Saturday, November 19, 2011
The question of what is alive and what is not alive at first seems fairly easy to answer. Animals, plants, bacteria, etc. are living things and rocks and minerals and air are not living things. However, in science, it's never quite so straightforward (well, sometimes I guess it is but not here). Most biologists would agree that life has seven characteristics. This description may be dull but it's important for the point I want to make...I'll try to be succinct:
1. Homeostasis: your insides stay pretty constant all the time. You've got a constant temperature, for example.
2. Organization: you've got cells. You're not just made of free flowing energy or some kind of gelatinous mush.
3. Metabolism: Your cells can convert energy (food). You need to do this to maintain homeostasis and to grow and so forth.
4. Growth: yup, you started off as a single cell and now look at you!
5. Response to stimuli: Things that are alive react to the environment. Fire bad!
6. Adaptation: No one organism can do this but populations of organisms, over evolutionary time, change by means of natural selection to become better suited to their environment.
7. Reproduction: things that are alive can make more of themselves.
So that seems pretty exhaustive and it does a great job of explaining the unique characteristics of, say, an animal. Animals all eat and grow and evolve and all that good stuff. But there are some things in the natural world that look like they really should be alive but aren't and some things that seem like they really shouldn't be alive but act like they are.
Viruses are science's most notorious culprits for looking a lot like living things but not fulfilling all seven criteria. Viruses reproduce (that's what's going on when you have a cold, they're invading your cells and making more of themselves) but they can't do it by themselves; they've got to have a "host." Viruses definitely adapt, that's why everyone's worried about the potential of "super viruses," because they do evolve and (for example) become resistant to antiviral agents. They have organization even though they don't have cells but they don't grow and they don't really respond to stimuli, or at least not in the sense that we normally think of stimulus and response (even single celled amoebas and things like that look more like they have "behavior" in the way we tend to think of that phenomenon).
So scientists have been stymied over whether or not viruses are a life form or not. Perhaps they are some thing that's not life but not not alive either...maybe we just need some new language.
I've been thinking about this recently for two reasons: a friend of mine told me that scientists have observed metabolic reactions (chains of molecules processing "food" into other stuff) happening outside of "living" cells. I don't think anyone wants to claim that these metabolic reactions are alive just as is but it raises some interesting questions about how life began and how life works and what exactly the differences are between "living" and "not living."
And finally I watched this TED talk the other day. You should just go ahead and watch it. I'll wait....
I know, crazy, right?! That bit where the "cell" splits in two, essentially showing reproduction happening in a system that for all intents and purposes is "not alive" is just so cool and bizarre and throws a lot of other assumptions about cells and life into question.
Or maybe it doesn't. Maybe it just teaches us about what things on primordial Earth were like. Maybe viruses sort of do the same. Maybe 3.5 billion years ago there were lots of things that were sort of alive but by means of natural selection and competition the truly alive mostly won out. One thing is for sure: that's some pretty neat science.
Friday, November 11, 2011
When we first learn most categories in science we draw black and white distinctions. It helps, I think, to make broad and gross categorizations when first learning. Mammals are warm blooded. Reptiles and fish are cold blooded. These are traits that the groups mammals, reptiles and fish have.
This, of course, is really not the case. Like most broad and gross characterizations in biology these rules are broken. There are what we call "warm-bodied" sharks and bony fish, such as the blue-fin tuna. They produce internal heat in a different way from birds and mammals but they are certainly not truly cold-blooded.
While researching warm-bodied fishes for a class I'm teaching I came upon a surprising natural history factoid: swordfish are warm-blooded...but only in their eyes. Unlike the "warm-bodied" sharks and fishes the swordfish heat production is much more like a mammal's. We have cell-parts called mitochondria (you may remember them as the "powerhouse" of the cell from high school biology) in higher density, especially in certain types of tissue. These mitochondria are responsible for metabolizing ("burning") food into energy on a cellular level. When these mitochondria metabolize food one of the byproducts is heat. So by having a high density of these cell parts you get more heat.
The muscle tissue responsible for moving the swordfish's eyes are also, like certain mammalian tissue, packed with mitochondria. These specialized muscles help to heat the animal's eyes and brain. Warmer eyes mean sharper vision, great for a large predatory animal, and a warmer brain means faster processing speed, which seems great for just about any organism.
It makes me wonder why mammals and birds evolved endothermy (a general term for any organism that produces heat from within its body regardless of how that heat is produced) but fishes which have been around a heck of a lot longer only a have a few representatives with this adaptation. Will there be more warm-blooded fish in another fifty million years?
Wednesday, November 9, 2011
So apparently this video has gone "viral." If you haven't seen it...it is pretty neat:
I looked into how starlings do this. The answer being, we don't really know. This article from Wired was just published yesterday:
I checked my usual science blogs and none of them had posted anything about it. Carl Zimmer, where are you when we need you, man? So the article essentially speaks for itself. The birds overall behavior looks more like boiling water than animal behavior. But what does that mean?
What I think it means is that the birds have some way of sensing what's going on with many if not all the other birds around it that we don't understand. Behaviors don't just happen so unless starlings are actually some kind of future alien robots with quantum computing capabilities in their brain that allow them to sense things free from the bonds of time and space they must be "communicating" in some way.
It reminded me, initially, of schooling fish. Fish all have a sensory organ called the lateral line (the next time you see a fish take a look at it's side: many have a visible line down the middle. Cod, for example, have a very noticeable lateral line). The "organ" is actually a series of mini-organs, pits with sensitive hair-like structures that sense pressure differentials (i.e. moving water). Because the fish can sense differences in pressure so acutely they "know" what the movement of their neighbors and their neighbors neighbors is like and can adjust their movement accordingly.
Now birds don't have lateral lines...they are derived bony fish, though, so maybe...
It reminded me of another natural history story, though. Dolphins can do something really odd. When a trainer has worked with them the human can ask a pair of dolphins to do a novel behavior together. Without making any detectable sounds the dolphins will swim to separate parts of a pool and do a behavior neither of them has ever done before at the same time. And we have no idea how this happens. We assume the dolphins must be communicating. We just have no idea how. All of our attempts at measuring the communication have failed.
We tend to assume things with animals will be nice and easy, that they won't do things that defy our recording equipment or appear more like particle physics but then something like this comes along like this. I'm betting this won't be resolved for a long while, usually some scientist has to really overcome the standard thought about how things might be working to solve a problem like this. And it'll probably be really cool science when that person comes along.