What is life?

Bernard,

I think that the following, from this recent eSkeptic discussion, is not completely correct: “…reproduction is an absolutely essential component of any definition of life.” By this measure almost every instance of a living, breathing female mule and her male mule consort are not alive, since they cannot reproduce. From Wikipedia: “Mules and hinnies have 63 chromosomes, a mixture of the horse’s 64 and the donkey’s 62. The different structure and number usually prevents the chromosomes from pairing up properly and creating successful embryos, rendering most mules infertile. … As of October 2002, there had been only 60 documented cases of mules birthing foals since 1527.”

Is a frozen cell alive? Is any cell anywhere alive? The answer must be “no” when the cell is considered independent of its surroundings. A cell lives only in the context of an environment necessary to its continued energy-transfer function. A necessary but not sufficient property of being alive is metabolizing, i.e. having energy flowing through during short periods of time.

Are Henrietta Lacks’s HeLa cells alive? Only artificially. But does that matter in the definition? The HeLa cells reproduce by division, but their genome never changes. Or does it? Are HeLa cells alive only as long as subatomic particles haven’t yet punched enough holes in their genome to disable proper division? It must be that HeLa is not immortal, instead only stable so much longer than we’re accustomed to that they seem immortal to our very mortal eyes.

One could conclude that the only truly alive things are species in their native habitats. But all animal species are just big, self-assembling buses for bacteria; take away the environment that fuels the bacteria and the species will quickly disappear. So animals are not alive except insofar as their bacterial needs are being fulfilled. Plants might be able to live without bacteria – I don’t know, do you? The net seems to be, our planet is alive to the extent it continues to receive more or less the same sunshine as we experience today and to spin as it does today, etc. Any smaller unit than the whole planet in its current context perishes quickly and might as well be considered dead as soon as its energy environment moves permanently outside certain boundaries, for example the intensity of sunlight impinging.

The Dalai Lama says in How To See Yourself As You Really Are: “… when the idea that objects inherently exist takes hold, fundamental ignorance has been introduced.” Nothing exists in and of itself; all things are interconnected; remove an essential connection from a thing and it perishes; among the most fragile things are the living ones.

Wayne

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Wayne,

The meaning or definition of life is a difficult problem of modern biology. I’m not an expert on this, but that has never stopped me from pontificating on any other subject.

Here’s a description of life’s characteristics from Wikipedia:

Life is considered a characteristic of something that exhibits all or most of the following traits:

Homeostasis: Regulation of the internal environment to maintain a constant state; for example, sweating to reduce temperature.

Organization: Being structurally composed of one or more cells — the basic units of life.

Metabolism: Transformation of energy by converting chemicals and energy into cellular components (anabolism) and decomposing organic matter (catabolism). Living things require energy to maintain internal organization (homeostasis) and to produce the other phenomena associated with life.

Growth: Maintenance of a higher rate of anabolism than catabolism. A growing organism increases in size in all of its parts, rather than simply accumulating matter.

Adaptation: The ability to change over time in response to the environment. This ability is fundamental to the process of evolution  and is determined by the organism’s heredity, diet, and external factors.

Response to stimuli: A response can take many forms, from the contraction of a unicellular organism to external chemicals, to complex reactions involving all the senses of multicellular organisms. A response is often expressed by motion; for example, the leaves of a plant turning toward the sun (phototropism) , and chemotaxis.

Reproduction: The ability to produce new individual organisms, either asexually from a single parent organism, or sexually from two parent organisms, “with an error rate below the sustainability threshold.”

These complex processes, called physiological functions, have underlying physical and chemical bases, as well as signaling and control mechanisms that are essential to maintaining life.

There is “reproduction” as an important element. I think that this list would be typical of what we’d find if we were to look in any modern biology text of any level. Notice that it says life contains “all of most” of these. The biologists recognize that there are interesting borderline cases. Thus, what about viruses?

Your example of a mule is a good one. Of course, the mule’s individual cells, we’d say, meet the definition of life, even though at any particular moment, most of them are not reproducing. So the mule as a complete entity can’t meet the criteria of reproduction, but it meets the other criteria.

Of course, you are correct that if you remove a living organism from its environment, the flow of energy and food, then it will fail homeostasis, metabolism, growth, adaptation, and evolution. By this point, I’d say it hasn’t met the “all or most” condition of the definition.

The HeLa cells are alive, I’d say, although any particular one of them might die. I wouldn’t say that the HeLa cells, taken as a whole, form an organism, however. But each cell is an organism, no different than any other single cell organism such as algae. So cultured single cells may fit the definition without difficulty. But they are not Helen Lacks, who is not alive, even though some of the descendants of her cells are still living.

For readers who don’t follow the link to the eSkeptic item, I’ll say that it is a discussion between two professors about life, and whether naturalism is sufficient to explain it or is the supernatural is necessary. One matter they discuss is whether a frozen cell is alive, since it appears to meet or to be able to perform all the requirements of life, but it just happens not to be doing so. Indeed, some organisms can survive and revive after being frozen. I guess that I agree with the professor who says that when the cell is frozen, it is not alive, but when it has been revived, it is alive. The other fellow says that it is alive frozen or not.

Even though it has been a theme of modern Western scientific discovery since Newton put forward his theory of universal gravitation that certain (simple to some people) laws or regularities govern all of nature, I’m not a supporter of mystical pronouncements such as that of the Dalai Lama. But I wouldn’t argue with him about it. It’s OK by me.

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Bernard,

To me the Dalai Lama is not mystical, not a bit of it! He means what he says literally, and I take it as so.

Consider: You cannot remain alive for more than a few weeks unless you can  ingest enough digestible material and enough water, and remain sheltered from the full blast of the sun’s radiation, yet not so sheltered that you freeze. Where does your digestible material come from? Ultimately it all comes from other life. Only the lowest level cells on the planet get sustenance from non-organic sources together with heat from sunlight or from the earth’s internal structure. You depend entirely on other life to be able to live. The lowest-level cells depend on available heat and appropriate chemistry.

Now consider the molecules in the substances you consume, and the atoms in the molecules. A universe consisting of a single atom is inconceivable (so far anyway). Even if it existed nothing could or would happen in it. All objects in our known universe depend on other objects to help collectively maintain overall structures within which and among which stuff can happen. Take away enough of a crystal, or a portion of a crystal, and it’s no longer crystalline. Take away the sun and the earth spins off into oblivion, probably sucked into a black hole eventually.

No object lives alone. All depend on other objects. Is this not literally true? Do you still assert that the Dalai Lama speaks only mystically?

Wayne

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Filed under Biology, Life, Natural Science

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