The way that evolution operates is sometimes grossly misunderstood, so just to make sure that we're talking the same language here's a very quick run down of how it works (It's a surprisingly simple process).
Firstly, let's get one common misconception out of the way. There's a widespread belief that evolution is some sort of deliberate, almost conscious, process or force moving towards a predetermined goal - that birds for instance knowingly developed wings because they fancied doing a spot of flying.
This isn't the case.
You'd be forgiven for thinking that it was the case by the fact that whenever the process of evolution is talked about, even by experts, it's very common for verbs of choice or deliberation to be used, as in phrases such as "Evolution chooses the characteristics that are to be passed on to the next generation." This doesn't mean that evolution purposefully makes a choice by conscious reflection, in the way that you and I make choices. It's a much more inert use of the verb to choose - think of it more like the way that we say that a river chooses its route to the sea. Rivers obviously have no say whatsoever in deciding their courses - the flow of their water is simply channelled down the steepest available gradients of the landscape. Indeed it may be a good idea to ditch the concept of choice when it comes to evolution, and to borrow from the river metaphor instead - to say that evolution is channelled along the route that it takes (dependant on the ecological "landscape" that's around it at the time).
Here's how this channelling takes place.
When a creature has offspring, those offspring all vary very slightly in quite random ways, such as by being slightly different colours, different sizes and so on. Some of these offspring, purely by chance, will be better suited for survival in their particular environment. For instance, by being a different colour they may blend in with their surroundings better and thus be less likely to be seen, and then eaten, by a predator. These offspring will thus be more likely to survive and have their own offspring - which will on average have inherited the same fortunate variation that improved the survival chances of the parent. Thus the trait will be passed on to further generations.
This process by which such random advantageous characteristics are passed on from generation to generation is known as natural selection.
(Charles Darwin, who coined the phrase natural selection, was actually slightly unhappy with the term, as he felt that some people may think that it implied deliberate, conscious selection rather than the purely automatic process that he intended. How right he was.) Let's look at a few examples of the process in action to get a better idea of how it works.
Imagine an animal that lives in a very cool, though not freezing cold, sub-Arctic climate. Say a type of fox.
The climate's pretty nippy, but the fox has fur, so it survives quite comfortably.
Gradually, over a very long period of time (quite a few fox generations) the climate changes as the earth moves into one of its periodic ice ages. The fox's world gets noticeably colder and harsher.
Amazingly, as the climate gradually cools, successive generations of fox are seen to sport longer and thicker fur that helps to keep them warm. The foxes' coats get longer almost in step with the cooling climate. This looks very much as though the foxes have decided to grow more fur to suit the new conditions.
But it isn't so.
Here's what really happens.
Whenever a fox has a litter of cubs each cub will inevitably be physically slightly different from the others. Some will be larger, some smaller, some stronger, some weaker, some darker, some lighter, some more furry, some less furry, and so on. Imagine that a pair of foxes has a litter of three cubs: one that's more furry than its parents, one with the same amount of fur as its parents, and one with less fur than its parents. On average, that's exactly the fur-length distribution that you'd get in a typical sample of three fox cubs.
These three cubs are born into a world that's slightly colder than the one that their parents were born into. The cub that has less fur than its parents finds the conditions too harsh, and dies of hypothermia. The other two cubs survive. However the cub that has the same amount of fur as its parents finds the going tough in the cold, so it grows up to be a less than perfectly healthy specimen within foxdom. The third cub - the one with the most fur - survives quite well because it is adequately insulated from the cold. This cub grows and thrives. It mates with another fox that has thrived (which quite probably also had slightly more fur than its parents). The resulting cubs produced by this coupling will have similar traits to their parents - though as usual with minor variations, including a variation in the density of their fur. Imagine that this pair had a litter of three cubs, just as described for the parents above: one that's more furry than its parents, one with the same amount of fur as its parents, and one with less fur than its parents. If these cubs were born into a world that was continuing to cool down the cub that would be most likely to survive would be the one with the thickest fur. This cub is slightly more furry than its parents, and is noticeably more furry than its grandparents. So it is, that if the furriest offspring of each generation are the ones that survive, the whole species becomes more furry in small steps.
It's important to realise that the survival of any individual fox is purely the luck of whether or not its characteristics mesh well with the prevailing conditions. I have just described the scenario in which the fox cub with the thickest fur survived as the climate cooled: however if exactly the same three cubs had been born at a time when the climate was warming up instead, the fox cub with the least fur would have been the most likely one to have survived (as its more thickly furred siblings would have found their own stifling coats a hindrance, just as you yourself find a thick coat a burden on a hot day).
In the example above the reason that the foxes evolved to have a different thickness of fur was a change in the climate. Climatic challenges such as this are however just one of the pressures on creatures that results in their changing or evolving. Another pressure is the threat posed by other creatures that want to make a meal of them.
