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| Possibly a white-morph peppered moth or a light coloured marbled moth |
Let me tell you a story,
The peppered moth was usually white with black flecks like the moth featured above. Moths of this colour blended in with the lichen & bark of the trees they sit on during the day which reduces the ability of birds and other predators to find and eat them. Then the industrial revolution came to Britain, the smoke from the coal-powered everything killed the lichens and stained the trees black.
Some peppered moths are completely black, these moths before the industrial revolution were rare because most were eaten quickly after emerging as adults. After the industrial revolution these black moths were harder to see against the blackened trees so they survived and reproduced generation more black moths. White moths were quickly eaten leaving only a few lucky ones to reproduce.
After passing a Clean Air Act, the air pollution began to decrease and the trees returned to a more white state. The few white moths were now camouflaged and were not eaten restoring the numbers of white-type moths while the black-type were eaten.
This is a biology-classic as well known among anyone who has taken a class in evolution as Shakespeare or Dickens is to those who have studied literature.
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I find it quite bizarre that people find evolution a hard concept to grasp. Through the years since its discovery/formulation, many have explained it eloquently and simply. But my preferred formulation won't be found in any textbook or lecture theatre (not yet at least) because it is a tautology:
Whatever continues to exist, continues to exist.
- Me.
That is it. One single tautological statement sums up a theory which underlies all of modern biology and has even been lent to other fields such as sociology, and physics.
But perhaps I should clarify. All things we observe today exist and are able to be observed because they have managed, either through luck or because of some property(ies) they possess, to continue to exist since they arose. If it is through luck we call it "drift", if it is through properties they possess we call it "selection".
There are two ways to persist: 1) survive or 2) reproduce. In the long run statistically the survival strategy will fail. Whether it is a lightning strike, a hungry predator or a volcanic eruption eventually something will kill/destroy every individual. Thus the only feasible long term strategy includes reproduction.
Evolution by natural selection is the inevitable consequence of any method of reproduction with high but not perfect fidelity, (Note: 100% perfect reproduction is impossible because of randomness at the quantum level), since not all possible variants which could be produced from the mistakes in the reproductive process will have the same ability to persist.
The advantage of thinking about Evolution in terms of my tautology is the intuitive lack of agency which distinguishes Evolution from the various incarnations of Creationism/Intelligent Design. Whatever continues to exist, continues to exist. It doesn't matter how it continues to exist (some truly horrifying/cruel things have evolved, like-wise many beautiful/altruistic things have evolved), nor is there a plan or intention for what should or should not continue to exist. Likewise there is no planning for the future, evolution can and frequently does fail to occur resulting in species going extinct.
Similarly my tautology also avoids the trap many people fall into of expecting everything to be perfectly suited to its environment. Organisms do not have to be perfectly suited to their current or past environments they just need to be "good enough" to continue to exist. This means, particularly when it comes to behaviour, that quick and dirty patterns or rules (aka heuristics) are be common. As long as the rule works more often than not it will on average improve the organism's ability to survive & reproduce (fitness) thus continue to exist in the population. The consequences of this are often hilarious, such as between species sex, or animals getting drunk, or moths and other insects flying into lights.
Meanwhile, long lived organisms such as trees can persist through survival long after a competitor starts out-competing them and slowing pushing them back until conditions change to give them the advantage again (eg. oaks vs beech). Organisms in remote habitats with little competition don't need to be as well adapted as organisms in highly competitive habitats (eg. Australian/New Zealand endemic species).
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Evolution Perspectives
It is important to note that my tautology does not specify the units it applies to. Whether you are looking at genes, organisms, or ecosystems whatever continues to exist, continues to exist. The major source of continuing controversy in the study of evolution is the correct scale or viewpoint is most relevant or correct. Darwin's Origin of Species focused on the level of the individual organism, patterns of traits change over time in a population in response to the survival and reproduction of organisms. Since the flourishing of molecular biology the current understanding now favours Dawkins' Selfish Gene perspective, where individual genes are the units of selection and frequencies of alleles (different versions of the same gene) change over time in a population in response to the survival and reproduction of the alleles themselves. However, behavioural scientists/psychologists often argue for a group-based perspective where the growth and success of one group vs another group results in genetic and trait changes across the whole species. Even beyond, some ecologists suggest an evolutionary perspective at the ecosystem level where populations and characteristics of different species within the ecosystem change in response to natural selection.
Using mathematical models it has been shown that the group perspective to too weak (because it is indirect and groups are made of mixtures of genes & traits) to be of general importance to evolution. Likewise, ecosystems will obey the whatever continues to exist, continues to exist tautology can be considered as being under natural selection but they change too slowly to have significant influence on the genetics and traits of individual species. However, the individual vs gene perspective debate continues despite the success of the gene perspective's triumph in explaining altruistic behaviour because of the emerging complexity of the relationships between genes and the traits possessed by the individual. Even Lamarck, long ridiculed by geneticists as being misguided, is being revisited since the uncovering of epigenetics.
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A word to the Creationists
In case some creationists accidentally find this page, I shall give a brief response to the common issues they raise:
1) The evolution you explain is only within an existing species. True, I have not addressed the origin of species or life in the above I have only argued that once in existence all thing must follow my tautology. However, the organic chemistry which underlies life comes in two flavours (right & left isomers) and all life we know of uses the "left" kind. In addition, all cellular life (exclude viruses) uses DNA as it heritable information which is translated into proteins (made of the same 20 or so amino acids) using the same 3 letter code (with one or two exceptions) despite the fact that millions of such codes are possible. Many of the molecular machines involved in this process are remarkably similar across all organisms. All of which indicate a single origin of all living things on Earth, after which whatever continues to exist, continues to exist is all that is necessarily to reach the current state.
2) But you can't prove there isn't a creator. I can't prove there isn't a pink elephant living on the moon either but it is safe to assume there isn't one. But for argument's sake let's entertain the "Creator Hypothesis" (Note: even if a creator exists it is equally likely to be Zeus or Odin as the Judeo-Christian god) what can biology tell us about this creator? Given the points made in (1) we have to conclude the creator is lazy. Given the mistakes mentioned at the end of section two we must infer the creator is also stupid or error prone. And given the horrors of anthrax, ebola, and many parasitic wasps/fungi we must accept the creator is either sadistic or inattentive. And given the relative numbers and total mass we must conclude the creator cares much more for insects (such as moths) and bacteria than human beings. Frankly, I'm glad there isn't a shred of evidence in support of the existence of a creator.
