Joel McHale has undoubtedly had a hair transplant. Apart from popular believe, he doesn't wear a hair piece nor did he get hair plugs. Rather, a few years ago he had a transplant to fill in the balding area around his temporal peaks as well as the on top of his scalp. If you remember in Spider Man (with Tobey Maguire), he had the balding head you see in the left picture. He had his first hair transplant just before the show Community started filming. Also, lately it looks like he may of had a second one to get even more density. In the end though, Joel McHale is looking great after conservatively done hair transplant.