"The simplest organism capable of independent life, the prokargote bacterial cell, is a masterpiece of miniaturized complexity which makes a spaceship seem rather low-tech."
Johnson, Phillip. Darwin on Trial, Washington, D.C.: Regnery Gateway, 1991.
"When the existing theory of evolution is seen as inadequate do we abandon it or broaden its base?"
Sharka Todd, 2014
The problem of how life forms came into being in the physical universe is a big one that has never been adequately answered by science. It is one of a number of "miracles" that materialistic science cannot explain. Many are under the mistaken belief that science has answered all these questions or is part way to doing so. Nothing could be further from the truth. The more we understand life, the more we realize how complex it is, and how it needs intelligence to create and organise it. In other words, there needs to be an interior life (consciousness) with great intelligence and the ability to create sensory apparatus so that the organism can exist in an ongoing fashion in this physical dimension.
The walk-in theory
Many people think the only alternative to the scientific materialist view of the origin of life is the belief in a creator God such as the one Christians, Muslims and Jews believe in. While the belief that everything that exists originally came from the one super being is common (but with no explanation for how that being came to be), there is another theory to explain physically-based life. This theory is called the walk-in theory. It doesn't do away with the problem of how life originated but it does explain how it came into this physical dimension. It walked in, or materialised, from another reality. This alternate reality is generally believed to be a more "mental" reality than the physical world. In fact, you could say that life "dreamed itself" into this reality. This is the view of a number of philosophers but it isn't a view that can be readily proven scientifically, hence scientists have no interest in it. However, just because a thing cannot be proven scientifically doesn't mean it doesn't exist. In fact, because of the limits and demands of physical existence you could argue it requires such a level of complexity from life forms to exist here, even in the most basic of forms (see the quote at the top of this article), that they couldn't have evolved from scratch in this reality! Instead, it may be required that intelligences first exist in an environment (reality) that is far less demanding and then evolve to a level of ability that enables it to manifest in this highly demanding physical reality.
Why propose multiple realities?
Many will argue evoking alternative realities unnecessarily complicates theories of evolution and that it is better to stick to just one reality- this physical reality. But if we come up against a wall which makes the origin of physical life from inert matter seem impossible then we have to broaden our analysis to include other possibilities and even other realities. This is similar to what physicists are doing to explain how this universe happens to be optimally primed for life. They are evoking the notion of parallel universes to help explain this strange set of affairs- the likelihood that a universe should emerge from nothing having physical laws that support the evolution of life within it, without an intelligence there to guide it. To explain the incredible unlikelihood of this occurring they imagine the existence of trillions of "parallel" universes existing in their own time-space continuum, where one or more of these, through chance, has the physical laws operating within it which enable life to evolve.
But this doesn't explain the origin of life
This "multiple realities" theory of evolution doesn't explain how the first intelligence came about which then evolved into a state where physical existence become possible. What is does say is that intelligent life (there is no other) could not have evolved from inert matter in this universe. As a result, it envisions another reality where an intelligence can evolve into a form intelligent, complex, and creative enough to be able to create a sufficiently complex life form able to exist in this (physical) reality. This doesn't do away with the problem of how the first intelligence came about. It just states that it couldn't have happened in this physical universe due to the constrains of this world. In fact, I would suggest the human intellect is incapable of understanding how or why the first being/consciousness/intelligence came to be. The fact that something exists rather than nothing is something that I have never seen an adequate answer to.