Transcript from Epic of Evolution: Life, the Earth and the Cosmos (BEP 210A)

April 26, 2000 - Lecture by Michael Wysession

WARNING – This Lecture Has Not Yet Been Edited.

It Will Eventually be Replaced by an Updated Version.

Okay, let me get started on this class. There are a couple things I want to do today. Well, at the very end of the class I’ll leave 15 minutes to do the course evaluations so if I start putting you off to sleep during the middle of the lecture you can go ahead and fill in some spaces during the class, but otherwise I’ll give you plenty of time at the end of class to do that. And before that, the last thing I’m going to talk about is what is on the syllabus for this class and that is are there any more Earths? And I’ll refer to something called the Drake equation, which is a computation for how many other intelligent civilizations there are in our galaxy.

But before I do that I want to cover one aspect of geology and earth science and that I haven’t really touched upon. It’s a special class of rocks and they’re called fossils and I’ve got a couple samples here. Here’s the lower jaw of a baby mammoth that died right when it was born. This was found a couple hours drive south of here. There’s actually a Mammoth State Park where a lot of fossils are found. And we learn a lot from the history of life by looking at the various fossils and the way the fossils are shaped. For instance, you’ll notice the teeth here have very flat tops on them and that’s because these were herbivores that ate essentially prairie glass. Mammoths lived tens of thousands of years ago (not very long, this is a very young fossil) and its teeth were specially adapted to what it ate. We can contrast that with a little bit of a mastodon jaw and here’s one tooth from that mastodon and you can see it’s shaped very differently from the mammoth tooth and it ate a different sort of vegetation. It ate a much more varied diet of plants and branches and trees and its teeth reflect that difference in diet. I have just a couple other things here. Here’s an example of a fish and I can actually stand this up and this is from the Jurassic so this was somewhere between 150 and 200 million years ago. And here’s a skull of the ancestor of sheep. This is an oreodont. This lived about 40 million years ago or so. And the last thing I have we think is the femur from an herbivorous dinosaur but we don’t know. It was found in the back of the drawers of our collection and it wasn’t labeled and our paleontologist thinks it looks like a dinosaur femur (essentially a leg bone) but we haven’t been able to identify it. These things are old, hanging around a long time.

The amazing thing though is by looking at this whole history of these special rocks dug up out of the ground we’ve been able to get a rich understanding of the history of life on our planet. I mean I happen to think rocks are really cool but really the most fascinating, complex thing on this planet is life in the many forms that it’s taken. Ursula has talked a lot about how life works and how it’s formed. And you see here in this picture that really for almost all of history life was one-celled, you know beginning as Prokaryotes. And I have bacteria next to that but let me just flash for a moment to this picture similar to what Ursula showed, and another way to put the tree of life has sort of bacteria type organisms on this end. This is going by their genetic structure. The Archaea, another type of one-celled organism here, and then Eukarya, more complex one-celled organisms, and then like way off at the end here you get everything else -- all the metazoans, multiple-celled life of which Homo, we are, you are here, right out here. And it’s kind of humbling when we look at the diversity of life that exists simply at the single-celled level and realize that in terms of number of species all the multiple-celled life is kind of an afterthought. But nonetheless we’re the afterthought and we have to view things from our perspective. We can’t avoid that. And so here’s sort of a chain of evolution from our perspective and from more complex one-celled eukaryotes and we have fossil remains that go back about 1½ billion years of eukaryotic life. There are the fungi, animals, plants.

And the whole history of plants is fascinating. Of course it began in the oceans but then vascular plants developed that were able (like moss) to live on land. And starting a little more than 400 million years ago plant life began on land and that essentially opened up a whole new ecological arena for animals. The original life was very simple -- ferns and gymnosperms. Ginkgos for instance are some of the oldest things on Earth. We have a ginkgo tree right next to Holmes Lounge just north of us and this is an incredibly primitive life-form. It’s been around for hundreds of millions of years and eventually it figured on the technique of pollination and having flowering plants and angiosperms kind of took off from there. But that required some complex symbiotic relationships with things like bees and others that help in that pollination.

The animals, for a long time we had a variety of experimental forms. I mentioned one particular Burgess shale creature (a chordate) called a Pikaia and from these chordates we have a history that leads up to us, essentially of worms. And by the way I didn’t say it earlier but we owe our existence to worms. In more ways than one it was worms churning up the sediment at the bottom of oceans that kept carbon and carbon dioxide recycled in our atmosphere and probably prevented the Earth from flipping back and forth into these giant snowball conditions that had prevailed before this time. And the worms are really responsible for setting the Earth on a level of stable climate.

