It is very sad to see someone like Charles Darwin descend into darkness. It appears that, as a young man, Charles Darwin had faith in Jesus, although he was not mature in that faith. This illustrates the danger that exists when we turn over the training of our children to ungodly men and women.  

The Quotes:  

I often had to run very quickly to be on time, and from being a fleet runner was generally successful; but when in doubt I prayed earnestly to God to help me, and I well remember that I attributed my success to the prayers and not to my quick running, and marvelled how generally I was aided. ~ Charles Darwin as a young man  
 
I liked the thought of being a country clergyman. Accordingly I read with care Pearson on the Creed and a few other books on divinity; and as I did not then in the least doubt the strict and literal truth of every word in the Bible, I soon persuaded myself that our Creed must be fully accepted. ~ Charles Darwin  
 
I could have written out the whole of the 'Evidences' with perfect correctness, but not of course in the clear language of Paley," and, "I do not think I hardly ever admired a book more than Paley's 'Natural Theology.' I could almost formerly have said it by heart. ~ Charles Darwin at the seminary  
 
During these two years [OCTOBER 1936 to January 1839] I was led to think much about religion. Whilst on board the Beagle I was quite orthodox, and I remember being heartily laughed at by several of the officers (although themselves orthodox) for quoting the Bible as an unanswerable authority on some point of morality. I suppose it was the novelty of the argument that amused them. But I had gradually come by this time, i.e., 1836 to 1839, to see that the Old Testament from its manifestly false history of the world, with the Tower of Babel, the rainbow at sign, &c., &c., and from its attributing to God the feelings of a revengeful tyrant, was no more to be trusted than the sacred books of the Hindoos, or the beliefs of any barbarian. The question then continually rose, before my mind and would not be banished, is it credible that if God were now to make a revelation to the Hindoos, he would permit it to be connected with the belief in Vishnu, Siva, &c., as Christianity is connected with the Old Testament? This appeared to me utterly incredible. ~ Charles Darwin, speculations in his autobiography on God religion and religious belief (Darwin had heard the philosophies of the age, but didn't know the answers to the speculative skepticism regarding the Bible. It's a shame that the skeptics didn't have the same skepticsm toward the skepticism.)  
 
... the Gospels cannot be proved to have been written simultaneously with the events, that they differ in many important details, far too important, as it seemed to me, to be admitted as the usual inaccuracies of eyewitnesses; by such reflections as these, which I give not as having the least novelty or value, but as they influenced me, I gradually came to disbelieve in Christianity as a divine revelation. ~ Charles Darwin, speculations in his autobiography on God religion and religious belief (These statements of Darwin have since been proved false.)  
 
... disbelief crept over me at a very slow rate, but was at last complete. The rate was so slow that I felt no distress, and have never since doubted even for a single second that my conclusion was correct. ~ Charles Darwin, confession in his autobiography on God religion and religious belief  
 
Although I did not think much about the existence of a personal God until a considerably later period of my life, I will here give the vague conclusions to which I have been driven. The old argument from design in Nature, as given by Paley, which formerly seemed to me so conclusive, fails, now that the law of natural selection has been discovered.  We can no longer argue that, for instance, the beautiful hinge of a bivalve shell must have been made by an intelligent being like the hinge of a door by man. There seems to be no more design in the variability of organic beings, and in the action of natural selection, than in the course which the wind blows. ~ Charles Darwin, speculations in his autobiography on God religion and religious belief (Natural selection, of course, has no ability to create new genetic material. It can only make the genetic mistakes that are more severe extinct. Of course, Darwin didn't know anything about this. He thought there was such a thing as a simple cell.)  
 
Some writers indeed are so much impressed with the amount of suffering in the world, that they doubt, if we look to all sentient beings, whether there is more of misery or of happiness; whether the world as a whole is a good or bad one. According to my judgment happiness decidedly prevails, though this would be very difficult to prove. ~ Charles Darwin, speculations in his autobiography on God religion and religious belief (This misunderstanding of suffering is quite common.)  
 
That there is much suffering in the world no one disputes. Some have attempted to explain this with reference to man by imagining that it serves for his moral improvement. But the number of men in the world is as nothing compared with that of all other sentient beings, and they often suffer greatly without any moral improvement. A being so powerful and so full of knowledge as a God who could create the universe, is to our finite minds omnipotent and omniscient, and it revolts our understanding to suppose that his benevolence is not unbounded, for what advantage can there be in the suffering of millions of the lower animals throughout almost endless time? This very old argument from the existence of suffering against the existence of an intelligent First Cause seems to me a strong one; whereas, as just remarked, the presence of much suffering agrees well with the view that all organic beings have been developed through variation and natural selection. ~ Charles Darwin, speculations in his autobiography on God religion and religious belief (This misunderstanding of suffering is quite common.)  
 
At the present day the most usual argument for the existence of an intelligent God is drawn from the deep inward conviction and feelings which are experienced by most persons. But it cannot be doubted that Hindoos, Mahomadans and others might argue in the same manner and with equal force in favour of the existence of one God, or of many Gods, or as with the Buddhists of no God. There are also many barbarian tribes who cannot be said with any truth to believe in what we call God: they believe indeed in spirits or ghosts, and it can be explained, as Tyler and Herbert Spencer have shown, how such a belief would be likely to arise. ~ Charles Darwin, speculations in his autobiography on God religion and religious belief  
 
Formerly I was led by feelings such as those just referred to (although I do not think that the religious sentiment was ever very strongly developed in me), to the firm conviction of the existence of God, and of the immortality of the soul. ~ Charles Darwin, confessions in his autobiography on God religion and religious belief  
 
Another source of conviction in the existence of God, connected with the reason, and not with the feelings, impresses me as having much more weight. This follows from the extreme difficulty or rather impossibility of conceiving this immense and wonderful universe, including man with his capacity of looking far backwards and far into futurity, as the result of blind chance or necessity. When thus reflecting I feel compelled to look to a First Cause having an intelligent mind in some degree analogous to that of man; and I deserve to be called a Theist. This conclusion was strong in my mind about the time, as far as I can remember, when I wrote the 'Origin of Species;' and it is since that time that it has very gradually, with many fluctuations, become weaker. But then arises the doubt;-- can the mind of man, which has, as I fully believe, been developed from a mind as low as that possessed by the lowest animals, be trusted when it draws such grand conclusions? May not these be the result of the connection between cause and effect which strikes us as a necessary one, but probably depends merely on inherited experience? Nor must we overlook the probability of the constant inculcation in a belief in God on the minds of children producing so strong and perhaps an inherited effect on their brains not fully developed, that it would be as difficult for them to throw off their belief in God, as for the monkey to throw off its instinctive fear and hatred of a snake. ~ Charles Darwin, confessions in his autobiography on God religion and religious belief  
 
What my own (religious) views may be is a question of no consequence to any one but myself. But, as you asked, I may state that my judgment often fluctuates.... In my most extreme fluctuations I have never been an Atheist in the sense of denying the existence of a God. I think that generally (and more and more as I grow older), but not always, that an Agnostic would be the more correct description of my state of mind. (F. Darwin 1888, I: 304;).  
 
What my own views may be is a question of no consequence to any one but myself. But, as you ask, I may state that my judgment often fluctuates. ... In my most extreme fluctuations I have never been an Atheist in the sense of denying the existence of a God. I think that generally (and more and more as I grow older), but not always, that an Agnostic would be the more correct description of my state of mind.~ Charles Darwin (ed.) 1887. The life and letters of Charles Darwin, including an autobiographical chapter, Vol. 1, p. 304. London: John Murray.