Physicist and atheist Fred Hoyle famously hated Fr. Lemaitre's explanation for the origin of the universe. In a radio interview, he derisively referred to Lemaitre's idea as the theory that a "big bang" started everything. The name was so catchy that it stuck, and Lemaitre's theory has, forever after, been known as the Big Bang theory.
Why did Hoyle hate it? Well, he was an atheist, and it sounded too much like Genesis: "Let there be light." As a complete sidenote, Hoyle would eventually become a theist (although not a Christian) because of his astrophysics. He developed a theory of how carbon atoms might be formed within the sun that later turned out to be correct. The fact that experiment proved him correct convinced him that God exists. He knew the only way his theoretical pathway could work is if Someone was monkeying with universal constants.
Now, I have no brief for creationism. I consider a six-day, 6000-year old Earth a silly theory given current evidence. Obviously, God created life, but, as Father and Doctor of the Church, St. Augustine, observed, the Bible isn't a science textbook.
However, this does not make me a fan of evolution either. Even worse, the math doesn't work well for spontaneous generation of life (which is actually a problem separate from that of evolution). Spontaneous generation is so mathematically unlikely, it is nearly impossible to believe. God clearly had to have had a hand in creating life, but exactly how He did it is a complete mystery to me. All I know is that some kind of life-generation event happened. That's why you are reading this and I am writing it.
Calculations vary widely for exactly how improbable that life-creation event was. Some people argue the event is very much more likely than we understand, and, given the number of stars in the universe, and the number of planets that must revolve around each star, it is therefore likely that life exists on many planets. But if they are right, that poses a problem for theories of evolution.
Here's the problem: if spontaneous generation is more likely than we generally calculate, then I can't see any particular reason life didn't spring forth from non-life many times on this planet, instead of just once. In fact, if life can come into existence from non-life multiple times during the life of the universe - which is the position of those who insist that other planets hold life as well as ours - then what possible difference does it make if life spontaneously generated multiple times on one planet versus one time each on dozens of other planets? Why do we insist it can happen only once per planet, each planet separated by many light years? There is no particular logical or mathematical reason to make a geographical distinction. The universe is calculated to be about 14 billion years old, the earth between 4 and 6 billion years old. Taking the age of the earth and universe into account doesn't add any real improbability to the problem.
Indeed, it is possible that life cannot come into existence apart from DNA/RNA. Now, I know there are other theoretical models, but we have no living examples of them, so other models are all theory. It is possible the other models are wrong, that is, it is possible that there really is only one way for the universe to spontaneously generate complex life (life more complicated than a prion, which is not even clearly alive). Further, it is possible that this life-generation event sequence requires a specific base DNA/RNA material sequence in order to occur.
If that is true - if life has to be DNA/RNA to work - then it would actually make sense to see multiple "spontaneous generation" life events on the same planet. After all, if the conditions clearly obtained for the first event, then all the pieces are already present for the second, third, fourth, ad infinitum events.
Which would mean that all those mutually exclusive evolutionary "life trees" that we see are actually illusory. The different creatures on the planet only look related, but they actually aren't. Each species, genus, group, whatever level you want to call the cut-off, is actually the result of an entirely separate spontaneous generation, sharing, at most, a common chemical precursor. This theory seems as least as probable an explanation as the idea that spontaneous generation only happened once and everything else evolved out of that one, spontaneously generated, living creature.
Or, to put it another way, I am proposing a DNA/RNA version of the anthropic principle. All living things appear to be descended from a common ancestor not because they are, but because there is no other way to have life exist.
In this scenario, each species/genus/whatever represents for biology what each separate universe represents in the multiverse proposal.
But this theory poses what I will call the Hoyle Problem. Just as Big Bang Theory looked far too much like Genesis for any atheistic physicist to accept, so the theory described above looks far too much like Genesis for any atheistic biologist to accept. It essentially allows you to assume an individual creation event for each genus.
So, there is a philosophical objection. However, from a purely atheistic viewpoint, I can't see any mathematical objections to the possibility of multiple spontaneous generations on the same planet.
The calculations on a life-creation event are all over the board. Since we have never successfully replicated it, we don't really know what the odds of spontaneous generation actually are, at least not in a concrete way. But, from the mathematical perspective of improbability, it is not like we're talking about different classes of large numbers. No matter how improbable the first event, once the first event occurs, the second can only be as improbable, and, if the second is to happen on the same planet under the same conditions, possibly quite a bit less improbable then the first.
If spontaneous generation processes can operate concurrently in different geographical locations (several different planets all having a life event), then there is no strong argument against having several of those concurrent processes happen in the same geographical locale as well. Which means that creationism, in this modified form, may well be correct.