And then we have the history of vertebrates. The initial fishes were armor plated and they had no jaws even and then you developed the skeletal bony fishes. The early fishes in fact were cartilaginous, many of them like sharks. And shark is another very primitive life-form, very efficient, has managed to survive amidst all sorts of other environmental changes. Lobe-finned fishes were important because they led to amphibians. We have some samples of lobe-finned fishes. There was an example called the Latimeria (or Coelacanth). It was actually found originally off the coast of Madagascar and now off the coast of India as well that is essentially unchanged from over all this time. And amphibians had the ability to go up on land and back, and from amphibians led to reptiles which were able to live -- amphibians lay their eggs still in water; reptiles have their eggs encased in shell and so it could live entirely on land. And of course a variety of things happened from there. Some reptiles went back into the water and we had things like mosasaurs and plesiosaurs, essentially ocean-going dinosaurs that lived.

And I’ve drawn these perhaps the wrong way. I probably should have put birds next to dinosaurs. It turns out that dinosaurs come in two flavors. One’s more similar in skeletal structure to lizards and one is more similar to that of birds (the saurischians and the ornithischians). And there’s an interesting debate about dinosaurs and many of you may know that a lot of people now think they were actually warm blooded like mammals. The first mammals evolved actually a long time ago (probably about 250 million years ago) and they were essentially rats. One of the oldest is something called the Morganucodon. It’s a rodent-looking creature, and we evolved out of that form. And mammals take a variety of interesting forms. Some of them lay eggs like the platypus (the monotremes). Some of them have their young develop in a pouch like koalas and kangaroos (marsupials). Most fall under the category of placentals (they give live birth) and of course there’s a wide variety of mammals. And about 50 million years ago or so we began to have the early primates and again that’s our line of evolution and sometime back our lineage split off from that of the rest of the apes (the prosimians) and led to the hominids and humans. About 5 million years ago or so our early sort of human-like ancestors like Australopithecus, we’ve found fossils of those largely in places like Ethiopia and Kenya in Africa.

But the whole history of this is absolutely fascinating because what we find when you look at the skeletal structure is we see evidence over a long time of a variety of behaviors that we see working now and the message is that evolution and the mechanisms of evolution (reproduction, selection, mutation) are incredibly powerful and incredibly efficient at searching out any possible way to live. And so we have life-forms existing in every imaginable ecological niche and even many unimaginable ones -- inside of rock, within ice at the South Pole, tops of mountains, bottom of oceans. It’s really incredible the range -- huge range in temperature, in pressure. And just to give you some examples of how life has evolved through this fossil record, we see evidence of survival of huge environmental changes. For instance, there are certain amphibians that can be totally frozen in ice. Their blood contains natural antifreeze and then when the ice thaws they thaw as well and they go on living. There are certain pine cones for example that only open up and release their seeds when they’re caught in a severe forest fire. So in other words, you’ve got a forest, it totally burns to the ground, then the seeds open and you have your first line of succession of your new forest. So this is a mechanism that has evolved. It has no competitors when everything’s burned to the ground and it’s the first line of trees that come back up.

We have incredible mechanisms of dispersal. For plants we have spores and seeds and every time you walk in the field your socks are covered with little burrs sticking to it. These are incredible ways these seeds have found to get around. For animals there are all sorts of bizarre ways of locomotion -- flying, swimming and crawling. And it’s fascinating to see how populations of species can disperse across wide areas. We even see that during modern times. The annoying flocks of black birds called starlings are a good example. They were introduced here from England sometime I think in the last century and have essentially just spread across the country and taken over many ecological niches that other birds had originally had.

Predation has been a remarkable aspect and early on as soon as you had multicellular life you had some animals eating others. Teeth, stingers, poison, we even have plants like the Venus flytrap that eat animals. Of course you had then evasion, camouflage, speed, having multiple offspring -- ways to avoid getting eaten. For instance, some species of sea turtles are born in the sand and all the females come up, lay the eggs at the same time, all the eggs come out and you just get millions of little sea turtles trying to make their way across the sand, through the shallows and into the ocean. Most of them get eaten by birds and other predators but there’s so many of them that some of them and a large majority still make it and that’s its evolutionary technique that essentially overwhelms its predators. They can’t possibly eat all of the turtles all at once.

