At which site on the ribosome does the transfer rna dock initially during elongation?

Which macromolecule catalyzes chemical reactions this be considered enzyme chemical reactions thus he considering enzymes

Asquirrel population lives in an area. over many years, a river in that area grows wider and stronger, eventually forming a canyon. the squirrel populations on the two sides of the canyon can no longer mate with each other and ultimately form distinct species. this is an example of

Ascientific idea becomes valid when it is what?