If eye components were added on by evolution why the removal of components(eg. by gene knockout) results in blindness?

Question

If eye components of some organism were evolved through a gradual series of tiny steps, by adding components one step at a time, then removal of components would not result in blindness but in some simpler visual system. If we start from the assumption that visual system is the evolutionary superstructure, which means that system is an upward extension of a previously existing and functional visual system, then logical necessity of component removal(eg. by gene knockout) from this superstructure is retention of visual function. But, experiments and countless medical examples showed that that is not the case.

How do you explain this contradiction between theory and observation?

Answer 1

If evolution proceeds by a series of small steps then it should be able to retrace that path by reversing each step in sequence. Just saying "The eye BUILDS and MODIFYs on each step" doesn't work because each modification could be separately reversed.



However gene knockout is unlikely to precisely retrace all the separate steps so it is not surprising that it is catastrophic.

Answer 2

Part of the answer lies in that not all gene expression is equal. Sight is the result of a number of different genes working together. These genes all evolved together over millions of years and some of those genes have more of an effect than others. Some genes turn on and off other genes



As already mentioned, evolution isn't always addition of components, sometimes it's change in function of something already there. Changing genes isn't a simple as adding one piece at a time like a Lego set.



In any case, blindness by knocking out a gene is usually by disabling one of the genes that has an effect on other genes. Failure of one of the HOX genes can leave the organism without any eyes at all, even though it's only one gene out of hundreds that affect sight. Failure of a less critical gene may result in color blindness, but otherwise not affect visual acuity at all.

Answer 3

You start with a false assumption - "Adding components"..



Evolution is mostly by slight, gradual changes - the members of a species have slight variations, as. eg people are all different heights, hair colours, eye colours, body proportions.



If one of those variations becomes a survival advantage, the over time more of the species will have that variation and less without it.



Sudden "additions" can happen via mutations or recessive genes - like the occasional person that has six fingers - but are extremely rare compared to slow progressive adaptations.





eg. the eye likely started as sensitive cells on the surface, then cells in a slight recess, gradually becoming a pit (and getting more directional), then the pit being liquid filled by trapping sweat or skin oils and so on.



If the lens on someones eye is damaged, the no longer see proper images but they can still tell which direction a light source is - that's about the same as the cells-in-a-pit primitive eye.

Answer 4

The eye BUILDS and MODIFYs on each step. The modification prevents backward compatibility. My 1st computer had 640Kb of RAM, the most Bill Gates said we would ever need. My current computer has 64Gb of RAM. My software is not backward compatible to 640Kb. My computer and software has evolved to the larger RAM. Take away RAM from my current computer and my software will not work. For example: My 1977 version of Lotus ran fine on 640Kb, but my 2012 MS Excel needs several Gb to work. Lotus and Excel are both Spreadsheet programs. Excel does the same thing Lotus did, AND MORE, better, faster. I could NOT run Excel on my 1977 machine. Spreadsheets have evolved to take advantage of the huge increase in available RAM.



2nd Example: At the Cuban Revolution, circa 1958, the Cubans had a large number of US made automobiles. With the Cuban Embargo, the Cubans could no longer get spare parts for their Chevrolets (of example), so, they made their own parts and kept them running. One common modification was, when needed, they replaced SAE nuts & bolts with Metric nuts and bolts. They did this by boring out the SAE bolt holes to the next size metric and tapping the hole to the next metric size. Result: A 1958 Cuban Chevrolet cannot use spare parts from a 1958 USA Chevrolet. The parts no longer fit and are not backward compatible.

Answer 5

You've made this stupid "argument" dozens of times now, and had it explained to you dozens more. I'm starting to have just the tiniest bit of suspicion that perhaps you're not asking out of pure intellectual curiosity.