If evolution and abiogenesis have simple naturalistic explanations, then why can we not simply exclude God from creation of life and species?
If evolution and abiogenesis have simply naturalistic explanations behind the origins and development of life itself, then wouldn’t this replace any need for a god? Abiogenesis for example gives forth purely scientific and naturalistic reasons behind how life came into existence, why at this point would there be a need for such a deity? Same with evolution which gives reason behind the emergence of species, surely there is a strict naturalistic reason behind the appearance of all life forms that exclude God. Is there any method in which God can be integrated into these processes?
The answer to your question must come from a couple different directions because you actually raise a number of issues here. Please forgive me if I approach this question from more than one angle.
First of all, your question seems to presuppose that a successful theory of evolution and a successful theory of abiogenesis exist. In the case of evolution, it is fair to say that there is a quite successful theory to explain the origin of the diversity of species. I will speak below to the unwarranted assumption that the path of evolution is fully without supernatural intervention, but let me just say that the theory of evolution by natural selection, with the source of variety coming from mutations of DNA is a good theory by almost any definition. It has broad predictive powers, it is in general (though perhaps somewhat debatable) agreement with the fossil evidence and is in excellent agreement with the DNA evidence. The idea of common descent is virtually a slam dunk, scientifically.
Having said that, there is NO viable scientific theory of abiogenesis. Let me put this fairly simply. In order for life to spontaneously appear from prebiotic non-living matter three steps would absolutely have to occur. First, the simple building blocks, known as monomers, such as amino acides, monosaccharides, lipids and nucleic acids would have to be synthesized from simpler building block molecules by random, natural processes. Second, these monomers would have to self-assemble into much larger polymers, which are chains of the small building blocks. These polymers are polypeptides, polysaccharides, more complex lipids and nucleic acids. The third step in abiogenesis is the creation of usable information within these polymers through a sort of prebiotic survival of the fittest, to create the fantastically complex system which could have the functions of incorporating energy, building new molecules, divide to create more life and so forth.
Of these three steps, there are believable mechanisms for the first step. Arguably, scientists have shown that amino acids, monosaccharides, lipids and nucleotides can self-assemble. The problem with this is that the environment necessary for amino acids to be produced spontaneously does not produce monosaccharides, lipids or nucleotides and the environment which allows the formation of nucleotides, similarly, does not allow for the formation of the other three. This is a huge barrier to forming a believable theory of abiogenesis, but perhaps it could be overcome.
The second step is more problematic. As far as I know, there has not yet been created any artificial environment in which nucleic acids form spontaneously. An environment with limited activity to create polypeptides has been shown experimentally.
It is the third “step” which is the real problem. There is not even a conceivable mechanism, never mind a real one, in which the fantastic amount of information required to produce an actual living thing can be created naturally. Attempts to do so have all failed spectacularly. There is no mechanism in nature by which information can be built up unless there is information put into the system in the first place. Species can evolve and new information can be created in such information-rich systems, but, bottom line, information is not and as far as scientists know, cannot be created naturally.
So, your presupposition that there is a successful theory of abiogenesis is completely false. For this reason the rest of the question is a bit academic. It would be a bit like asking if we could go to another galaxy tomorrow what would we observe? This is an interesting question but it is also a nonsense question because we cannot go to another galaxy tomorrow. It would be a bit like asking what we would observe if we had been around before the big bang happened. A great question, but one which is entirely speculative, with no basis in reality.
Now, let me get to your main question. What if we had completely believable mechanism proposed which could explain both the origin of life and the origin of all observable species? Would this mean that we no longer need God to explain anything at all? Would this not mean that we could simply discard the notion of God entirely? The answer to this question is absolutely no, for several reasons. Remember that the very question itself is based on a false premise, but let us run with the question anyway, as it is still an interesting question. By the way, Isaac Newton and other deists did reach a similar conclusion and they did speculate somewhat on this question. Some atheists have done so as well.
Let me propose a few reasons that even in this extremely unrealistic scenario, God still could and, indeed would have to fit into things. First of all, the scenario assumes a-priori that the universe itself exists, with the laws of nature in place. This brings up a very difficult question. How is it that anything at all exists? Why is there a universe? This is a fundamental question which science has not and cannot answer. The multiverse theory which is a highly speculative and virtually non-scientific theory, is really just a work-around to this questions. Why does the universe have the laws it has? Why is it that the laws of the universe we live in are so fantastically well-tuned so that life can exist? Here is the cold, hard fact. Science provides no answers to these questions. The bottom line is that the universe appears to have come from supernatural origins.
Besides, even if there were a viable natural mechanism which could be invoked, in principle, to explain the origin of species, this does not preclude the existence of a Creator or of a supernatural being. There is literally no way to prove that this supernatural power which created the universe in the first place did not also intervene in the evolutionary process. Personally, I believe that God HAS intervened. I believe that there is no set of purely random processes which would have produces human beings, with our self-awareness, with our billions of base pairs of information, with consciousness, with a sense of morality, etc. I cannot scientifically prove supernatural intervention, and neither can non-believers prove that there was no supernatural intervention. At best we are at a stale mate here, and I am very strongly convinced, from looking at the evidence, that God has directed change from simple life to the vastly complex beings which exist.
You say, “surely there is a strict naturalistic reason behind the appearance of all life forms that exclude God.” My response is that this is simply an assumption, that it is an unprovable assumption, and that, from my take on the evidence it is in fact an assumption which is rather unlikely to even be true, never mind something we can simply assume and work from there. Now, it is true that philosophically-committed materialists use this as a working assumption, but if we use naturalism as a philosophical basis to “prove” that there is a strict naturalistic explanation to the origin of species, this would be circular reasoning and therefore would be a completely invalid argument.
To summarize, yes, there is a way to integrate the idea of God into what we know about the origin of life and of species. In fact, I have concluded from basic scientific laws that there is literally no way to explain the origin of life without invoking some sort of supernatural intervention and the supernatural cannot be ruled out of the process of speciation as well. Bottom line, science needs God and no amount of yelling and screaming by atheistic committed naturalists will change this.