Is Intelligence a Biological Imperative?: Part IV
The Drake equation was developed as a means of predicting the likelihood of detecting other intelligent civilizations in our galaxy. At the forum, Frank Drake, who formulated the equation 42 years ago, moderated a debate between Peter Ward and David Grinspoon.
In this installment, the three participants respond to audience questions about the biological aspects of the Drake equation.
Previous parts of this series presented the opening remarks by Drake, Ward and Grinspoon. The final part will present the remainder of the question-and-answer period. Parts1 * 2 * 3 * 5
|Artist conception of the K/T impact event.
Q: I'm having a little trouble with the concept of long-term stability being necessary for evolution, because it's my understanding that we've discovered in the last 30 years or so that what drives evolution is instability, rather than stability. The dinosaurs had a long reign on Earth, and it wasn't until an impact that things really changed and more development happened that led to us. So could you elaborate more on the factors that you see as necessary stability vs. necessary instability for evolution of intelligence?
Ward: I think it's the degree of instability we're talking about. Look at climate. Seattle has just gone through 90 days without rain. This is a record. This has never happened in Seattle's history. Ninety days, not a drop. It's been great. I'm brown. This is, like, amazing. We can live with that sort of instability. But there are trees up there that are dying like crazy. And as I flew down here tonight, the entire Cascades is on fire. Well, this is like minor instability.
But the instability that I worry about is all of a sudden, tomorrow, it's 200 degrees on the planet, and you're all burning up in your beds. Now that's the sort of instability that's too unstable. So, you're right. Small-term stuff creates evolution. Right now, plants are figuring out, well maybe since I live in Seattle now it doesn't rain very much, I can't last through this. I've got to be a plant that can last through three months of no rain. So evolution, natural selection is at work. But when we get to instability that's so great that it kills everything, it's over the top. So we're talking about minor versus major.
Grinspoon: But, of course, it's relative. You can imagine creatures evolved on a planet something like Venus, that doesn't really have seasons, having this kind of a discussion and talking about why Earth is uninhabitable because of these horrible seasons, the fact that it goes from being frozen to being hot, over and over again.
So it seems like a characteristic of life is that there are limits to the variability of environment that it can tolerate, yet there's a certain amount of variation that life seems to thrive on, or at least adapt to, and we certainly do not know what those limits are. So when we talk about planets that are tidally locked, and have one side that's very hot and one side that's very cold and say that that's uninhabitable, I think we have to think of the lesson of the Venusians who think that Earth is uninhabitable because of its seasons.
Image Credit: Trustees of Dartmouth College
Drake: I want to add just one comment to this. The degree of instability is, of course, important. If you get to a temperature that is lethal, that's the end of things, and similarly if you freeze the planet. However, with lesser instabilities, you have to take timescale into account. That is, if it goes from a temperature in California, typically, of 70 degrees, as we have now, to zero Farenheit overnight, there's big trouble. But if that happens over a period of hundreds of years, people adapt. And that's the point: that life can adapt or move or migrate, or whatever, if the timescale allows. So, in considering what the impact of instability must be, it's not only the magnitude of it but the timescale.
Q: There's something that confuses me between rules in the world of the biology and rules in the world of physics, specifically thermodynamics. We evolved to be complex and intelligent because the mutations that brought us here didn't prevent us from doing that. But the rules of thermodynamics favor randomness and disorder. So, how does life, which favors complexity and orderedness, exist in a Universe where thermodynamics really is the larger ruling pattern?
Grinspoon: Well, you've hit on a wonderful question that was examined in a couple of classic books, most recently by Freeman Dyson, but before that Schrödinger. There have been three or four asking exactly that: In a thermodynamic Universe, how could you expect to have life? What is it about life that allows its continued existence?
One way of looking at it is there's something called non-equilibrium thermodynamics, where you develop spontaneous pockets of order in the presence of a flow of matter or energy. A very simple example is a whirlpool, where you have a flow of water and in certain conditions you develop this order. Well, the same thing happens with certain kinds of chemical reactions: If you have a flow of energy, you create order. And so it's a seeming violation of the second law of thermodynamics, but it's not, really, because the system is out of equilibrium.
There's this whole new field of complexity theory, which is the study, essentially, of self-organization, or non-equilibrium thermodynamics. One way of looking at life is that it's the most extreme example we know of self-organization. The Universe clearly has a tendency to self-organize in certain non-equilibrium conditions. So there isn't really a violation of the laws of thermodynamics there. It takes a flow of energy. And even though we have disagreements about what conditions might be necessary for life in the Universe, I think one thing we can all agree on is that it will require a source of energy and a flow of energy and matter because it requires disequilibrium to exist.
|All life on Earth is DNA-based.
Image Credit: Wikipedia
Q: I'm puzzled by a paradox. Biological life is evidently incredibly complex. All life appears to be DNA-based, it appears to have only evolved once. Take that on the one hand. And then, on the other hand, look at what people are doing on computers, where if you set up a fairly simple framework, like the Game of Life, set up some very simple rules, you can very quickly develop these very complex reproducing things, albeit in virtual space. But it seems like there should be chemical analogues to that. So my question is: One, why, if Earth is so friendly to life, is there only DNA-based life and none other; and two, why isn't there more work being done to try to find real-world analogs to what is being done in computer simulations, to find alternative types of life?
