Darwin’s great breakthrough was that of finding the only one explanation of the great variety and complexity we find in the living world, which is compatible with the fact that the matter and energy of which living beings are made of can only do what they do because of purely physical mechanisms. There is only one type of cause capable of making a particle to move from one place to another: the forces (mainly electromagnetic and gravitational) exerted by the other particles surrounding it. ‘Finality’, understood as a different kind of cause from mere physical forces that move both atoms and snakes is simply and plainly a fiction that cannot have any real causal role in natural processes.
The important point about Darwin, hence, is not that he proved that biological evolution obeys no finality at all, but that he made coherent for the first time the vision of mater and energy that modern science was developing, with the fact that biological processes undoubtedly looked like if they were obeying some kind of teleology. His explanation is for us nearly trivial (as it was for many of his contemporaries, who complained that something so simple and obvious hadn’t occurred to them in the first place), and it consists, of course, in the thesis of modification with adaptation thanks to natural selection and random change.
Unfortunately, the idea that finality is a kind of intrinsic natural (or supernatural) force, different from ‘physical’ causes (in the sense of those studied in physics), that is, the idea that history, including natural history, can and must be interpreted in terms of finality and progress, is so deeply entrenched in our monkeyish brains, that one century and a half of Darwinism has been incapable of convincing many people of the (for others, obvious) truth that biological processes lack (irreducibly) teleological causes. The efforts of many scientists and philosophers have been devoted, hence, to trying to find something like an ‘occult teleology’ in the Darwinian mechanistic universe. But this is just a dream, a way of disguising with apparently profound words the crude Darwinian reality of which I shall try to persuade you once and for all.
Rejecting that the history of the universe, or the history of life, respond to an aim is not the same, however, that denying that within nature there can exist something appropriately called ends, aims or goals. Our own desires, by the way, are goals, obviously: I am now carrying out the activity of pushing a computer keys because I have the goal of writing an article, and I am as a legitimate a part of nature as a waterfall or a solar flare can be. So, if I have ends or goals, and I am a part of nature, it necessarily follows that there are, within nature, some goals or ends (i.e., mine own ones), and the same happens with the goals of other people and even of other animals, for the capacity of desiring and orienting one’s behaviour to those desires is surely much older than the genus homo. Denying that evolution has a goal is not equivalent, either, to reject that biological processes and organs can be understood in a functional sense. There is no problem in asserting things like that the birds’ wings have the function of allowing them to fly, for example. The only thing we need to take into account is that modern evolutionary biology does not make something as bizarre as assuming that living beings possess a kind of ‘immaterial essence’ or ‘entelechy’ that ‘pulls’ from their organs during their development in order that they develop as they should, i.e., with the ‘goal’ of reaching his ‘optimal’ form, or something like that. No, the growth of organisms is ‘pushed’ for physical causal processes that take place in a totally scrupulous way forward, from past to future, not from (an ideal) future to past. All chemical reactions that happen within a living being are processes in which no physical law is violated, processes in which the physical state of the system at a precise moment determines (statistically, at least) the state of the system in the following instant, and there is nothing like a ‘final goal’ that has any causal role in those processes. The only thing we are saying by using the functional vocabulary in contexts like these ones is that the past evolutionary history of those organisms resulted, in a non-teleological way, in a system containing enough information for the processes occurring in the way they are taking place, instead of another way.
Hence, nature contains goals and aims (functions, desires…), but these ends are the products of the evolutionary process, they are a result of evolution, they are not the cause of evolution. The causes of evolution are just the physical, non-teleological laws that describe the behaviour of every particle, field or atom in the universe. These laws determine that given certain circumstances (e.g., chemical systems capable of creating copies of themselves with higher or lower fidelity, and in higher or lower numbers), there is a big chance that some systems will be formed that might be understood in teleological terms. Let’s think how absurd it will be to confuse cause and effect in other analogous cases. For example, digestion and respiration are also processes created by evolution: there was nothing that might be called ‘digestion’ nor ‘respiration’ before there were living beings. But thinking that evolution itself might be caused, or propelled, or governed, by ‘a digestive process’, would be utterly absurd. Digestion, respiration, no less nor more than functional adaptation or conscious volition, are just parts and results of that big process we call ‘evolution’, they are different parts of its result, not a kind of cause imposed to nature ‘from above’ or ‘from inside’ (at least in the sense of something qualitatively different from its own physical mechanisms). Evolution must take place first in order that something like teleology appears.
It is because of that that it is completely absurd to think that biological evolution can be intrinsically understood in terms of ‘progress’. Of course, as in the case of any other natural process, we must apply to it some of our values (created by evolution) and discuss whether the process has led or will lead to some ‘improvement’ in terms of those values. For example, we might think that crystals have a higher aesthetic value than liquids or than the chemical suspensions from which they arise, and we might say, hence, that the process of creation of crystals in nature entails ‘aesthetic progress’. But the process in itself cares little whether its final product accords more or less with our own aesthetic values. The essential point is that what we are calling ‘values’ here, is just another (non-teleological) result of a natural process, they are just a peculiar feature of our own biology as human beings. This does not mean that your values, the values you happen to have, are ‘genetically determined’, or something like that, for our genetics just makes that our organisms develop in one way in certain environment and in different ways in other environments, and so, the same genes might have you made to have different values if you had been raised in a different place or time, or if you had happened to have different experiences. These ‘experiences’, these ‘environments’, these ‘other places or times’, are, in their turn, nothing else than different combinations of physical fields and particles interacting amongst themselves. In a nutshell, having the values you have is, again, a result of an evolutionary process, not its cause.