The advisability of avoiding being eaten was the pressure that, amongst other things, made some creatures develop colouring and patterns that serve to make them merge into their backgrounds, effectively camouflaging them (as I mentioned briefly above). Figure 51 shows a moth that merges with the bark of a tree so well that you can hardly notice it (I know this photo is reproduced in shades of gray, but believe me, the effect is practically the same in the colour version, which is essentially the same but in shades of brown).
How is it possible for such an incredible congruity of colouring to come about? Figure 52 on the following page shows a representation of two moths resting on the bark of a tree. The moths are both the same colour and are slightly lighter than the bark, allowing you to see them. The moths aren't particularly well camouflaged, but fortunately they survive long enough to mate and lay eggs, which eventually turn into more moths.
As with almost all of nature, each of these resulting sibling moths is physically slightly different due to genetic variations. Some are larger, some are smaller, some have longer antennae, some have shorter antennae and so on. Some of them are slightly different colours. Of the parent moths' many offspring let's pick three that are different colours, as shown in Figure 53, and look at them more closely.
The centre moth of the chosen three is exactly the same colour as the parent moths, while one is slightly lighter and the other is slightly darker.
These moths spend most of their time resting on the bark of trees that are the same as the one that their parents rested on, with bark of the same colour. Because each of the moths is a slightly different colour some are easier to see on the tree bark than others.
Unfortunately, the easier it is for a moth to be seen, the more likely it is to be eaten by a passing predator that's on the lookout for a meal. If a moth is eaten by a predator before it manages to breed its characteristics aren't passed on to the next generation of moths. In the figure above it's a fair bet that the moth on the left, the lightest one, would be the most likely to be seen, as it is noticeably lighter than the background on which it sits, and is therefore the most likely to be picked off by a predator. The middle moth (which is the same colour as its parents) is also quite light, and thus has more than a passing chance of becoming a predator's meal at some point, but it might make it to mating age if it's lucky (as its parents were).
The right hand, darkest moth from the trio is more likely to go undetected by predators because it's closer in colour to the tree bark, and thus it's got a much greater chance of surviving long enough to breed.
The offspring of this darker moth will tend to inherit the moth's characteristics, so they will tend to be slightly darker than the average of the parent's generation. Figure 54 shows a small representative sample of the offspring of this moth, all sitting on the bark of the same tree. You may notice that on average they are closer in colour to the tree bark than the moths that featured in Figure 53 above, because their parent was closer to the colour of the tree bark. But they nevertheless vary in colour. Some of the offspring are lighter than the parent, others are the same colour as the parent and others are darker.
As in the previous figure, one of the offspring in this figure is less likely to be eaten by predators than the others.
Imagine that you are a predator that eats moths (perhaps a bird of some kind, or a small child) - which one of the moths in this figure do you think you'd be least likely to notice (and thus least likely to eat)? It's not too difficult to decide: the moth that you'd be least likely to eat, and which thus would be the most likely to survive and have offspring, is - yes - the middle one.
You may now be asking "What does he mean, the middle one? There is no middle one." But that's where you're wrong: there is indeed a middle one, as you can see if you look at Figure 55 on the next page.
This is the same figure as the previous one, except that it's had the colour of the tree bark removed.
The reason you didn't realise that there was a middle moth was because it is exactly the same colour as the tree bark on which it's resting. You overlooked it for the same reason that a predator would have overlooked it too.
Because of the fact that this moth is much less likely to be eaten by a predator than its siblings it's much more likely to survive and to breed, producing offspring that are likely to be a similar colour to itself (though, as always, not all identical).
A sample of the offspring of this moth are shown in Figure 56. As you can see, although the average colour is the same as that of the parent (the centre, invisible offspring), some are lighter and some are darker. As in the previous examples, the lighter moths are visible against the tree bark and are thus likely to be predated. But now the darker offspring are darker than the tree bark, and are thus also visible - and are therefore likely to be predated too. Once the moths' colour matches that of the tree bark it's no longer an advantage to be darker than your siblings: a state of equilibrium is arrived at, where variation in either direction is a handicap. As a result the moth species stablises at the colour of the tree bark.
So it is that the characteristic of camouflage that the moths exhibit is arrived at purely as a result of normal variations in colouring between offspring.
This is a nice example of natural selection at work because in one way the moth that is most likely to survive to breed another day is specifically the moth that is not deliberately selected for anything (In this case not being selected to be a meal for a predator). The reason that the predator doesn't select this moth is exactly the same reason that you didn't select it when I asked you to pick the most likely contender for survival in Figure 54. How could you (or the predator) select something when you didn't know that it was there? (If you did select the middle moth in Figure 54, perhaps because you saw through my ploy, you're cleverer than the average predator.) The same applies to the moth in the centre of Figure 55.
