Evolution, at the very most, could explain the movement from single celled lifeforms, to multi-cellular lifeforms, to lifeforms with a central nervous system, to human beings with conscious reasoning faculties and a sense of existential concern that transcends mere experience.
Although I do not believe that there are sufficient biological mechanisms for that sort of "molecules-to-man" evolution to take place, I do not mind granted the possibility for the sake of discussion.
So let's enter into the hypothetical world in which plants in the ocean evolved into fish in the ocean, fish in the ocean evolved into land animals, and land animals evolved into human beings (because that is what the modern theory of evolution describes).
Ok, now we have a hypothetical world in which we understand the development from "simple" lifeforms to human beings. However, the original question - about the origin of life itself - is still left completely unanswered. The vast majority of evolutionists actually prefer to ignore this question because they know that the question itself is both 1) a serious challenge to evolutionary theory, and 2) completely outside the realm of science.
The theory of evolution depends on the pre-existence of life. Evolution is an attempt to explain how "simple" creatures became human beings. It presupposes the existence of life, the pre-existence of a "simple" creature, and tries to explain how that original creature's descendants became human over time. So if you present an evolutionist with concerns about the origin of life, they will brush your concerns aside and tell you that the origin of life is completely irrelevant and erroneous when speaking of evolution. The validity of the theory of evolution, according to these people, does not depend upon the validity of an evolutionary mechanism for the origin of life, because (according to them) the evolutionary theory concerns the change that occurs within lifeforms over time - not the origin of life itself. I would object to their position, but suffice to say that logic does allow them to hold it.
Now, what does science say about the origin of life? Again, evolutionists avoid this question. The truth is that science has never observed any possible natural mechanism for the origin of life in the universe. Every honest scientist will admit this to you. The origin of life is a complete and total mystery to scientists. Although they will jump to provide all their biological and cosmological theories whenever someone asks about the origin of life and the universe, when pressed about the specific question regarding the process by which the first lifeform came into existence, they will admit that their theories do not speak on this specific question. And in truth, science is actually incapable of speaking to this question.
Science is limited to empirical observation. Science, by its very definition, is based upon observation and experimentation. So, even if we knew where to look in order to observe the process of 'abiogenesis' to occur, all we would be left with is the observation of the miraculous event whereby some non-living matter would suddenly gain personal intelligence, intentional function, and life within itself. There is no way in which abiogenesis (the creation of life from non-life) could ever be explained scientifically, even if a person witnessed such a miraculous event. The arrival of life is supernatural. Non-living matter does not just come alive, no matter how much non-living matter is mixed with it, and no matter how long we allow for the non-living matter to mix around together. The moment life arises is supernatural and beyond scientific explanation.
Some scientists have tried to explain this away by saying that maybe the first lifeform was planted here on earth by a super intelligent alien species from a distant galaxy. They offer up this as an explanation because 1) they recognize that there is absolutely no mechanism for life to occur naturally, 2) they recognize that the quality and characteristics we observe in all lifeforms are such that they could have only came about through design - and the design is something far, far beyond our own intelligence's capabilities. But what they fail to recognize is that attributing the origin of life on earth to aliens is simply "kicking the can down the road." The question remains completely unanswered, we have only moved the origin from earth to some distant unknown planet. Maybe, these scientists hope, the conditions are different elsewhere in the universe. Maybe the amount of heat, water, and organic minerals are different on the planet the aliens come from, and maybe those differences make their planet more conducive to abiogenesis than our own. But what they fail to recognize is that - no matter what the material conditions - life does not arise from non-living matter.
Life is a metaphysical, transcendent reality. Consciousness, intentional personal behavior, feelings and emotions, and especially the reasoning faculty - these are all realities that far exceed anything the material world could generate on it's own. A transcendent, metaphysical force is required.
So whats the origin of humanity? Well, whats the origin of life? If a person were to reject the premise that life requires transcendent, metaphysical causation, then they would not be able to offer any meaningful answer. For such a person the answer to any and every question about how things happen is "they just do." Without reference to an ultimate, transcendent, eternal, metaphysical reality behind the universe, a person cannot answer questions about how things happen. They can only observe things happening. As to why something happens instead of nothing happening, they cannot say. All they know is that they observe things happening. They cannot say anything regarding the nature of how they actually do happen. So we are only left with two choices: we can choose to believe that there is no ultimate mechanism determining how things happen, or we can recognize that as living beings we have been given life from life itself. Life comes from life, and the existence of life requires life. Therefore, the source of life is eternal and dependent on no one and nothing but itself. The source of life is eternal, is life itself, and is completely independent of all other things. And it is greater than all things, infinitely greater, to the extent that all created things - whether living or non-living - are mere creatures and were brought into existence by Him.
He is God. And He revealed Himself to us. He chose to empty Himself and become a human being in order to live among us, teach us about Himself, and win for us our redemption from evil. Going to the cross, allowing Himself to be brutally tortured to death on our behalf, He also opened Himself up to every bit of darkness and evil that exists in the universe. Every perverse and wicked temptation, every evil creature who has perverted the life that God gave them and turned themselves in God's enemies, every form of sin and suffering in existence... On the cross, while in extreme physical agony, Jesus allowed all these things to surround and attack Him, to try with all their might to seduce Him, to make Him suffer, to darken Him and bring about His destruction. And Jesus endured that agony, both spiritual and physical, and in doing so He swallowed up and destroyed all the wickedness that sought to take advantage of Him in His weakness. In His infinite love and mercy, God entered into the heart of evil, and of course God did not let evil invade Him in anyway, but rather, God invaded evil, and His infinite love and mercy swallowed it all up, and destroyed it, like a sponge He soaked up all of our sin so that we would not have to bear it's weight, and He cast it all out, destroyed it in eternal fire and outer darkness, never to be seen again. Although the source of life had given us our own life, and although we responded with wickedness and not gratitude, and although we chose to make ourselves His enemy instead of walk with Him as friends, yet God in His infinite love and mercy towards us chose to suffer unthinkable agony on our behalf, becoming our Savior.
The source of life, then, is for us also the source of new life; and the source of eternal life. Though we may suffer death in our physical bodies, those of us who enter into God's love and mercy will be given new bodies, and we will live forever with Him in a new world free from all pain and suffering, free from all sin. The source of life will become for us our deeply personal source of life, not just in an ultimate metaphysical sense, but through direct personal relationship. He is God, and if we choose we can invite Him to come into our life and take His rightful place as God, and if we enter eternity with Him as our God then He will become our God forever in the most comprehensive and beautiful way possible. He is the only God, there is no other, but for sinful human beings He is often times an object of non-acknowledgement. Due to sin, He becomes distant from us. It is possible for a person to live their whole life never knowing Him. But He is there for those who desire to know Him.
For those who seek understanding, for those who want to know about the origin and meaning of life, and for those who seek this knowledge with sincerity and an open heart, God will make Himself known. Science is limited in this regard. Science cannot observe and thus cannot enter into the realm of metaphysics. Metaphysical pursuits are outside the realm of science, and scientists who limit themselves to science alone are limiting themselves from the pursuit of metaphysical truth. The scientist will never be able to speak on the origin and meaning of life unless he first cast away the empirical prejudice and becomes a philosopher. The origin of life is a philosophical question, a metaphysical question, and it appears that many fail to understand this important distinction. As if the answer to this question can be found by looking through microscopes and telescopes, people look to the ground and to the sky in order to find what can only be found by looking in their hearts and looking in their minds.
"You shall seek me, and shall find me: when you shall seek me with all your heart."