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

Question

If reproductive system 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 infertility but in some simplest mode of reproduction. If we start from the assumption that reproductive system is a evolutionary superstructure, which means that system is an upward extension of a previously existing and functional reproductive system, then logical necessity of component removal(eg. by gene knockout) from this superstructure is retention of reproductive function. But, experiments and countless medical examples showed that that is not the case.

How do you explain this contradiction?

Answer 1

Evolution is not a simple as you think. It does not progress by simple add-ons. Much of evolutionary change is due to modifications of developmental genes which affect the organism at an early stage of its ontogeny.These changes have an effect on much more than just one target organ. In other words, genes act in a complex interactive manner.

Answer 2

There is no contradiction. An analogy of an evolving system is the automobile. Changes have been made to its various components throughout the many decades since its invention. If you take out one of the components, for example, the starter, the alternator, the engine, the tires, or the steering wheel, then it is not going to run. However, there are components that can be removed and the car still runs. For example, if one removes the rear seats, the top of the car (making it a convertible), or the trunk (making it a hatchback), the car is still functional.



Similarly, if you remove parts like the clitoris (a practice known as genital mutilation that is still practiced in some African countries) or if you circumcise a male, they can still reproduce. OTOH, if a vasectomy is performed or if the male testicles are removed, there will be infertility. So, if the genes that code for the clitoris or the foreskin are disabled, there is no impact on fertility. You cannot argue that the foreskin or clitoris are not the product of evolution, since they were not present in the beginning when sexual reproduction first evolved. In fact, the penis did not evolve until after amphibians have evolved into reptiles, but sexual reproduction evolved long before amphibians evolved. Just like the car, there are some components of the reproductive system that cannot be disabled and some that can be without causing system failure.

Answer 3

Evolution does not work by gradually adding bits to a pre-existing structure, while at the same time retaining the pre-existing structure. In other words, evolution is not like building something in Lego.



Let's say we have an organism that has a reproductive system made of components A, B, C and D. Over time another component, E, which starts off with some function which is unrelated to reproduction, becomes modified to become part of the reproductive system. So then we have a new species whose reproductive system is made of components A, B, C, D and E.

What you are asking is "If we remove E, why doesn't the organism still have a functioning reproductive system made of A, B, C and D?". Because A, B, C and D have not stayed the same as they were in the ancestor species. They have *also" changed their structure such that their correct functioning is now dependent on the presence of component E.