Yeah, you can see tribalism even here on HN in discussions on different operating systems or programming languages. We are an animal that is irrational, predatory and highly social by nature. Whether we team up to build something useful or to fight with the other tribe depends mostly on the social programming done by the institutions of power such as media, schools and churches.
These institutions also have the power to decide what defines "our" vs "their" tribe. Just the usage of the terms "pro-life" or "pro-choice" already indicates that someone identifies with a specific tribe as the language is an important part of the collective identity.