He did engineer the process for diversity. It's not the same process that created life in the first place. We know how evolution works and there's not one passage that hints that it could produce any life on it's own. In fact, the scriptures go into good detail to rule out any idea other than God laid the entire foundation in 6 days.
The theory of evolution describes the mechanisms and processes of how life evolves, hence the term evolution. The origins of life is a related, but distinctly different set of questions; and even a naturalistic cause can be identified this does not by any stretch rule out the activity of God anymore than the activity of God is present in other firmly established natural phenomenon--the tides, sexual reproduction, the orbits of celestial bodies, gravitational forces, et al.
A naturalistic explanation for natural phenomenon does not rule out the presence or activity of God; if one ever were to suggest this (I'm not claiming you explicitly did this here) it becomes theologically problematic at best and produces a "God of the gaps" which is, fundamentally, incompatible with Christian theology which posits God as fully present and active in His creation.
Naturalistic explanations do not rule out the activity of God, whether we're talking about, again, the origins of life, evolution, or gravitational forces.
As far as how we ought to read Genesis 1, we might be wise to listen to what our forefathers in the faith have said:
"
It not infrequently happens that something about the earth, about the sky, about other elements of this world, about the motion and rotation or even the magnitude and distances of the stars, about definite eclipses of the sun and moon, about the passage of years and seasons, about the nature of animals, of fruits, of stones, and of other such things, may be known with the greatest certainty by reasoning or by experience, even by one who is not a Christian. It is too disgraceful and ruinous, though, and greatly to be avoided, that he [the non-Christian] should hear a Christian speaking so idiotically on these matters, and as if in accord with Christian writings, that he might say that he could scarcely keep from laughing when he saw how totally in error they are. In view of this and in keeping it in mind constantly while dealing with the book of Genesis, I have, insofar as I was able, explained in detail and set forth for consideration the meanings of obscure passages, taking care not to affirm rashly some one meaning to the prejudice of another and perhaps better explanation." - St. Augustine of Hippo, On the Literal Interpretation of Genesis
Now Augustine adhered to an allegorical interpretation, that God created the universe instantaneously, in a single moment, based upon his reading of Sirach 18:1; and read the six days as a wholly allegorical affair.
I don't read Genesis 1 allegorically, but Augustine's wisdom here is as relevant today as it was 1600 years ago. I adhere to the
Framework Hypothesis, which is significantly different from either an allegorical or historical-literal interpretation. It's what I think makes the most sense of the text without doing harm to the text, a purely historical-literal reading of Genesis 1 is, I believe ultimately too difficult to maintain given what the text actually says (e.g. in the beginning when God starts creating heaven and earth, there is already a primordial ocean). Additionally, Genesis 2 offers a different list of events entirely: Genesis 2 says clearly that no vegetation existed on the earth before God created Adam, it is only after Adam that God plants a garden (Eden), and after this God forms from the ground beasts and birds and living things.
Genesis 1 - Man -> Vegetation -> Animals
Genesis 2 - Vegetation -> Animals -> Man
If the intended purpose of Genesis 1 was to outline the historic and literal mechanisms and history of how the universe and world came into existence such a reading causes far more problems then it could ever hope to solve; both textually, theologically as well as ultimately scientifically.
I grew up a Young Earth Creationist, I just ultimately could not continue being one if I wanted to take the Bible and my Christian faith seriously.
-CryptoLutheran