Darwin had no idea of the complexity of cellular biology. It is fantastically complex. This is why noted atheist Anthony Flew recently switched sides in the debate and now believes that the universe and life can only be reasonably explained by intelligent design:
"The second [reason for belief in ID]was my own insight that the integrated complexity of life itself which is far more complex than the physical Universe can only be explained in terms of an Intelligent Source. I believe that the origin of life and reproduction simply cannot be explained from a biological standpoint despite numerous efforts to do so."
http://www.tothesource.org/10_30_2007/10_30_2007.htm
Which is why it's fantastic that, without any knowledge of genetics or cell biology, Darwin nevertheless got it right. What's amazing is how right he was, given how little information he had access to. Today we understand how evolution's course is writ across the genome.
This is why noted atheist Anthony Flew recently switched sides in the debate and now believes that the universe and life can only be reasonably explained by intelligent design:
Flew is a philosopher of religion, not a scientist. Try again.