Introducción a la biodiversidad, margaritas blancas y negras

Hipótesis de Gaia

El estudio de la habitabilidad planetaria está parcialmente basado en una extrapolación del conocimiento de las condiciones terrestres, ya que actualmente laTierra es el único planeta en el que se conoce la presencia de vida.
La hipótesis de Gaia es un conjunto de modelos científicos de la biosfera en el cual se postula que la vida fomenta y mantiene unas condiciones adecuadas para sí misma, afectando al entorno. Según el de Gaia, la atmósfera y la parte superficial del planeta Tierra se comportan como un todo coherente donde la vida, su componente característico, se encarga de autorregular sus condiciones esenciales tales como la temperatura, composición química y salinidad en el caso de los océanos. Gaia se comportaría como un sistema auto-regulador (que tiende al equilibrio). La teoría fue ideada por el químico James Lovelock en 1961 (aunque publicada en 1979) siendo apoyada y extendida por la bióloga Lynn Margulis.

1

I see the Earth as more than just a mixture of living things and inanimate matter. I see it as a tightly coupled entity where the evolution of the living things and the evolution of the inorganic matter constitute a single and totally inseparable process. It’s a whole system. Somehow or other life appeared on Earth. I don’t give a damn if it was somebody put it here, whether it was a waste bin cast aside by some visiting spacecraft, or whether God fiddled around with the chemicals and started it, or whether it dropped out from space as Fred Hoyle would have us believe. Somehow or other it started here. At that time the Earth must have been just right for a little, otherwise it wouldn’t have survived, but the Earth was evolving geochemically and quite remorselessly towards, although it would take a long time, a state like Mars or Venus, and utterly impossible for life. So life arrived just at the right moment, so to speak. Gaia is the name that I give to the system that is the Earth’s, it’s also the name of the theory of the Earth as a system, which is I suppose saying the same thing in other words.

2

Gaia got its name in the oddest of ways. Many years ago I used to live in a village called Bower Chalke in southern Wiltshire, and a near neighbour of mine was that novelist, William Golding, and he and I were good friends, and we used to go for walks around the village talking about philosophical things and that, and when the idea of Gaia came into my mind – I didn’t call it Gaia then of course – I was telling him about it, how I thought the Earth was a self-regulating system and that the organisms somehow were involved in this process of self-regulation – and he rather liked the idea, and he said to me well, you’d better give it a proper name, so I said what do you suggest? He said I’d call it Gaia, and for twenty minutes we walked on, I was very puzzled because I thought he’d said the word ‘G-Y-R-E’, those great whirls that go round and round in the ocean, and I could see that it was a circular thought that I had in my mind, and I thought ‘gyre’ was going a bit far, and then he suddenly said no, no, no, I meant ‘G-A-I-A’, Gaia, the Greek name for the Earth’s goddess, and of course that I accepted. Voice Over So, how did it all begin?

Para explicar su teoría James Lovelook utiliza  Daysiworld,  un mundo que es orbitado por un sol cuya temperatura está aumentando lentamente. El planeta se siembra con dos variedades diferentes de margaritas como únicas formas de vida: margaritas negras y blancas. ….

Las imágenes siguientes ilustran la hipótesis de James Lovelook, está desordenadas sería capaz de ponerlas en orden?

1

In the early 1960’s Jim Lovelock worked for NASA which steadily grew obsessed with the search for life on Mars. Ten years before the Viking landings in 1976, Jim pointed out that life on Mars would have left its signature in the composition of the Martian atmosphere, and that evidence for such a signature was singularly lacking. The relationship between atmospheric composition and life on Earth led to the first detailed formulation of the Gaia hypothesis; it soon became controversial.
James Lovelock
The old Gaia hypothesis as it was first dated arose like this: what I’d found was that looking at the Earth in the Mars business and discovering this wonderful atmosphere, there were all of these gases out of equilibrium and yet somehow keeping constant, I knew there was something that was regulating it, and it was natural for me to think that it was life that was doing the regulating, and that it was doing it in such a way as to keep the Earth comfortable for itself.

