Most creationist arguments can be summarised as "complexity, complexity, complexity - therefore god"
We have all heard the illustrations about the odds of (insert favourite example) evolving, being less than 10,000 monkeys typing Macbeth by pure chance.
Evolution is not like that.
The genius of Charles Darwin was in recognising the power of natural selection as an accumulator of small random changes.
Imagine our 10,000 monkeys randomly typing until one of them by pure chance comes up with "When.."
At that point all the other pages are scrapped and every monkey is given a copy of this page. We observe some more until another monkey adds "shall.." and so on through thousands of iterations. How long would it take to achieve "When shall we three meet again? In thunder, lightning, or in rain?" Completing the full play now becomes inevitable.
Evolution is a little bit like that.
The changes in the genome are random - the selection of useful changes is not.
The illustration is also misleading because it assumes there is an end product that we are hoping to achieve. This is sometimes referred to as the teleological fallacy. Evolution had no purpose in mind. It isn't trying to produce Macbeth or build a human. Whatever works is favoured by natural selection - from bacteria to beetles, it doesn't care.
We can illustrate the power of natural selection acting on random mutations with a very simple example - the ability to see ultraviolet light.
The list of birds that can see ultraviolet is a very random collection of species including the Zebra Finch, Herring Gull, Starling, Rhea and Budgerigar. Anders Ödeen, an animal ecologist at Uppsala University in Sweden mapped the relationships and concluded that the ability to see ultraviolet has evolved separately at least 14 times.
There are a number of advantages of seeing UV. Blue Tits hunt caterpillars that are camouflaged with visible colours. Kestrels can hunt voles by seeing the UV reflected from their scent markings. The rim of the mouths of chicks from at least eight species of bird are highly reflective in the UV band. Parents returning to the nest pay more attention to those with the strongest UV markings.
Sexual preference also seems to play an important role in the selection for UV features. The feathers on the crown of the male Blue Tit are UV reflective. In laboratory experiments females preferred males with the best markings. When sunscreen was applied to the head and neck of a male it was unable to attract a mate - please don't try this at home.
Didn't see that coming..
So how do birds evolve the ability to switch from violet to ultraviolet vision?
The difference is really simple. The gene responsible for the change is the SWS opsin gene that we mentioned in the previous thread...
In birds who see the world in a similar way to humans the protein has the amino acid serine at position 90. This is coded for by the three letters (or codon) "AGC" at letters 268-270 of the gene.
In birds who see UV light the first letter has been changed through a point mutation to "TGC" which produces the amino acid cysteine. This single substitution slightly changes the physical shape of the protein molecule changing its sensitivity from violet light with wavelengths of 405 nm to ultraviolet at 360-370 nm.
So let's look at the maths and see how both random mutations and non-random selection has shaped the visual world of birds.
Random Mutation
The genomes of every animal, from fish to humans, experience copying errors at a predictable rate of 1 per 500 million bases of DNA. Since animals have two copies of most genes it takes on average 250 million offspring before any particular letter of code gets changed to a different one.
Remember that DNA is made up of four letters so that "A" is equally likely to get switched to T, C or G. That means that one out of every three mutations will change our "AGC" to "TGC" and confer UV vision - once in every 750 million offspring.
To see how long will it take for this useful mutation to occur in a species we can take Herring Gulls as an example. These "rats with wings" breed once a year, and long-term population studies suggest that one million chicks per season is a conservative estimate. The result is that a switch from serine to cysteine will arise every 750 years. Of course not every genetic lottery winner goes on to leave offspring, they might get eaten by a predator or fall out the nest. We need to think in terms of the long periods of time that evolution has available. In 15,000 years - a blink in evolutionary terms - the UV mutation will have occurred at least 20 separate times and in a million years 1,200 times.
Non-Random Selection
Mutations result in different varieties of genes. DNA consists of four letters, so each of the three letters in our codon "AGC" can be changed into any of the other three letters by a point mutation making a total of 9 new combinations.
If evolution was all about random chance then we would expect to find all of these variations in equal amount in the natural world.
This is where natural selection comes in.
There are three possible fates for new varieties - or "alleles" - of genes. If a mutation affects survival or reproductive success positively then they will be favoured by natural selection and become more common in the gene pool. If they make their host less able to survive and reproduce they will be eliminated. If they have a neutral effect the proportion of old and new alleles will drift according to random fluctuations.
A study of 45 species of bird species from 35 different families revealed that every one of them without exception had either "AGC" or "TGC" at letters 268-270 of the SWS opsin gene. Just like the manuscripts being produced by the 10,000 monkeys all the other versions had been rooted out by natural selection.
We will return to this theme of the power of natural selection to accumulate useful changes in future threads.
Evolution is a Fact - Index #1-20
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Evolution is a Fact #21 - Footprints in the Sand
Footprints at Laetoli show our Australopithecus afarensis ancestors were bipedal 3.6 million years ago.
Evolution is a Fact #22 - The Hillocks of Hiss
A vestigial feature if the human ear shared by 10% of the population demonstrates our evolutionary history.
Evolution is a Fact #23 - Faunal Succession
The consistent sequence of fossils found in the rocks can only be explained by evolution.
Evolution is a Fact #24 - The Origin of Your Inner Ear
How the bones that reptiles eat with became the bones that we hear with.
Evolution is a Fact #25 - Deep Time
Scottish geologist Andrew Hutton discovered the proof of earth's great antiquity.
Evolution is a Fact #26 - Colour Vision
How gene duplication - new "information" -and mutation equipped us with trichromatic vision.