At first, people used the same positions they would have taken for a painted portrait: something neutral. There were no smiles, that's for sure. But as photography became more popular, so did smiling in photos. The data also shows that women "significantly and consistently smile more than men.” You can see how the smile slowly grows from decade to decade in the image above.The researchers also pinpoint hairstyle trends — such as '30s finger waves, the bouffants and afros of the '70s, and the long, straight hair of the 2000s. We wonder what other interesting findings will come out of studying this massive trove of photos; maybe the researchers can explain why some heartthrobs were always dreamy, and others once looked like this