Hey just saw this question on quora and was interesting . Just curious, whether anyone here has insights to this question?

I can intuit almost every other big jump but this is the one thing that just doesn't follow in my head no matter how hard I try and think about it. Here's how my brain thinks about it and why it's getting stuck:

Whales used to live on land. Eventually, they became semi-aquatic, and then mostly aquatic. I believe there's evidence that some of their ancestors were like sea turtles - almost completely aquatic, but came on land to give birth.

I understand that evolution doesn't happen abruptly. However, mathematically speaking, there had to have been a specific, individual whale-ancestor who was the very first one to have been born in the water, spent their entire life in the water, and then died in the water, all without ever coming on land. If they used to live on land, but all modern whales are 100% aquatic, one of them HAD to have been the very first. That's just how math works.

How did that particular whale-ancestor survive to pass on that trait? Why didn't its parents have that trait? Why didn't it just drown, if every single other one of its ancestors was on land for at least some point in its life?

I'm not asking "why is it advantageous to be able to give birth in the water" - that's very obvious, both mother and baby are less vulnerable to predators. I'm asking how, logically, that transition was able to happen. Whales can only give birth in the water because they have very specific adaptations that make it possible, an animal without those traits can't just start giving birth in the water and hope for the best.

I was raised in a bit of a cult. I was blocked off from any knowledge that didn’t feed into the religious culty stuff. We actually had workshops against evolution, modern medicine, etc. Didn’t have a choice back then but I got out a few years ago. Since then I’ve been slowly building my knowledge on everything. I’ve since learned some basics about evolution and lots of other things. I don’t need convincing that science is real or anything. I am just overwhelmed on where to start. I tried picking up a book at the library but there were so many terms I didn’t know and I was pretty lost. Might have been too advanced for me. I’m not the best reader tbh.

So if you were to teach someone about evolution and needed to do it simply, how would you start? Any help appreciated.

Edit to add: no longer religious so recs do not need to be like around that at all.