We see that in other things. Cicadas for example will often lie dormant for an odd number of years (like 13 or 17). So that’s very hard for a predator to predict when suddenly the whole area is going to be swarming with cicadas. The birds are going to have a field day at that time but they can’t possibly eat them all. They lay their eggs in the ground and they lie dormant again for some odd number of years and then they come out again.

And we see within this incredible dynamics that occur in populations between let’s say predators and prey. One of my favorite examples is the prickly pear which is a cactus that’s native to Central and South America, and it’s a nice garden plant and there are many varieties of prickly pear. They had been introduced in Australia in 1839 for gardens and they escaped out of the garden in a sense and by 1925 there were over 60 million acres of Queensland, Australia that were densely covered with prickly pear. You just couldn’t walk through them and it was rapidly expanding. It liked the climate of Australia and it was just thriving beautifully. Well, they tried cutting it down, burning, everything. Finally they realized well, let’s find one of its natural predators so they began to bring in several insects from Central America that laid its eggs in the cactus that ate the prickly pear and they eventually found a particular moth called Cactoblastis cactorum and within a few years the whole population of prickly pears was just decimated and cut back down. Of course then the moth population died down too because it didn’t have any more prickly pear to eat and since then there have been little flare-ups of the cactus and then flare-ups of the moth population and then they both crash down again and they go through this funny dance continuously over time now.

Other fascinating ways that animals have evolved have been symbiosis. Even the mitochondria that are in our cells are sort of in a symbiotic relationship with us. Our body is filled with these mitochondria but they’re kind of their own organisms -- they reproduce independently, they carry their own genetic material. And there’s a case of a vitally important symbiotic relationship. Your stomachs are filled with bacteria that you need to digest your food. You know this if you’ve ever taken antibiotics that kill all the bacteria in your stomach. You have often have to spend a lot of time in the bathroom because you can’t digest your food very well, you need that bacteria. Certain animals like termites only are able to digest their food with colonies of bacteria that digest the wood and so they would not live if they didn’t have these large colonies of bacteria in their stomachs.

There are fascinating examples between plants and animals. One of my favorites is acacia trees. Certain species of acacia trees have large hollow growths that hold colonies of ants and the ants live inside and are protected by this growth on the plant and in return the ants will go and will forage in a circle all the way around the plant. Any other predator (any vine or tree or anything) that comes into that zone gets immediately attacked and eaten by the ants, even other animals that might threaten the tree. So there’s this relationship. The tree gives the ants shelter and the ants essentially protect the tree from any competition.

There was even a case recently that I found of a tree that grows in Malaysia called a cempedak tree, and it gets attacked by a fungus that starts to kind of rot the tree a little bit. But it turns out the tree can’t live without that attacking fungus because certain flies (actually midges) come and eat the fungus that’s attacking the tree and in the process they pollinate the tree, they carry pollen from one tree to another. So here’s a case where a tree has adapted to something that’s attacking it and yet it’s turned it into a symbiotic relationship between a plant, a fungus and an animal.

Another interesting example is that of parasites. We have a geologist, Bob Tucker, who goes out to Madagascar a lot to do geological work and you don’t want to have him talk about this at dinner time because he describes these fly larva that get under your skin and they wriggle around and you actually see them moving under your skin. And there are places where there are dry leeches that live in trees and as you walk under it they drop on you and crawl on you. And these are creatures that have found a nice means of living at your expense and parasites are a very efficient way of surviving ecologically.

And of course Ursula talked about sexual attraction and you look at the habits of some animals -- with birds and their songs. My favorite are the mockingbirds that don’t have their own song but copy everybody else’s song and run through a whole repertoire of other bird songs or train whistles or car horns or whatever. And peacock feathers and fish dancing and birds making nests, even humans have very elaborate sort of means of sexual attraction that involve gifts of fauna like fancy dinners (my wife particularly liked Chicago style ribs); flora, gifts of flora (roses) or even minerals, like high pressure phases of carbon (diamonds). Ours is perhaps one of the most elaborate sort of courting/mating techniques.

But it’s incredible to go through this and to see how all of this has evolved originally from one-celled creatures and I’ve seen the power of this in a couple different ways. There was a recent study where someone tried to replicate this on the computer. And what he did was he took a single computer and he created within it a set of programs and these computer programs, they were initially about 50 lines each and all they did was replicate themselves and then erase the parent program so that’s their only job. But what he did was he had them some small random percentage of the time one of the binary digits would be flipped of the program. He essentially put random mutation in the process and just let it crank and let them go and he found over time so many of these ecological techniques were reproduced. Some programs were really small and short and reproduced them quickly and tried to fill up the disk space as much as possible. And some of the programs became longer and longer and had more lines and were just very big and reproduced more slowly. Some of them actually became parasitic and worked themselves into other codes so that when the host replicated itself it actually replicated the parasite program instead. And he didn’t put any of this in there. It just happened on its own using the laws of evolution.

