Can Humans not spawn with the immortal trait anymore?

I wanted to create a group of humans who were all born with the Immortal trait. I created a world, created a few humans, turned off all laws that could cause them to die, let them build up until there were ten thousand of them, and then turned off births and waited till everyone died of old age. I had already done this a few times two years ago, and it worked perfectly, i got several naturally immortal people through that. This time there where none. i tried it several times but it never worked. Can humans not spawn with the immortal trait anymore? From what ive read it should be one in 1000 normally.