Life from non-life had to happen exactly once, and then natural selection takes over from there. Natural selection is always painted as a random process over long periods of time by creationists, but that's either a complete misunderstanding or an outright lie. It's true that random mutations are the catalyst for change, but if that mutation conveys a tangible benefit, those with the mutation usually live longer, breed faster and more often, and have a population that will eventually dwarf those who do not have the beneficial mutation. This is because population growth is exponential, i.e., roughly Population = e^{rt} (2.7128.... to the rt th power), and is extremely sensitive to the value of r, which is the rate at which a population breeds.
If you want a reason why population growth is exponential, look at this example discussing ant populations (in you can view the emigration term
a as the death rate, and always set it greater than or equal to zero since it's not possible for a negative number of ants to die).
quick explanation of population modeling (see the section called
Class work on a project)
http://ocw.mit.edu/NR/rdonlyres/DA05...104E/0/r01.pdf
solution showing pop growth as exponential
http://ocw.mit.edu/NR/rdonlyres/AA67...3/0/r01sol.pdf
Check the graph I posted below of two functions e^2.0t and e^1.9t. r=2.0 is the breeding rate of something with a beneficial mutation, and r=1.9 the rate of that species without the mutation [so we can say the mutation provides about a 5% = ((2.0-1.9)/2.0) * (100%/1) benefit ion breeding rate]. I know the numbers 2.0 and 1.9 for the growth rates may seem a bit artificial, but every set of two exponential functions e^rt, e^st with 0<r<s behave exactly in the same way very quickly.
Anyways, in the image below, the black lines are the graphs of e^2.0t and e^1.9t, with e^2.0t (the graph of the population with the beneficial mutation) as the graph on the left, and e^1.9t on the right. The blue lines represent the difference between the two populations at a time of say 32.2 units of time (could be years, or roughly generations... whichever time scale one uses, the rate will have to be adjusted accordingly, since of course more will be born in a year at the same birth rate than in a month). Notice it's pretty substantially favoring the population with the beneficial mutation. However, if you go just about 0.2 time units longer (to 32.4 time units), you can see the difference in population between those with the mutation and without is much larger than before (it is shown by the green lines), and that e^2.0t continues to become way larger than e^1.9t. In fact, the ratio e^2.0t/e^1.9t (=e^0.1t) will grow very quickly to infinity as t grows, which is the same as saying the population with the beneficial mutation will reasonably quickly dwarf the population without the mutation.
As an example, a primitive wing might help an animal that lives in trees to slow his fall when he jumps down to grab prey on the ground, whereas one without that proto wing might be injured or killed by the fall. The animal with the proto-wing therefore has a huge advantage in that he can watch his prey from above where he has a much broader view of his hunting grounds and he can jump down to quickly pursue any prey he finds. His compe or without the mutation must either hunt from ground level (and thus not see as many opportunities) or climb down the tree before he can begin his pursuit of what he does see (thus giving extra time for the prey to escape). It's pretty easy to see the animal with the proto-wing is going to be far more successful a hunter, and thus will spend less time, less energy, and will have a lower opportunity cost for his hunt (leaving him more time to go out and get laid and pass his genes on). He's also much more likely to live longer, since he can be a much more successful hunter.
The proto-wing doesn't allow him to fly or to even glide, but it clearly provides benefit that will almost certainly become selected for his species (by the argument above about population growth being exponential). In this way we see that an animal can quickly derive great benefit from a wing-like appendage even if it doesn't provide the ability to fly, and that having a wing doesn't have to be an all or nothing state. Clearly, a wing is not an example of irreducible complexity.
Same with the eye. No one thinks an eye was just mutated all at once. You don't need cones to tell there's a light source (only rods). An extremely primitive eye may not let one see colors or long distances, but it can still be useful for telling if something runs across your path or if one is about to walk off the side of a cliff the same way that someone with cataracts is still better off than Stevie Wonder. The eye as we know it today is clearly not an example of irreducible complexity.
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