Let's unpack what you're asking. You are requesting me to provide evidence for how only the final product (i.e. primitive sight) is advantegous, and not the countless iterations of random mutations without sight that had to precede it. In the scientific spirit of not only relying on common sense, I am happy to humour you.
There is little doubt to any party to these debates that sight (even primitive sight like that of a unicellular eyespot) is advantagous. Where the evidence is lacking is precisely in the accounting for the exact nature and mechanism whereby these tiny mutated iterations (which is the way how natural genetic mutations work) towards such a seeing organelle were each consistently advantagous as a random process. And that this random process more or less accurately predicts the time-frame of the evolution of the eye as observed in available evidence. The onus to provide such evidence is on the claimant of successive and consistent iterations of advantagous random mutations
. The onus is not on the skeptic of such a claim to prove that this is not the case. Empirically we know most mutations are disadvantagous. Take fruit flies for an example:
A 2007 study on genetic variations
between different species
suggested that, if a mutation changes a protein
produced by a gene, the result is likely to be harmful, with an estimated 70% of amino acid polymorphisms
that have damaging effects, and the remainder being either neutral or marginally beneficial.
Thus, rather than being uniform, the random distribution of mutations would, in light of empirical evidence, most probably be skewed in the direction of unfavourability. Moreover, on a purely logical account, what we know as extant and therefore selection-wise advantagous biological species represents a limited number of specific configurations, whereas there's an infinite number of logically possible phenotypical configurations caused by genetic mutation that are disadvantagous.
And it's this point that brings us back to the actual issue, which is the zero mathematical probability of any finite iterations of random genetic mutations of a simpler configuration to generate a more complex advantagous configuration out of an infinite range of possible disadvantagous configurations and a finite range of advantagous ones. Any number divided by infinity is a zero. In other words, any argument/model that appeals to random mutation cannot predict (account for) observable evolution within the last 600 million years, unless
it either (1) limits the possible configurations for random experimentation to be (sufficiently) finite, or alternatively (2) allows for an infinite range of random experimentations to have already occurred which would have necessarily produced anomalies such as our existence.
Circling back to the original discussion on the thread, depending on which logical option we choose, it directly impacts the way we calculate the likelihood of life in other planets in the universe. Option 1 increases the likelihood whilst option 2 decreases. Random mutations occur under both options which distinguishes both options from the standard arguments of the IDists.
See what I wrote above.
Also, the 'eyespot', the final adaptation I was referring to, is an organelle and hence the mere presence of randomly configured 'photoreceptor proteins in a single-cell organism' does not qualify as such a final adaption. Whereas the eyespot of the blue-green algae has existed roughly in the same form for at least two billion years, and hence qualifying as 'a final adaptation' (to be differentiated from all notions of 'eternal existence') for our purposes of evolutionary analysis.
In any case, if we assume that the earliest iterations of mutations preceding the evolution of the eyespot were light-sensitive spots without some kind of a nervous system able to use it to the organism's advantage, then we acknowledge these initial iterations had no sight advantage. Due to this problem, we can do what Hans Mohr does, and accept under basic knowledge of molecular biology that without a nervous system such a spot would not be advantegous and therefore we must assume a parallel mutation of a nervous system. If so, then we're only feeding into the argument of improbability (to be differentiated from impossibility).