Imagine pressing pause on a pregnancy until the timing is just right.

Many mammals, including bears, seals, otters, weasels, and kangaroos, can do something remarkably similar through a process called embryonic diapause. After fertilization, the embryo develops into a tiny ball of cells and then temporarily stops growing instead of immediately implanting in the uterus.

The embryo can remain in this suspended state for weeks or even months. When conditions improve, such as food becoming more abundant, the weather becoming more favorable, or the mother finishing raising her previous young, hormones signal the embryo to resume developing.

By delaying pregnancy until the timing is right, these animals give their offspring a much better chance of surviving.