Take the Chicxulub asteroid strike that impacted what is now the Yucatan Peninsula in Mexico approximately 66 million years ago. There is significant evidence that suggests that this asteroid strike, which left a 110-mile wide crater now buried nearly a mile underground, triggered the mass extinction at the Cretaceous-Paleogene boundary that killed off the dinosaurs. This mass extinction emptied ecological niches throughout the planet that could now be filled with novel plant and animal life.
In my view, evolution was the most efficient and fruitful way for God to use non-personal instrumental causes to create novel life forms after this planetary-wide extinction event, because a Darwinian evolutionary mechanism can shape and transform pre-existing life forms so that their surviving progeny can diversify and adapt to the increased number of available ecological niches. Once he had chosen to use non-personal instrumental causality to better manifest his glory, how else could God have used the non-personal instrumental causality of matter to create the novel kinds of mammals and birds that emerged to become the dominant land and marine vertebrates after the Chicxulub asteroid strike wiped out the dinosaurs?
Next, because of the fittingness of evolutionary creation, I also maintain that God did not “waste” life when he chose to create via an evolutionary process. This is a charge often levied against theistic evolution by creationists. For example, Henry Morris of the Institute for Creation Research argues in Exploring the Evidence for Creation that evolution cannot be reconciled with Christianity because, “the standard concept of evolution involves the development of innumerable misfits and extinctions, useless and even harmful organisms. If this is God’s ‘method of creation,’ it is strange that He would use such cruel, haphazard, inefficient, wasteful processes.”
In response, no one thinks that Michelangelo “wasted” marble because there were leftover marble pieces after he had completed sculpting his masterpiece, David. There is no waste when the agent fittingly attains his end. Likewise, I propose that extinct species are not pointless waste. Rather, they were the necessary “leftovers” from the creative evolutionary process that God used to generate the novel and diverse forms of life visible today in a manner most fitting to reveal his glory.
Finally, according to St. Thomas, God created the diversity of creatures because no single creature can adequately reflect the perfection of God:
We must say that the distinction and multitude of things come from the intention of the first agent, who is God. For He brought things into being in order that His goodness might be communicated to creatures, and be represented by them; and because His goodness could not be adequately represented by one creature alone, He produced many and diverse creatures, that what was wanting to one in the representation of the divine goodness might be supplied by another. For goodness, which in God is simple and uniform, in creatures is manifold and divided and hence the whole universe together participates in the divine goodness more perfectly, and represents it better than any single creature whatever. (Summa theologiae, I.47.1)
Therefore, in my view, it was also fitting that God created via evolution rather than via special creation because in doing so he was able to create more species to reflect his glory: With evolution, he created four billion species over a three billion year period, which is significantly greater than the mere eight million extant species today. In fact, it would have been ecologically impossible for all four billion species to co-exist on our planet, because there are only a limited number of ecological niches on the planet at a given moment in time.
To put it another way, there is a limit to the number of species and individual organisms that can be sustained by the planet at any one moment in time. Some of them are even mutually exclusive: If they had been created together, the large carnivorous dinosaur, Tyrannosaurus rex, would likely have wiped out the Asian elephant, Elephas maximus. However, with evolutionary creation – and not with special creation – these species were able to exist at separate moments in history to uniquely manifest the glory of their Creator. Again, they were not wasted.
To sum up, why did God choose to create via an evolutionary process rather than via special creation? Because it better reveals his glory and his power. Because it reveals better that he is God.