The argument from “natural law” made sense in a pre-scientific church, but now that biology is a science, you can be pretty sure any theologian who uses the term “natural law” is only turning to biology if it confirms their theological biases. Catholic priests who use the term “natural law” to condemn homosexuality are being dishonest almost by definition. If the laws of nature were really their guide, they would know that homosexual behavior is not unknown in the wilds. What is more unnatural or uncommon in nature among species that use sex to reproduce, is their own practice of voluntary celibacy.