The kids are getting... dumber.

I teach high school history and I've been teaching for 15 years. Over the past 5 or 6 years, I've really started to notice a decline in overall intelligence and cognitive function of the students I'm encountering. They just seem... dumber. They're not as capable of critical thinking, they have a hard time answering anything but the most basic questions, and they don't seem to retain any information sent their way. I've always had to deal with the occasional "dumb kid." Now it seems like half the class can't figure out how to use the glue stick. I'm beginning to wonder if some sort of decline in human intelligence is possible because of how out of control social media is and how everyone is glued to their phone 24/7. I know it's probably just my old ass grumbling, but am I the only one who is concerned about the future of humanity?