What came first? The chicken or the egg? You've probably heard that one before, but eggs are truly everywhere (regardless of whether there’s a chicken around). Insect eggs are on almost every single plant, and fish and bird’s eggs can be found in every supermarket. Although humans are mammals, we also produce eggs. Without an egg, a sperm cell would be pretty useless after all. People who are born with ovaries are simultaneously born with all the eggs they’ll ever produce in their body. Weird but true.