And I do this in my own work. I use something that’s called a genetic algorithm and essentially what I do is let’s say I want to make a map of the structure of the inside of the Earth and I have all these seismograms from all these waves from earthquakes that travel through the Earth. I want to come up with the best picture of the temperature, hot and cold within the Earth. You may remember I showed a map of the slabs at the core-mantle boundary, the sinking lithosphere that had landed, sunk down to the bottom of the mantle. To make that map and ones like it we use this genetic algorithm. And what it does we take some population of models, we start with about 100 models. These are our individual creatures and we write each model out as a strand of DNA essentially. We write out all the numbers in binary code so 1s and 0s. Then we take those and we figure out how each one of these fits the data and the ones that fit very well we give a high ranking and it is more likely to reproduce so we let it reproduce more often and the ones that did a terrible job die off. To reproduce them we take two models and again we have them written out only in binary code and we swap them so this is like sexual mating where the DNA of a child ends up having a combination of two parents. But every sort of hundredth bit or so (it’s a little less than that actually) is allowed to mutate and so there is some randomness that goes into the new children and we go through this whole process and we end up with a new generation and then we repeat the whole process. And what’s remarkable is you can have a very complex model that you’re trying to image and this process of reproduction, mutation and selection will very quickly explore your whole set of possibilities and if it’s a bad possibility it just dies off. But if it’s a good possibility more and more organisms will go there and into that set, that particular model. And this is used in a variety of sciences now and essentially it’s stolen right from life. This wasn’t anything that somebody thought up. We just looked at how efficient life has been in here and we’ve managed to replicate it in doing our work.

Okay, in the last couple minutes I want to show one more slide and this is something called the Drake equation. About 40 years ago a young astronomer by the name of Frank Drake came up with this equation and his goal was to try to find out how many intelligent civilizations you should expect to find in our galaxy. And he wrote it out as a set of probabilities and what he said was let’s take a set of factors and if we multiply them all together (that’s what’s multiplied here, every one of these multiplied by each other) we should get this number N, the number of intelligent civilizations within our galaxy able to communicate. I stuck some numbers in here. They’re gross estimates but they sort of give you an example. The average rate of star formation per year so the number of new stars that are forming each year within our galaxy. The fraction of those stars that have suns that are suitable for planetary system (so maybe 1/10). The fraction of those suns that actually have planetary systems (1/2 maybe). The number of planets that are in a continuously habitable zone. What this means is the number of Earths essentially, the number of planets that are just the right distance from the sun and just the right size. We have one in our solar system so let’s assume each solar system has one. The number of those planets on which life actually originates. There may be certain conditions where for some reason we don’t see, life can’t originate (so we’ll put that as 1/2). The fraction of these planets on which life eventually becomes intelligent. Well, life existed here for a long time before it became intelligent so we’ll make that 1/100. The fraction of intelligent planets that developed a desire to communicate with others. So in other words, how many planets that developed intelligent civilization, how many of those planets do the people want to go and communicate? Well, probably all of them. I mean if you develop intelligence you probably want to find out if somebody else exists in your galaxy so we’ll say all of them. And the average or mean lifetime of a civilization either before it blows itself up with a nuclear bomb or it gets hit by a meteorite impact that kills it all or who knows what. So we’ll pick a number. These are all incredibly unconstrained numbers. You could probably change any one of these by many orders of magnitude but if you just plug in the numbers that I gave you come up with a number that there are 500 intelligent civilizations in our galaxy that want to communicate with us. Actually Drake came up with 10,000 for the number but I couldn’t find his original parameters. Carl Sagan came along and said wait a minute, there are hundreds of millions of galaxies so that means that there could be 10 trillion intelligent civilizations in our known universe that want to talk with us. Well, there’s a problem with this though and actually some recent geologists and paleontologists and astronomers redid some of the calculations and in particular they redid this number here. They didn’t worry about all the rest of this stuff but just this one right here, the number of planets that could be like Earth. And they found out that it turns out this number is probably many, many, many, many orders of magnitude smaller than 1. For instance, our meteorite impacts on our planet would be much, much more frequent and much worse if it weren’t for Jupiter. Jupiter is a big planet that actually, its gravitational field absorbs a lot of incoming meteorites and also deflects a lot of them out into space. So if it weren’t for having Jupiter we’d get zapped all the time. Well, we’ve observed other Jupiter-like planets. The number is over 20 now in other solar systems; however, they’re all bad Jupiters. They are all, all these planets that we’ve seen have widely elliptical, erratic orbits and the problem with that is that would not only fling out meteorites back into space, that would fling us out as well. Our Jupiter is the only good Jupiter that we’ve seen so far that has a fairly circular orbit. All the rest of them, their orbits would not allow small planets like Mercury, Mars, Earth and Venus to exist. We would just get whipped right out of the solar system.

