OK, last post about this, I kinda promise.  I was thinking about this and reading Luisi's book and he asked another interesting question... one that reflects part of the discussion yesterday.  If you survive all the way to the end, then you will be rewarded with my favorite (and only) Halloween joke... just to show I can do stuff besides ask pointless question.

Let's put aside the question about the difference between an apple and its tree and whether a dead thing has live cells and get to the fundamentals.

Take the nucleus out of an oocyte, as in the cloning experiments, is the nucleus living? And is the cell, without a nucleus, alive?

Now we get even more fundamental. The cell itself. Can it be alive without some parts? If so, which parts? Venter and his colleagues made a cell with scratch assembled DNA.  There have also been various attempts to make a minimum cell by removing pieces until the cell no longer functions.  I don't think this tells us very much about what it takes to be alive though.  Even a minimal cell has all the functions that we normally think of a required for life.

On the other hand, we know that to continue living, a cell must have correct DNA.  Venter's team missed a single nucleotide and the entire organism died.  It must have been a critical function for life.

I think that a lesson we could take from this example is that life has to have instructions.  It there has to be some underlying component that can tell a living thing how to do all the things that it needs to do.  Again, we often think of a living thing as reproducing, metabolizing, responding, moving, and growing and developing.  So the cell has to have the instructions to do all those things.

But leads me to a very unsatisfying definition of life.  "The ability to do all the things that living things have to do."  A better circular argument hasn't been seen, I think.  But, I think we're on a good track.  What is the purpose of life?  If you go with the selfish gene concept, then the purpose of life is to spam the environment with as many copies of yourself as you can.  What do all the copies have in common?  The genes, the genetic information to create copies of itself and the ability to keep itself alive to make those copies.

Could we define life as “the existence of genetic information (enough to operate and reproduce the organism) AND the ability to maintain and/or propagate that information”?

That one sentence, after all of ten seconds reflection, really does a nice job of summing up the functions of life and still allows room for the existence of forms of life other than organic systems (e.g. computer based life or non-organic based life).

Since the horse, as a unit, cannot maintain or propagate the genetic information it contains, it is no longer alive. Same with the apple (which is still problematic to me). For a while, the dead organisms can use internal resources to maintain, but not propagate the genetic information. But it cannot continue the process for longer than the cells have resources.

A bacterium, on the other hand, does have genetic information and can maintain and propagate that information.

The cell without a nucleus is an interesting question, even with this definition. But a little thinking about my definition might reveal a new concept (one that human scientists don’t seem to like dealing with).

Alive may not be an all-or-nothing state. It may even be reversible in some situations. Perhaps the cell, without a nucleus, is dead. But by putting a new nucleus in, then the cell can become alive again.

Thoughts?

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A vampire bat returned to its cave.  It was covered in blood.

The other bats crowded around it.  "Where'd you get the blood?"  "Look at all the blood."  "Comon, don't hold out, where's the blood from?"

Finally, tired of the incessant whining of the other bats, he said, "Fine.  Follow me."

All other bats followed him out of the cave.  The flew across the field.  They flew over the river.  Finally, they flew into the forest and landed on a tree.

The other bats were so excited.  "Are we there yet?" they cried.

"Almost.  You see that big tree right over there, the really tall one?"

"Oh yes," they all replied.

"I didn't!"

Here's another brain twister for the day.  I was kind of hoping for a particular response to yesterday's "Are Apples Alive?" post and I got it this morning (thanks Arthur).

Now, I'm not trying to be difficult I promise, but if an apple that is in the fruit bowl (we'll assume recently picked) is considered to be alive... then why is an animal considered to be dead, when many of its cells are still functioning after we declare it 'dead'?

Our organs can survive for a fairly prolonged time in the event of the whole body death.  Limbs can survive as long as 6 hours.  Bone and ligament, much longer.  Hair and fingernails continue to grow after  death.  The brain can survive for about 10 minutes under optimum conditions without major damage.  There is at least one case of a cat being completely revived after one hour of death.*

Now, I freely admit that we're moving beyond scope a bit.  We're talking about brain death and clinical death here and the prior conversations have been about living things.  But I think that this serves to emphasize a point that I made earlier.  Biology is squishy.  It is very difficult to objectively and completely define some parts of biological systems, because there are always exceptions and, thanks to 3 billion years of evolution, life is very, very tough.  To paraphrase Neil Stevenson, "We come from a long line of stupendous bad-asses... because every living thing in the history of the Earth that wasn't a stupendous bad-ass died quickly."

OK, let's get back to where we were... when considering a multi-celled organism, can we say that it is alive if all of its cells are alive as Arthur suggests?  Yes, of course, the cells in the apple are alive, but is that enough to be considered alive?  If it is, then why is our animal dead, when the majority of its cells are alive and will continue to be so for quite a while?

The direction I'm taking here, is that an apple fallen from the tree is not that different from a limb that has been severed from the body.  That part, whatever it is, can survive for a time, but it is no longer connected to the super-structure that makes the entire thing alive.  A living thing can reproduce itself in its entirety, a broken off portion probably cannot (let's not get into Planaria right now).  A living thing can intake material and energy, which is then used for maintenance, movement, response to the environment.  A broken off part cannot (again, in general, plant cuttings may work fine**).

BTW: In case you are wondering, I'm totally off my planned material at this point and thinking 'outloud'.

