There’s a beginning for all living things, for good or ill. No creature simply appears; it must evolve gradually, from a single cell into something far more complex. Or, it must be created.
In some cases, its genesis might be a combination of both.
The Doctor was sent to Skaro on a mission; avert the creation of the Daleks, or ensure that they evolved as less aggressive and xenophobic creatures.
He failed in both respects; perhaps their creation was a fixed point, but he had to believe that despite their destructive tendencies, some good might come out of their existence.