Ask HN: How do jobs get created/expanded in fast growing companies?

I'm interested in learning how big tech companies like Facebook decide how and when to specialize development teams in order to scale up, from their journey from a few employees to many thousands and a massive market cap. Especially from the POV of an employee.

Having worked at only smaller companies (the largest I've worked at has 200 employees, only about 20 that are in IT and programming), and that do not have a numbering system for their employee ranks, it's a bit difficult for me to grasp how division of tasks is administered in the large tech companies.

For example, the very early Facebook and the one today are a world of difference. When they started, the tech side really was mostly coding PHP and the front end, and routine web host maintenance (from a third party service if they are really starting out). This is the kind of company I'm most familiar with. I am accustomed to building websites or apps for smaller clients that have small customer bases.

But today's Facebook is very different. They hire much more than web devs for their tech departments. I have no idea how they are organized internally, and trying to guess the hierarchy is way over my head. So seeing how a company evolves and grows will probably help me understand better. What are some good articles that give me an idea of how internal structures and division of responsibilities change within growing companies?