Sperm penetration tests check to see whether a man's sperm can move through cervical mucus and the fallopian tubes to join with (fertilize) an egg. This test is usually done when a couple is having trouble becoming pregnant (infertility). There are different sperm penetration tests.
The idea that a boundary is shifting can be applied to different areas. A shifting frontier of science would be referring to the fact that science is always changing and growing, and always with new areas. In wartime, a shifting frontier would be an international border which is constantly being renegotiated.
Alaska: The Last Frontier. Alaska: The Last Frontier is an American reality cable television series on the Discovery Channel, currently in its 6th season of broadcast. The show documents the extended Kilcher family, descendants of a Swiss immigrant Alaska pioneer, at their homestead 11 miles outside of Homer. By living without plumbing or modern heating, the clan must subsist by hunting and preparing for the long winters. The Kilcher family are relatives of the singer Jewel.