Can we say (should we say) that a multicellular organism is no more than it's component parts?  Or is a multicellular organism something like what we were previously talking about... is there something that makes it more than the parts.  Is there an emergent property that says we shouldn't treat single-celled and multi-celled organisms in the way (with respect to being defined as 'alive')?

But research seems to indicate that there is little difference between single-celled organisms and multi-celled organisms at some level of evolution.  This report basically describes the change from single-cell to multi-celled due to predation. (for for the Springerlink link, I thought I had the full article downloaded, but I've lost it).  So, again, life is squishy.  There's not a dividing line between single-cell and multi-celled, so it will be (probably) futile to discuss a difference between life and non-life from that angle (and thus we see an example of real science in which we take a shot and it didn't quite work how we intended).

Or do we go back to the multi-celled structure having specialized cells and all the parts can't function unless they are connected (however tenuously) to the other parts.  The whole organism can do all the functions of life, but pieces cannot.  The cells in my reproductive system, while vitally important to the whole and the species, just can't do their job without the lowly small intestine.

I very well may be obsessing about this too much and am being silly.  I don't think so, but what do I know.  I think this is very important thing to consider.  Not because we'll change the definition of life and biologists will stop studying prions or something silly like that.  I don't want biologists and computer scientists to get into turf wars over who gets to study some digital organisms and not others.

I do think, that at some point, probably in the near future, some scientists will go for it.  They will endeavor to create life in a large, complex simulation.  Maybe it will be a giant Uery-Miller set-up with clary substrates all over and pyrite chunks for catalyzing, put a wave machine in to create vesicles on the clay.  Will it work?  We won't know until someone tries.

But, if we aren't sure what life is, how will we know if they succeeded?

OK, I'll go away now, I'm just blathering.  The plan is to talk a little bit more about this concept of what is live, then get into some abiogensis research and see some of the really cool stuff that is being done to examine the questions of what is life and how did it get here?

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* Hossmann KA et al., KA; Sato, K (1970). "Recovery of Neuronal Function after Prolonged Cerebral Ischemia". Science (American Association for the Advancement of Science) 168 (3929): 375–6. doi:10.1126/science.168.3929.375. PMID 4908037.

Hossmann KA et al., KA; Schmidt-Kastner, R; Grosse Ophoff, B (1987). "Recovery of integrative central nervous function after one hour global cerebro-circulatory arrest in normothermic cat". Journal of the Neurological Sciences (Elsevier) 77 (2–3): 305–20.

** Which brings up the whole issue of stem cells.

Hi. I’m very excited to be guest blogging here. This is my first guest blogging spot, so please be gentle.

Cassandra’s Tears is where I normally hang out blogging. I attempt to make some really cool science accessible to the non-scientist. I also talk a bit about technology and the anti-science positions. Rarely, readers are treated to a bit of humor or a past attempts at short stories and poetry.

I have always enjoyed science. When I was three, I could shock anyone older than about 30 by telling them I wanted to be a paleontologist and name dozens of dinosaur genera. Over time (more than I’d care to actually think about), I learned a lot about myself.

I still love science, but I love the knowing. I’m not real big into the actual finding out. Basically, I suck at experiment and observation. I’m also easily distracted. I can’t stand to be fixed onto one subject. I’ve never gotten an advanced degree, because they don’t make advanced degrees in general science. Still, I’ve learned a lot on my own and am pretty comfortable with most areas of science.

This stood me in good stead while I was teaching. I taught, for a few years, at a tiny little school in Sabine Pass, Texas. You might remember it being run over by hurricanes Rita and Ike. I joined Sabine Pass School right after Rita and stayed until right after Ike. I taught; biology, chemistry, physics, IPC (physical science), oceanography, and TAKS prep courses… all in the same year. Suffice to say that I know a little about a lot.

I’m a huge fan of science fiction, even though there is little out there worth reading or watching nowadays.

Now, I’m still involved with both education and science. I’m a science content specialist for a company that works in publishing, education, and assessment. So, I get to read all the cool stuff and then try to incorporate that into our products. Yes, I live in a cube farm.

On Cassandra’s Tears, I’m engaged in a chapter review of The Emergence of Life by Pier Luigi Luisi. Abiogenesis is a fascinating topic and so much has been learned in just the last decade. What’s interesting about the book is that the author has included some chapter ending questions for the reader. These aren’t like ‘test’ questions, they are thinking questions.

Those are what I would like to talk about here. I think this would be a good place for discussion. I’m planning on taking a few of the questions about life and the generation thereof and giving you my thoughts about the matter. I would love to hear your thoughts on the matter as well.

“What is life?” and “Where did life come from?” are not simple subjects. I think it’s the nature of biology (being squishy rather than firmly defined).

If you think about chemistry, you can firmly declare a molecule to be of a given type. It isn’t water unless it’s 1 oxygen and 2 hydrogens in a covalently bound system. You can even talk about solutions with varying ratios of solute to water, but you can define them in very specific ways and have a standardized convention for stating how much solute, how much solvent, and the concentration of the solution. So, even if there’s a range, you still have a very specific definition.

You can't really do that for life and there are a lot of 'ifs', 'ands' and/or 'buts' involved.

So, that's what we'll discuss here. Totally new, totally fresh, so let's get the ball rolling. What do you think a good definition of life is?