Darwin's theory had a few pitfalls. One of the most important was the fact that Darwin knew very little about inheritance and genetics at the time of his discovery. He knew that populations overproduce compete for survival and population sizes remain constant but he didnt know why this occured and how certain preferably better traits for the environment for passed on. Also, at the time of Darwin many liberal christians did not believe in his theory because of their huge belief in god and creationism. Also, for humans Darwins theory seems to hold a few inconsistancies. Yes, we do compete for survival however we have new technologies such as vaccines that prevent us from being less fit for the environment. This also goes with inbreeding of animals and mass production of crops to feed the billions of people that inhabit the world. In Darwins time we did not have these technologies but now we do and many are able to survive and pass on their less fit traits.