The article has one very misleading mistake. Four [types] of apes have been able to see themselves in mirrors, not four apes as I watched a video of IIRC eight

The article has one very misleading mistake. Four [types] of apes have been able to see themselves in mirrors, not four apes as I watched a video of IIRC eight apes, four male and four female, who used mirrors for self grooming, playing with makeup and a number of other things along with a demonstration of the spot test. However, I think two were used to show that apes under a certain age couldn't recognise themselves, just like humans under a certain age can't. This was likely to show that apes have an intelligence higher than an 18 month old.