Darwin would certainly have changed his theory if he had known about genetics i.e. he would have known the source of the variation upon which natural selection operates and how it is spread from generation to generation...i.e. he could have scooped the geneticists of neo-darwinism by about 60-70 years.
As to knowing how complex nature can be, that was obvious long before Darwin's time and does not require incorporation of the supernatural to explain it...in fact, nothing in science benefits from incorporating or postulating mythical supernatural causes.
I don't think knowing Mendel's work would have helped Darwin much. Just look at the mess it caused at the turn of the century. What genetics did for Darwin wasn't apparent until the 1920's and 30's, when Fisher, Haldane and Wright showed how selection acted on genes in populations. By showing that even slight selective advantages could produce significant changes in the genetic structure of populations over time, Darwin's idea of gradual change was saved from being thrown out altogether.
Observation 1: Most individuals produce far more offspring than is needed to replace themselves.
Conclusion 1: Most individuals must die without reproducing.
Observation 2: In any population, there is a wide range of variation.
Assumption 1: Those individuals that survive and reproduce will be the ones whose characteristics make it more likely that the individual will survive.
Observation 3: Much of this variation is hereditary.
Conclusion 2: This "natural selection" will cause certain characteristics to decrease in frequency, perhaps even disappear completely; and cause other characteristics to increase in frequency, perhaps to become evident in every member of the population.
Observation 4: Humans have bred many varieties of plants and animals with characteristics that are not observed in the wild ancestral species.
Conclusion 3: There is a source of new heretable characteristics.
Conclusion 4: The production of new characteristics with natural selection will cause a species to undergo a tremendous amount of change over very long time periods.
Observation 5: For each domesticated species, humans have bred a large number of different breeds.
Observation 6: Life can be classified in a heirarchical system.
Conclusion 5: All current (and known past) species evolved from a small number of, perhaps only a single, ancestral species.
Note that there is no assumption whatsoever about the structure of the cell, or even that organisms are composed of cells.
Darwin looked at the structure of change in populations (which is what the Scientific Theory of Evolution is all about). He didn't know about genes, as the DNA and genes weren't discovered until a long time after his death. Darwin's theory stands on the observations of his day. If he knew more of the research that has been done since, he would have been able to expand on his model, but it wouldn't have changed much.
This is like asking if the Wright Brothers would have changed their idea about flight if they had known about the jet engine. They would have been able to build a bigger, stronger plane, that's all; they would not have changed the idea of flight of the basic processes of flight. On the other hand, the Wright brothers writings are not closely consulted when designing space shuttles; we don't have to worry about whether flight is possible. It is kind of the same with Evolution. Science looks at the new information, not the stuff that has long ago been established because it already have been proven many times.
Darwin did deal with macroscopic complex systems, namely the mammalian eye. He was amazed at the complexity of the organ, but he found that every step of eye evolution was present in living organisms, starting with a photosensitive spot right up to a lensed eye with a retina. He felt that evolution does address complexity, and explains it well in that evolution would add layers to already existing systems, therefore building up complexity over time.
Perhaps not Mendel's work specifically, but if he had known of genetics and DNA as the mode of transmission of variation, it would have filled in some gaps. However, it would not have changed his theory.
quote:Perhaps not Mendel's work specifically, but if he had known of genetics and DNA as the mode of transmission of variation, it would have filled in some gaps. However, it would not have changed his theory.
Watching the various posts within this site makes me question peoples knowledge of Darwins own theory. I've talked to many people who call themselves evolutionist and try to site Darwin without even reading for themselves what his theory really was. Again, most of the people who are oppose creation have not even read the Bible. To be fair, I have talked to many Creationist who have not read the Bible nor any of Darwin's works. Which animals did GOD create? What was Darwins thoughts in the last few chapters of "The Origin Of Speicies"? And no, the condensed version of either the Bible nor the Origin of species is not allowed. Too many things were removed from both. To answer the question posted: Darwin did change his own theory within his own works. Being an outstanding Naturalist, I'm sure he would have changed alot of ideas knowing what we do today!