Hi Kahlan,
I see your point, but there is actually a difference between the three methods.
To put the different methods in order from more to less "screening" (which you could loosely associate with natural selection), they are:
In terms of "delivering sperm" via a syringe into the vagina, well there is no real difference between this and intercourse in terms of natural selection.
IUI only really gives the sperm the advantage of getting into the uterus. They still need to make it into the fallopian tubes to get to the egg, enter the egg, etc.
IVF offers a less hostile environment for the sperm then IUI, but the sperm still need to have the motility to get to the egg and be able to enter the egg, etc.
ICSI is completely different as the sperm is selected by a lab technician. The sperm need have no motility at all as it is transported to the egg by the technician. Finally, the sperm needs not have any ability to enter the egg as it is injected directly into the egg. ICSI is the equivalent of the forcing together of the selected sperm and the egg.
The physical characteristics of a sperm is only one part of creating a child. A good example is DNA mutations in an older male. The sperm all look fine, but most are what could be called "bad".
The process is from a sperm and an egg to an adult. Natural selection does no stop upon fertilisation. Natural selection is the reason why 5 in 6 pregnancies end in early miscarriage. If the combination of chromosomes from the sperm and the egg are not right, then the embryo does not continue developing. Only the best embryos continue development. Close enough is not good enough in nature and this is what natural selection is all about.
Studies have found that most couples do not want to donate their embryos. Most couples also do not wish their embryos to "perish". Thus the numbers of embryos in storage is growing quickly.




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