Ward: Both are being done, actually. Some of the best minds on this planet are trying to figure out, starting with Miller-Urey, really, can we ever create life in a test tube? And what you're asking is: Why haven't we done it? Well, I'll go back to the computer simulation. What a computer is is simply a binary code. Sooner or later, you're looking at plus-minus. And then you're just expanding that outwards. Your computer simulations are so infinitely less-complex than the simplest species of bacteria. When you look at what it takes to be a bacterium, compared to just the simple codes of your little Game of Life, we're talking great differences.
Grinspoon: And part of your question was: Why aren't there other kinds of life on this planet? And I think one answer to that might be that once there is one kind of life, it changes the conditions under which the origin of life can happen. In other words, once you already have DNA-driven organic life, then no other possible kind of life, even if it could work well, stands a chance of evolving, because the extant life has the advantage, and will gobble up any juicy morsels of free energy or any tempting organic molecules. It's no longer a level playing field once life gets started.
Q: There are 10 million species. Why wouldn't there be more than one life chemistry?
Grinspoon: Think of Microsoft.
Q: I don't want to.
Grinspoon: But that's my point. Once there's an operating system, it's no longer a level playing field.
Drake: To put it simply, once there's a very effective way of life, any other kind of life that forms becomes lunch.
Image Credit: NASA/CXC/Rutgers/J. Hughes
Q: You could think of the Drake equation as being be sort of three-dimensional, relating to a volume of space. But what about about how it changes over time? It seems you'd have a likelihood-of-life curve and boundaries over time. Are we at the end of it, or the beginning?
Grinspoon: I think you're absolutely correct that, if we really want to try to calculate the number of intelligent civilizations, time ought to be in the equation. All of these factors are varying with time. The number of planets is not remaining the same, the types of stars are changing, the number of planets with life is probably increasing over time, and also if intelligent civilizations can achieve effective immortality, where they exist for billions of years, then you can imagine these immortal civilizations are accumulating over time and the number of civilizations is probably rising. That's what I personally believe.
Ward: Let me give a real quick take on that. Let's say from the Big Bang, how soon after the Big Bang could we have any life? And people are suggesting that in the first 2 billion years, you're not going to get any life at all. Because you have to have stars that go through their life cycle and get to supernovae so you can get heavier stuff. You can't get heavy stuff unless you have supernovae. First two billion: nothing.
Now friends of mine, Guillermo Gonzales among them, are suggesting that the types of supernovae we need to produce radioactive heavy stuff - I'm a plate tectonic lover, being a geologist, and I tend to think you need it, and if you need it, you need a core that has radioactive material within it - those types of supernovae are diminishing. And so we may be in a case where, if we go a few more billion years down the road, we can't build habitable planets.
Q: I'd like the panel members' opinions on what kinds of science you see going on right now that are most likely to reduce the uncertainties in the terms in the Drake equation. If you look ahead just one to two decades, which terms in the equation do you expect us to make the biggest dent in the uncertainty of?
Grinspoon: There's one of these numbers that we don't know now that we will know in two decades, and that's Fp, the fraction of stars with planets. There's a spacecraft called Kepler that might help us pin down this number. And not just the fraction with planets, Fp, but the fraction with planets in the habitable zone, Ne. I think those two numbers stand a very good chance of being really nailed down within the lifetime of most of the people in this room. And the other ones, I think we're still working on.
|An illustration of the Kepler spacecraft.
Image Credit: NASA/Ames
Ward: Some of the experiments that are most interesting to me at the moment are not those that are actually observing real things, but are taking place in computers. And some of the most impressive work that I've seen is the modeling of solar-system formations and especially the work that is asking: When solar systems form, how often do you get oceans?
The Earth is inside the snow line. We shouldn't have all of the water that we have, according to some of the models. And if we replay this over and over again, how many times do we get an Earth-like planet that has an ocean, or an Earth-like planet that has too much ocean? And that's some of the interesting stuff, too.
We're going to find out how much is too much, if there is such a thing as too much ocean. And how much land do you need. We're going to find out, on the size, if we're say at half an Earth size, an Earth size, 1.25 Earth size, 1.5 Earth size, can planets like that support plate tectonics? And there's a member of our NAI (NASA Astrobiology Institute) team at the University of Washington, Slava Solomatov, who's closing in on that now. He's looking, using his models of different planetary size.
We're looking at how important Jupiter is. Without Jupiter, George Wetherill suggested in 1995, the impact rate on Earth would be 10 thousand times greater than it is now. Now if we didn't have Jupiter, and we only had Saturn, would Saturn do it? If we had a Saturn in Jupiter's orbit, would we have an impact rate as we do? And we're working on these things. This relates to the question of mass extinctions. When you get clobbered, if we have a hit, a Chicxulub-type hit, or any sort of asteroid hit, every year, year-in, year-out, what happens to your ability to have life on a planet? We'll find these things out.
Drake: As I mentioned, one of the most controversial factors is Fi, the possibility of intelligence evolving, the fraction of biotas that have an intelligent species. And there is a research opportunity that has just never been carried out, because the resources haven't been available. And that is to do a much more thorough study of the fossil record to determine the real mathematically quantified path of brain evolution.
Is the evolution of the brain and the size of the brain a random walk? Or is there a driver? If it's a random walk, intelligence may never occur. If there's a driver, intelligence is probably inevitable. And, it may seem a little strange, but in fact, there is probably enough data available from the fossil record to determine whether the evolution of brain size is driven or a random walk - and it hasn't been done.
This story has been translated into Portuguese.
Related Web Pages
Rare Earth Debates: Complex Life
The Search for Life in the Universe
The Search for Distant Earths
Extrasolar Planets with Earth-like Orbits