So natural law is a system of beliefs that by observing nature, you can derive universal truths from nature and then apply those universal truths to human behavior and what is good and what is bad. Natural law while being something that in reality has no required connection to Christianity does share a deep historical connection to Christianity for the Catholic Church has and still does use natural law to help shape theological pronunciations.

So what does it say about natural law, when you have something like this in nature, something that on its face is so abhorrant. From wikipedia (chosen for its simplicity)

The Bruce effect, or pregnancy block,[1][2] refers to the tendency for female rodents to terminate their pregnancies following exposure to the scent of an unfamiliar male.[3] The Bruce Effect was first noted in 1959 by Hilda M. Bruce.[4] The effect has primarily been studied in laboratory mice (Mus musculus),[1] but is also observed in deer-mice,[5] meadow voles,[6] and collared lemmings.[7] In mice, pregnancy can only be terminated prior to embryo implantation, but other species will interrupt even a late-term pregnancy.[ The Bruce Effect has also been observed in geladas[9] and it has also been proposed, but not confirmed, in other non-rodent species such as the lion.[10]

So in nature male 1 gets female pregnant, but male 2 produces pheromones that causes female to either not implant the embryo or in some species to abort the fetus that was already implanted.

Abortions happen in nature, what does this say about natural law? Is it so universal? And before you bring up the fall of man, what does man's sin have to do with mice?