I have heard of the sieve bit earlier. But that's nonsense too.
For one thing there is no specific size or shape being sieved. Everything from elephants, lizards, fish and spiders to crotons, apple trees, bacteria are being allowed through. What selection?
It is in fact wrong to talk of something being selected and something else not being selected. Dinosaurs were selected...not any more. Mammoths were selected....but not any more.
What is the time limit to decide whether something is selected or not? 1000 years, 10000 years, 1 million years, 100 million years. How long should it survive to be deemed selected.
It is more appropriate to talk of a big hole not a sieve, through which all species are passing through. Everything is selected for some time (however small) and everything is rejected after some time (however long).
Its more of a snap shot at one point of time. As at this moment, such and such species and organisms are selected. That's all it is. Maybe not by today evening. Some species could be extinct.
So...the concept of natural selection is 'trying to have it both ways'. You use a anthropomorphic concept of 'selection' as though it is some very clear and definitive process. Then suddenly it is not a selection at all.....just a reaction to random environmental changes!
People like to say....its not random at all...you don't understand....its Natural Selection! LOL!
Point is that Natural Selection is also random because environmental changes are random. So...random genetic variations ...'selected' through random environmental changes ....is very much random too.