In Richard Dawkins' (excellent) 1986 book The Blind Watchmaker, he uses the analogy of a nine dimensional 'biomorph space' (he could have used any number of dimensions, he said it was nine for relative simplicity, and I may be using the wrong phrase with 'biomorph space' but I'm pretty sure he used that one) to describe evolving creatures, that an error in coding of DNA would move the creature one place in the biomorph space, so a dog would be in one position of the space, and a human would be in another, and by having errors in DNA as they reproduce, steps could be made towards/away from each other (I could have explained that hopelessly badly but hopefully you get my gist!). What I was looking for was an arbitrary multiple to describe how far away different features of a living creature are, that is if a creature moved the shortest possible distance towards a feature, how long would it take relative to other features? As an example, say that developing legs takes x years, so eyes takes 10x (made those ratios up). What would the multiples be for, say, bat's sonar tracking, human ears, insect's poison glands? Assuming each feature was being evolved from the most basic organism, all multiples just relative to each other, exact/rough actual times don't matter at all. Obviously how effective the organ is plays a vital role in the shortest possible time it would take to evolve, so assume each organ would be described as competent for its function. Apologies if that was a bit of a scientific car crash of a message haha. The thought experiment he used is known as the 'Weasel program'.