This process of not selecting something because you don't know that it's there will come up again later in the book, in significantly different circumstances.
You can see from this process that the moths don't deliberately choose their colour so that they are camouflaged. In fact it's quite possible to imagine a species of moth in which the moths are blind (perhaps finding their way around by using some sense other than vision, such as echo-location or smell) and that are thus totally unaware of their own colouration - yet they could still evolve perfect visual camouflage in exactly the same way, due to the fact that predators would eat the least well camouflaged specimens.
Although evolution is normally thought of as being a glacially slow process, with small changes in the features of creatures accreting over vast tracts of time, you can actually see the process of natural selection at work with your own eyes if you look in the right places.
An example involving the colour of moths, as described above, was famously observed in the industrial north of England in the mid twentieth century. Before the 1950s there was a lot of air pollution in the region that made the trunks of trees very dark with grime. A species of moth, the peppered moth, lived on these trees. The moths were dark and were very effectively camouflaged, matching the grimy bark on the trees perfectly, making them difficult for birds and other predators to detect. During the 1950s the air pollution in the area dropped due to changes in industrial practice and the grime on the trees disappeared, making the trees lighter in colour. This made the dark peppered moths stand out against the trees. Within a few years all of the peppered moths that lived on the trees were lighter in colour, perfectly matching the newly pristine bark.
(This example of evolution in action fell into disrepute in 1999, due to a reported inaccuracy in the data collecting method of the research. The research was discredited to the extent that it was even dropped from school textbooks. However the reported flaws in the methodology were gross exaggerations by interested parties, and the accusation of inaccuracy has since been rescinded. The research, which was carried out by Bernard Kettlewell, was indeed valid.) A few years ago I was reminded of the evolutionary dynamic that was at work with these moths when I observed a similar process at work in my garden pond. While peering into the water I observed part of the same plot being acted out, except that in this case the players were fish.
The pond at one time had five small ornamental carp in it. They were all exactly the same in every way, except that four were golden in colour (large goldfish in fact), while the fifth was almost black.
A few months after the fish had been introduced to the pond I realised that one of the goldfish was missing: a heron or other bird had perhaps taken it as a meal.
Within weeks there was not a single fish to be seen in the pond. The bird that had taken the first fish had probably been back for the rest.
I thought no more on the matter until many months later, when one particularly sunny and warm day I sat by the pond side and relaxed by gazing down at the now fish-free water. Suddenly, a movement in the rather dark water caught my eye, and to my surprise I saw the black fish swimming just below the water's surface.
This dark fish had survived for months, avoiding detection by predatory birds (and by me). It had remained unnoticed while its showy golden relatives had been plucked from the water one by one, betrayed by the glint of light on their bright scales.
If there had been a male and a female dark fish in my pond, along with male and female gold fish - allowing breeding to take place - the pond would eventually have become stocked with nothing but dark fish, with no golden ones at all.
(Brightly coloured goldfish do not exist in the wild, because they would instantly become meals for predators. They are the result of selective breeding by man, in unnatural environments. Normal wild carp have a tendency to have a few golden scales amongst their usual duller ones, and it was as a result of people deliberately choosing to breed from the fish that had the most golden scales that goldfish arose. The process could be termed evolution by unnatural selection.) I hope that's quashed any ideas about the deliberateness of the process of evolution.
There's another aspect of evolution that's frequently misunderstood too. This particular misunderstanding revolves around the phrase "the survival of the fittest" - a phrase coined by the nineteenth century philosopher Herbert Spencer. This phrase is often misinterpreted as meaning "survival of the strongest", while in fact it more accurately means "survival of the most appropriate", as the word "fittest" in this context means "most fitting". You just have to look at the cases of the moth and the fish above to see this point perfectly illustrated: the members of the species that survived did so because of a quality that was nothing to do with physical strength at all - colour variation.
In fact it's easy to imagine scenarios in which supposedly "superior" physical qualities such as greater strength or size can actually be a handicap.
Imagine, for instance, two penguins walking across very thin ice. One penguin is big and strong, while the other is smaller and altogether weedier. Which penguin is most likely to make the ice break under its weight, thus falling through into the sea below and ending up in the jaws of a leopard seal or killer whale? Yes, the big strong one. In this case survival of the lightest would be an appropriate phrase.
Thus it is that not all creatures are big and strong like lions, but some are small, light and relatively weedy like mice.
So there you are. That's how evolution works, in a very small nutshell.
That explains briefly how evolution can account for the physical features of living things, such as their colour, size and so on. But how can the process of evolution explain the existence of non-physical qualities such as the one that we're concerned with now - awareness?
Here, in the next chapter, is a possible route.
