By "nonsense," I don't mean that this explanation of evolution isn't true. Because it is.
The thought experiment described in the video came from Richard Dawkins, someone who knows what he is talking about when it comes to the origins of life on Earth. Here he describes the thought experiment in words.
The nonsense reference flows out of the difficulty I have understanding how there can be completely different species along an evolutionary branch of the tree of life, but at no time was there one individual who was this species followed by a relative who was an individual of another species.
Yet here we are today, Homo sapiens, a specific species.
It seems clear to me that the problem lies in how the human brain works -- mine, yours, everybody's -- rather than in how reality is.
We're prone to making firm distinctions.
Hot/cold. Man/woman. Atheist/believer. Liberal/conservative. Dead/alive. Conscious/unconscious. And so on.
Dawkin's thought experiment challenges this way of thinking. He says that every single creature you are related to in a 185 million generation ancestry was the same species as its parent. Yet way back you were related to a fish, and now you are a human.
Go figure. (It's tough.)
Evolution is incredibly slow. Also, gradual. Dawkins says it is like you growing from a baby to a toddler. At no time were you a baby at one moment and a toddler at the next. Yet you became a toddler after being a baby.
Likewise, in his talk Dawkins says you can't see the hour hand of a (traditional) clock moving. But wait an hour, and you'll see that it has moved quite a bit.
There's something really important here about how we understand and misunderstand reality. I just wish I better understood what it is.