This Stack Exchange thread has some fascinating answers and links to sources: https://biology.stackexchange.com/questions/2874/why-are-there-exactly-four-nucleo

This Stack Exchange thread has some fascinating answers and links to sources: https://biology.stackexchange.com/questions/2874/why-are-there-exactly-four-nucleobases-in-dna https://biology.stackexchange.com/questions/2874/why-are-the...