Tuesday, November 13, 2007

On the Fourth Day, Part 2: Survival Through Embrace

This Halloween, we went with a Veggie Tales theme: Sam was Bob the Tomato and Aidan was Larry the Cucumber. Next year we’re thinking Mario and Luigi from Super Mario Bros. may be in the cards. It’s good you don’t mind (for now) dressing up in complementary outfits, not only because it makes planning that much easier, but it points out the unique bond you have as brothers. Each of you isn’t complete without the other.

Brothers and sisters find they need each other (and become really annoyed with each other as a direct consequence). Walt Disney may have been more famous, but he needed his more down-to-earth brother, Roy, to tell him "no" and to keep his finances in line. Neither was whole without the other. These relationships, of brother to brother and father to son, form the core of books like Proverbs.

Just the other day, someone asked you, Sam, for your favorite color. You said, “Red, because my brother’s hair is red.” Aidan on Thursdays always looks forward to getting Sam from preschool: I hear over and over, “We go pick up Sammy now?” There’s no little brother or sister for you two yet: if and when one comes, our whole family will shift, and the addition of one more member will change the rest of us forever.

It was the same way with life, once brothers and sisters started to happen and become more and more different. All life looked alike for a long, long time, but once in a while, the cascade of chemicals being eaten and pooped out included a bunch of carbon atoms and double bonds fused together into something that was colored in the visible-light range. This would be the first pigment. This colored molecule could absorb the light from the sun (try putting on a black sweater and sitting out in the sunshine sometime to see what a little color can do). This molecule could get hot from the newly revealed sunlight, or maybe the energy could be funneled into one of the electrons and then carried elsewhere. If something happened to be around when the sun was out, this energy could run into it, then a whole new class of reactions would suddenly become possible. The fortunate little bug would be suddenly solar-powered, and it would be able to catalyze reactions no one else could do. For instance, that solar energy (photons) could be put to use piecing together carbons into more complex structures (synthesis): and then you’d have your first little chemist doing “photosynthesis.”

Once the relationship of the fourth day was established with the unveiling of the sun, the photosynthetic organisms would have an explosion of energy that they could use to do all sorts of things. We already talked how there was so much photosynthetic activity that the very composition of the atmosphere changed, and it became charged with oxygen. Then other reactions could use the oxygen. Strike a match, and you start a reaction between the oxygen in the air and the carbons in the wood (and step out of the way, because that’s an energetic reaction you just started). Some of the other bacteria on the fourth day started catalyzing similar reactions, burning carbon and oxygen, producing carbon dioxide, and then specializing by running other interesting reactions with the leftover energy. Let’s call these bacteria the “pyrotechnic” bacteria. Then the carbon dioxide would be swallowed up by the photosynthetic organisms, producing more oxygen, which was captured by pyrotechnics, etc. etc. etc.

Note how, in the relationship between the photosynthetic and the pyrotechnic bacteria, each requires the other. The waste for one is the food for the other. This is a stable relationship of more than one part, a relationship like the sun and the earth. I’d say the sun and earth would be a dependent relationship; photosynthetics and pyrotechnics would be an interdependent relationship. But for all the relationship, there’s still two separate little bugs swimming around, each with different jobs, but not too different and not too complex, really. Not yet.What came next on the fourth day was another remarkable leap. Remember how each bacterium has an oily fence of a membrane around it? Like soap bubbles, two bacteria can sometimes merge into one. And once in a long while, if you’re lucky, you can blow a special bubble with a small bubble inside of a big one, right? Well, bacteria were able to do that too. Instead of fusing into one bubble, each bacterium kept its own bubble, so that one was inside the other. At that point, two organisms became one, but each kept its identity, and a new chapter in life’s complexity started. This is even more intimate than a marriage: it’s like a birth in reverse, with a mother cell engulfing a “baby” cell.

There’s a complex interplay of trade-offs going on at this stage. The inside cell loses its freedom but gains protection from the elements outside. The outer cell must feed the inner cell, but it gains whatever new reactions the inner cell can catalyze. If the inner cell is very different, then the outer cell gains a whole new set of reactions, and maybe it can live in a different environment all of a sudden. On the whole it must have been worth it, and these “married bacteria” must have survived better, and producing more and more bacteria like them. This new relationship that led to life was a vivid embrace. It wasn’t just a survival of the fittest, but also a revival through embrace, a model of cooperation instead of competition. The new cooperation cost a lot of energy and a lot of freedom. In the end analysis, it was a very good move, because we see it working everywhere now. Look inside a photosynthetic plant cell and you will see tiny green baby bacteria called chloroplasts:

These trap light and carry out the reactions that produce oxygen from plants. I think if we’re to reduce carbon dioxide levels in the atmosphere, we could repeat the same atmosphere-transforming trick from millions of year ago by harnessing tiny green chemists to convert carbon gas into carbon solids.

It’s not just plants that have subcellular sidekicks, but you do too. Look inside your cells and you’ll see red-brown blobs with a distinctive wrinkled shape:

(Image from http://mosslink.biz/webimg/bumble_bee_mitochondria.GIF)

These are your mitochondria, and they carry out reactions opposite to the chloroplasts: like tiny internal combustion engines, they burn oxygen and spit out carbon dioxide. On that level, it’s almost exactly like the reactions in your car engine, but much more controlled and efficient. In tissues that need to use a lot of energy, like muscles, the cells can have thousands of mitochondria, more than Jay Leno has cars.