2

I think few would have come upon it differently when confronted with the evidence that I had then, and so the next few years I went chundering around looking for evidence that would support this notion that life was regulating the planet and keeping it comfortable for itself. And I was brought up short and sharp by Richard Dawkins and Ford Doolittle’s comments that there was just no way that life could regulate anything beyond its vena type and this was all nonsense, and this led to the development of the Daisyworld model which showed how in fact it wasn’t life, but the whole system of life tightly coupled with the physics and chemistry of the planet with its environment that did the regulating, with regulating being an emergent property of this tightly coupled system, not something that required purpose or foresight on the part of the organisms. And I think this definitively answered Richard Dawkins’ criticism.

3

I think as another biologist put it even more forcefully than Richard Dawkins, if Gaia is to be real it would require a trades union of the species of organisms to meet annually on Mt. Ararat and negotiate next year’s climate, which is clearly absurd. Now Daisyworld was a model that was made to show that the evolution by natural selection, using all of the selfish gene ideas that Richard Dawkins espouses, could quite naturally, if you coupled the evolution of the organisms tightly with the evolution of their material world, produce a system that was self-regulating; no purpose, no foresight, no planning, was needed. Now the details of Daisyworld are like this. I want you to imagine a model planet just like the Earth orbiting.
Voice Over
Daisyworld is a simple planet. Like the Earth it orbits a star, which like our sun is getting progressively hotter with age. Unlike Earth, Daisyworld has a very simple atmosphere with no greenhouse gases like carbon dioxide to warm it up. And it only has two sets of inhabitants: black daisies and white daisies. The black daisies absorb incoming solar radiation so they warm up, and as they warm up they radiate heat, warming up their surrounding area. The white daisies, on the other hand, reflect the sunlight and stay cool.

4

For both colours of daisies 22.5 Celsius is the optimum temperature for growth. Now let’s see what happens throughout the lifecycle of Daisyworld as things warm up. At first Daisyworld’s young sun is cool and the planet is rather cold, and the heat-absorbing black daisies are at an advantage.
James Lovelock
And consequently by natural selection dark daisies will be favoured, and at the end of the lot, the first season, there will be many more dark daisy seeds left than light coloured ones. So at the start of the next season dark daisies will be off to a head start and soon will be spreading, warming not just themselves but their immediate locality, and then with explosive, positive feedback dark daisies will spread right across the planet and warm it right up to temperatures close to those comfortable for the growth of daisies.

5

Voice Over
The black daisies proliferate and slowly spread out from the warmer equatorial regions until they cover most of Daisyworld, turning it black, so Daisyworld can absorb heat and warm up.
As the temperature gets nearer the 22.5 Celsius optimum for all daisies life gets easier for the white daisies who then prosper. At first they grow best at the warm Equator, then they slowly move out finding a niche alongside the black daisies. But in areas of high solar radiation the white daisies do best as they cool their environment, whereas in areas of low solar radiation black daisies predominate by warming their environment. In all areas the numbers of black compared to white daisies depends on the proportion of heating or cooling necessary to maintain the optimum growth temperature.

6

James Lovelock
I have no doubt that by far the most important thing to come from Daisyworld was the mechanism that it offered to explain how the Earth regulates its temperature. You see, Gaia was not acceptable to most scientists, geochemists, biologists, or anybody else, without a mechanism that explained how it could work. It seemed to them just pure moonshine, nothing solid about it. It was rather like plate tectonics, the theory of vagueness theory. Until a mechanism was available nobody could believe there was anything in it, and the same was true for Gaia, and Daisyworld gave just that mechanism.

