The room for radical revision regarding the inheritance of acquired characteristics is exceedingly small. The room for radical revision of Newtonian physics was even smaller. But it did happen.
It is far less frequent than the mutation rate.
Things tend to be "less frequent" when we do not look for them.
There is still no proposed mechanism [...]
That something is not proposed does not mean that it is not there. Actually I think that number of things we do not know and we do not imagine or propose is much larger. The world is a wonderful wast place.
Any directed variation would have to be able to see into the future to anticipate the next move the environment was going to take.
Why do you expect the directed variations to be obliged to see the future? Random mutations/selected models reacts slowly to the present changes. Directed variations would need to the same.
The only part of the sperm that is combined into the egg is the DNA.
I doubt that such research (excluding any interraction between spermoplasma and egg) was done. But even so, the DNA modifications or switches could be done before combination.
" The room for radical revision of Newtonian physics was even smaller. But it did happen."
It was a lot bigger with Newton. There is far less room for the inheritance of acquired characteristics.
"Things tend to be "less frequent" when we do not look for them."
Scientists DO look for the rates of ERV insertions; they are a lot less common then mutations.
"That something is not proposed does not mean that it is not there. Actually I think that number of things we do not know and we do not imagine or propose is much larger. The world is a wonderful wast place."
In order for something to be examined by science, there has to at least be the hint that it exists.
" Why do you expect the directed variations to be obliged to see the future?"
In order to be useful they would have to be. The designer would need to know what to design for. Otherwise, the changes would be indistinguishable from random mutation.
"Random mutations/selected models reacts slowly to the present changes."
Sometimes they don't react fast enough (extinction).
"I doubt that such research (excluding any interraction between spermoplasma and egg) was done."
It has been.
"But even so, the DNA modifications or switches could be done before combination."
By what?