So inside most of the cells of your body, there are hundreds of mitochondria along for the ride. They make up a significant proportion of your weight. But don’t get upset, they pay their fair share: after all, where would you be if you couldn’t breathe in oxygen for energy? You’d have to be green and rooted in one place, that’s what. Higher brain function is very energetically expensive, and practically requires a complex, specialized engine like a mitochondrion to work at all. If you can read this, thank a mitochondrion. (And this is why biochemists shouldn’t write bumper stickers.)

The proof of this theory (called the endosymbiotic theory) is all around on the biochemical level. You can pretty easily pull mitochondia and/or chloroplasts out from a bunch of cells with a centrifuge. Then you can compare the “little baby bubbles” to the larger cells, and to bacteria. You find that some of the molecules match and some don’t. In fact, in every category we biochemists can come up with: proteins, DNA, RNA, membranes, sugars, you name it, chloroplasts and mitochondria look like bacteria, and they don’t look like the larger cells that surrounded them. You can take a piece of a chloroplast that makes proteins, and put it into a bacterium, and it works just the same -- these parts are interchangable!
Chloroplasts and mitochondria even reproduce like bacteria do. For chloroplasts, we can even find a bacterium that looks so much like a chloroplast that it’s got to be the source bacterium, or at least a cousin once removed from the source. Also, we can find small bacteria that have taken up residence in larger cells, but have not yet lost their identity to the other cell. Aphid gut cells contain lots of spherical bacteria that live inside and appear to be in the process of becoming permanent parts of the aphid. Therefore, we’ve found intermediates in the process, and evidence of end points all around. Not only has it happened repeatedly before: it is happening repeatedly now.

Mitochondria and chloroplasts are just the sub/intracellular examples. Don’t get me started on the extra/intercellular examples: the bacteria in your intestine that you need to digest your food, or the bacteria in plant roots that can uniquely grab nitrogen and break it apart into ammonia. These examples are so important that I think it’s fair to say that cooperation and relationship are at the heart of life, and are at least as important as competition and individual survival. Darwin is part of the story, but so is sacrifice for the good of the other.
Embrace, then, is part of creation. Miroslav Volf’s book Exclusion and Embrace uses this same word to sum up a discussion of forgiveness and justice for the church. To join the body of Christ is to lose your identity, even dare I say, to be “born again” into something rather than out of it. They’ll know we are Christians by our embrace. And embrace is costly, whether it kills us outright or causes us to lose our rights, or even what we cherish as our identity. Scary stuff, and easy to misinterpret, even easier to leave uninterpreted. I’ll let Volf’s amazing book speak for itself when it comes to the theological meaning of embrace – I will put this forward as one biochemist’s version of a scientific meaning.

The importance of cooperation intensifies when you realize that there’s a third, in-between state of cooperation between organisms. I’ve mentioned how separate organisms can cooperate from a distance, or can embrace to become one. Between these two extremes you can find the case where a bunch of single cells start to stick together into a blob, or to use the technical scientific term … a slug (hey, it’s not always complicated).

Consider the slime mold! When times are good, slime molds will exist as individual amoebae, tooling around independently, gobbling up the food, and watching the Spike network. But when the food runs out, they suddenly start to stick together, aggregating into a slug. They change in the process. Some cells become front cells, some become back cells, and the whole thing starts to act like a single animal: it can sense light or food, and it moves together as one. Now, this is probably beyond your time, but I just have to mention that reminds me of nothing so much as Voltron, Defender of the Universe. In other situations, this slug can change into a stalk that acts like a spore. At this point the scientists ran out of words that start with “s” and just published the data.

(Image from http://cosmos.bot.kyoto-u.ac.jp/csm/photos/V12M2_plate.jpeg)

(Image from http://cosmos.bot.kyoto-u.ac.jp/csm/movies.html. The top is a slime mold aggregating into a slug, and the bottom is a slime mold slug lunching on surrounding bacteria.)

This transforming clump of cells was like another innovation that had to happen during the fourth day. When a bunch of cells get stuck together, different jobs get handed out to each one. Because of this, cells could specialize and cooperate, and another dimension of complexity could develop. Some cells could become eye cells, and some finger cells. It’s worth noting that each cell is important to the whole, and each function is needed, whether spectacular or mundane, public or private. It seems to me someone has hit on this (First) idea (Corinthians) before (chapter) but (twelve) I’m blanking on it right now ...
Some slime mold cells have specialized so much that they are equipped to seek out and destroy threats (including but not limited to other slime molds, no doubt). These sentinel cells perform the same function as our immune system, and show an amazing degree of specialization for something as lowly as a slime mold. And how do these sentinel cells take care of offending bacteria? Just like the whole process started, by engulfing and "embracing" the bacterium, just before atomizing it (hey, no one said every embrace was going to be sweet and tender!).
It’s worth noting that your own body is an exquisite example of specialization, with the immune system in particular being a proficient (if costly) example of how certain cells can take jobs no other cell can, and the end result is a system that can move, change and adapt in its mission to sniff out and attack germs.
In conclusion, life is found here, in relationship and cooperation. We are not just autonomous units fighting all the time, but we are carrying around pounds of bacteria, both inside and outside of our cells, that work with us to eat food and produce energy, so we can think about … those bacteria. In the context of life, death and suffering, an ineffable goodness is to be found in parts relating to become more than their sum. To put this principle into equation form, 2+2=5. I can imagine that God saw this and he said that it was good.
And so I’ll suppose that He did. On the fourth day, the biochemical blueprints for diversity were laid in the complex relationships of single cells, and they became more than single cells. Some became smaller and lost identity, some stuck together and gained a renewed identity as a microscopic body. Following this same template of creation, the next day would be an exponential explosion of diversity, life, and death, finally visible to the watching eye, as creation accelerated toward its end.
It was evening, and it was morning. The fourth day was done.

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