood has a life span of storage.

“If something has a life span, surely it has a life.”

And yet, be many definitions, RBC’s aren’t alive. They don’t have any DNA in them, for example. (Since they don’t have the “recipe” to make copies of themselves, the bone marrow produces them to replenish the ones that die). Remember the mitochondria, that thing inside our cells that produces energy? Well, RBC’s don’t have them either.

 

The mitochondria itself is weird. 2 billion years ago, it was a free-living bacteria. Then it merged with a larger cell. The mitochondria, from here on, would produce energy, while the cell would provide shelter. The mitochondria has lost most of its genes now – after all, it the cell is doing most things, the mitochondria doesn’t need genes for those things. So the mitochondria cannot build proteins, they cannot exist outside of cells. Yet, when a cell divides, the mitochondria makes a copy of itself. What would you call such a thing – alive or not?

 

If you thought DNA was a must-have characteristic of life, at least on earth, think again. Many viruses, including the famous COVID virus, have their code in RNA, not DNA. Why? Remember how the chain works – DNA to RNA to protein creation. If the ultimate purpose of life is to create proteins, then:

“(RNA viruses’) genes get translated straight to proteins.”

Skip the DNA, so much more efficient, the RNA based virus seems to say.

 

At this point, you are thinking the exceptions lie at the microscopic end of the spectrum. Wrong. As Szent-Gyorgyi pointed out, “thinking too categorically about those hallmarks (of life) was a one-way ticket to absurdity”! Take self-production –that’s a necessary characteristic of life, right? Yet:

“One rabbit can never reproduce itself. And if life is characterized by self-production, one rabbit cannot be called alive at all.”

 

Does that paradox suggest, he asked, that different features of life occur at different scales. Is self-production, by that logic, a characteristic at cellular level, not organism level?

 

Aha, you say, perhaps the point is that members of the same species mate to reproduce. First, we know the exception to that – donkeys and horses can mate to produce the sterile mule. But wait, there’s even more weird stuff out there. In the 1920’s, a naturalist couple stumbled upon a fish species in Mexico – it had only females, no males. They called it the Amazon molly, after those female warrior-only tribes. This species started when two different species, Atlantic mollies and sailfin mollies bred to produce the Amazon guppy. But if the Amazon guppy is all female, can it breed? Yes, in an unbelievable way. It always sticks with one of the parent species, Atlantic mollies or sailfin mollies. Why? To find a male to breed with. The male sperm (of the parent species) fertilizes the Amazon molly’s egg. And then the enzymes in the egg shred the would-be father’s DNA. Only the female Amazon molly’s DNA remains in the fertilized egg. Which then hatches into a new Amazon molly.

“The fish are sexual parasites, depending on other species for their reproduction.”

 

In 1972, Szent-Gyorgyi summed up his experience brilliantly:

“I moved from anatomy to the study of tissues, then to electron microscopy and chemistry, and finally to quantum mechanics. The downward journey through the scale of dimensions has its irony, for in my search for the secret of life, I ended up with atoms and electrons, which have no life at all. Somehow, along the line, life has run through my fingers.”