One of the more irritating tactics of evolutionary apologists is their habit of hand-waving.
An example of this is when people express doubts about the ability of random mutations to produce the features we see in organisms.
"Not to worry," says the evolutionist. "Whilst mutation is random, natural selection is not. Natural selection does the hard work needed to ensure that only those mutations that lead to the favourable outcome are preserved."
Even if we leave aside the fact that educated evolutionists dispute whether mutation and natural selection are able to achieve this end (for example the book "What Darwin Got Wrong") natural selection is not deterministic. Natural selection only favors survival, but the requirements of survival varies with the environment.
To give an analogy, one person rolls a 20 sided dice (D20). This is the survival criteria. He then rolls another D20, this is the rate of environmental change. A second person then rolls another D20. They have a number of tries equal to the second roll to attempt to achieve the first. If they fail to do so then they are eliminated.
Like this analogy the requirements and environmental changes of natural selection are fairly random. Consequently it cannot offer the kind of determination that evolutionary advocates demand.