Bloodline Enlightenment

Yale stopped using blood for the experiments with Shirk because Shirk's main problem at that moment was on another side.

The transformation into half-beasts happened due to the beast bloodline overtaking the human one, those who had it well integrated looked more like humans due to being able to avoid that overtaking.

In Shirk's case, the beast bloodline had the absolute advantage; Shirk was more lizard than human, everyone could tell it by his looks.

However, the bloodline alone couldn't transform a human enough to turn it like someone of the species of those invaders, people like Shirk are extremely similar, but in the end, they were still half-beasts.

The first step Yale needed to do was modifying Shirk's body to turn it even more similar to the invaders. Yale started by Shirk's skin; although it was already sturdy, compared with the details in the book, it wasn't enough.