1

Voice Over But Daisyworld’s sun is still getting hotter and soon the black daisies find it hard to cope, whilst the white ones stay cool. The white flowers soon outnumber the black ones and Daisyworld becomes whiter and whiter. The white planet can reflect the increasing solar radiation and stay cool, but the sun gets hotter still. Eventually the planet gets too hot and even the white daisies can’t cope. Daisyworld dies.
James Lovelock In a way Daisyworld resembles a living organism. I know biologists hate me for suggesting such a thing, but it does, and perhaps the way in which it most resembles it is that it can die. If the Sun gets too hot for Daisy, the star gets too hot for Daisyworld, then even a total cover with light-coloured daisies is insufficient to keep the planet cool enough for them to survive. And the moment some of them start dying darker, bare ground is exposed, and then again with explosive, positive feedback the temperature zooms upwards, far beyond the range of toleration of any kind of life, so it dies.

2

Voice Over 22.5 Celsius is the optimum growth temperature for both black and white daisies. The black daisies work with the Sun and warm the planet. We call this positive feedback. White daisies work against the Sun and cool the planet. We call this negative feedback. In Daisyworld we’re concerned with the combined effects of both positive and negative feedback. This graph represents the temperature of Daisyworld based on changes in solar luminosity alone, without the influence of the daisies. If we now add the daisies we get this curve which shows both positive feedback from the black daisies, and negative feedback from the white ones. Together they regulate the planet’s temperature, producing a stable environment, despite the changes in solar radiation.

James Lovelock I see Gaia theory as a theory of Evolution in which in no way discards Darwin’s great vision, but includes also the geological evolution of the Earth and couples the two together tightly. What emerges from the synthesis of these two older systems are such properties as self-regulation, that’s to say the regulation of the climate and the chemical composition of the Earth, so that it is always a fit place for life.

3

Voice Over The Daisyworld model is a very general one and you can play all manner of games with it. So let’s make it more realistic by giving the daisies a few problems. For example, we could introduce rabbits to feed on the daisies. At first the rabbits would try to eat up all the daisies but as the daisies became scarcer the rabbits would starve, so the rabbit population would decline as a result. If then the daisy population recovers, this will be followed by a recovery in the rabbit population. This is another example of a positive and negative feedback system which balances out over time. So if the rabbit population fluctuates like this – the daisies correspond like this. During the population cycles there appear to be runaway increases or decreases in the number of rabbits or daisies, but when measured over a long time a balance or equilibrium has been achieved between the number of daisies growing and the number of rabbits supported by them. This balance means that the rabbits have little effect on the long-term wellbeing of Daisyworld. The same long-term balance will eventually be achieved, even if we introduce further biological perturbations. We could, for instance, introduce foxes to prey on the rabbits, or a plague to kill off a high percentage of the daisies, or competition between daisies of different colours, or whatever perturbations we may care to invent.

4

James Lovelock
Biologists’ critics in the early days suggested that if there appeared on Daisyworld a grey-coloured daisy that didn’t use energy making light or dark pigment, it would have an advantage and take over the whole scene, and regulation would collapse; they called this a cheat. I took them seriously and I made a Daisyworld model in which a grey-coloured daisy was included, and to make things harder for the black and white ones I taxed them 5% of their gross rate for making pigment. It was most instructive when the model was run – the dark and light-coloured daisies flourished, just as before; the grey ones flourished as well, although interestingly not quite so well as the dark and light ones. You see it’s really quite simple. When it’s very cold, only dark daisies are fit to grow; light and grey ones cannot. When it’s very hot, only light daisies are fit to grow; the dark and grey ones cannot. So the grey daisies have their place.

5

Voice Over
The effect of feedback is a zone of quite remarkable planetary temperature stability in the face of quite massive changes in solar radiation. As the output of the sun varies, so the black and white daisies simply respond to changing conditions, but in doing so they regulate the temperature. The process is entirely automatic; it’s just an emergent property of the system.
James Lovelock
The most important conclusion I would draw from Daisyworld modelling is that it demonstrates that a system such as Daisyworld can self-regulate without there being any purpose, foresight, or planning, or anything built into the system beforehand that would make it do so. The other most important thing I would single out from it, which I’d add on to that, is that Daisyworld is the mathematical basis of Gaia theory and the explanation of everything that I mean by Gaia.