If you thought sideburns were really making a comeback in the first half of the 2000s, it might not have been your imagination. Over at the Data Is Beautiful subreddit, one extremely dedicated user has visualized 100 years of university hairstyles by going through yearbooks and categorizing them by hand. That means cataloguing over 90,000 yearbook photos.

Take a look.

Believe me, this was no small feat. User Mystic River went through 100 years of yearbooks at four Canadian universities, counted the facial hair styles individually, and put them in an Excel sheet. Since this was done by hand, Mystic River acknowledges that the methodology has room for error, since “it's a bit of a judgement call between what is a sideburn and what is a muttonchop.” Also, there was the need to leave out some photos in the 1970s of men who had “very long hair that completely obscured their cheeks.”

To be fair, even though this encompasses so many images, it is geographically limited. Still, some of the trends are pretty striking. What happened in the late 1970s and early 1980s that led to men shunning the clean-shaven look? Why don’t we see the full beard before then? And why the interest in goatees (one of the worst forms of facial hair, thank you very much) in the early 2000s?