I mentioned seeing two blowholes on the humpback whales swimming near the house and did not know if all whales had two. Here is an explanation and answer from one of my friends: Baleen whales (like humpbacks, blue whales, gray whales, bowhead whales, etc.) have two blowholes, located side by side. Toothed whales (like sperm whales, beluga whales, dolphins, etc.) have one blowhole. Most mammals have two nostrils (blowhole equivalents). One of the nostrils (air-passages) of toothed whales evolved into their echolocation system (the sensing system in which they make and recieve high-pitched sounds in order to orient themselves, catch prey, and communicate), leaving them with only one blowhole.