Let’s look at some other factors. Most stars are actually close to the galactic center. However, in that case nearby gravitational pulls from other stars would probably throw trillions of comets in towards any planet. We have huge numbers of comets that orbit outside of our solar system but with other stars nearby these things would get thrown in towards us all the time. We’d have a very high rate of bombardment. Add that to the fact that inside, close to the galactic center there’s intense radiation that Claude talked about, many explosions of large stars. You get larger stars forming because there’s a lot more material. They have shorter lives, they explode as supernovas more frequently and more violently. It’s quite possible that there’s no way that life could live near the galactic center where most of the stars are. So how about at the edges of galaxies? Well, starlight, the spectral composition of starlight from star systems at the edges of galaxies suggest that they tend to be very poor in metal. The stars there much less frequently go through these supernova explosions and they don’t tend to have a lot of rock and metal elements to pull together. And so they just don’t form rocky planets like Earth. There’s very little amounts of silicon, iron, magnesium. You just don’t have the building blocks for planets or for life. Even more importantly, you don’t get the heavier radioactive elements and remember I talked about it’s the radioactivity is the only reason that our Earth isn’t dead. It’s what keeps our plate tectonics running and it’s our plate tectonics that gives us all these wide varieties of ecological niches and that’s important because in a time of catastrophe like a climate change or an impact it’s the life at the fringes that often hangs on and is able to repopulate the planet. If you have one environment you’re going to have a limited number of life-forms, they’ll all get wiped out. Also, it’s the radioactivity that drives the plate tectonics that stabilizes climate by recycling carbon constantly through our atmosphere. Without plate tectonics our planet would swing dramatically in climate, much worse than it ever has. And it also makes dry land, continents. We wouldn’t have land if we didn’t have plate tectonics. That’s not to say that intelligent civilization couldn’t develop in the ocean but ours developed on land so it seems like it might be preferable. What’s worse it seems like there are whole galaxies that are metal poor. Elliptical and irregular galaxies tend to have much lower metal content and therefore are likely unable to sustain life. It only seems like spiral galaxies like our Milky Way and Andromeda tend to be metal rich.

And there are a variety of other factors. Earth has an orbit that keeps it at just the right distance to keep water mostly liquid. Of course it wanders out of that. We do get ice forming but most of our water remains in a liquid phase. Earth also has a moon that’s just the right distance and size to essentially minimize the tilt. Remember I said the tilt on our axis was one of those Milankovitch cycles but it only went from 22½ to 24½ degrees in tilt. That would be much wilder if there wasn’t a moon to gravitationally stabilize it and that’s greatly held down our fluctuations in climate change. And Earth also has just the right amount of carbon dioxide to aid in the development of life but not so much to allow Earth to have a runaway greenhouse effect like superheated Venus has for example. So it seems as if Earth is at just the right size and at just the right distance from just the right kind of star that’s at just the right distance from the center of just the right kind of galaxy. And when you put all those together this number comes down dramatically and these guys proposed it’s quite likely simply on a probabilistic basis of that number that we may be the only planet in our galaxy that can sustain intelligent life.

I have to say that this is sort of out of the realm of science at this point. You almost have to turn to science fiction for the answer to this. One of the first science fiction series or books (space operas as they’re sometimes called) was the Foundation series by Isaac Asimov and he essentially went through this speculation of how humans from Earth would eventually populate the entire galaxy. And in that never once is there any mention of another intelligent species other than humans. After that, with Carl Sagan and Drake talking about all these other types of life-forms science fiction writers kind of scoffed at Asimov and speculative fiction since then always seems to involve other species and often many of them in our galaxy. With these recent results though you have to kind of wonder was Asimov right -- are we alone in the galaxy? These are big questions for which at this point we really have no answers.