Orthogenesis

Orthogenesis is a theory that says that some species change over time in the same direction, like they have a goal or direction they're moving in. It's kind of like they find directions, or they are guided, like they have a map, and they know where they are going. For example, if a species of bird gets bigger, then all the birds of that species will get bigger in the same direction, even if there's no reason for them to do it.