One of the most revolutionary ideas and treatises. He was an avid naturalist. He took advantage of a remarkable opportunity and came face to face with contrasts that challenged his assumptions. Struck by dramatic differences between England and South America, the fossils of old species and of shellfish in the 'wrong' places. Most populations are stable.
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Therefore, there is a struggle for existence among individuals in a population 4. Accumulated ever since and confirmed his suppositions, elevating the hypothesis to a Theory. However, these difficulties do not challenge the theory, rather they suggest that we should keep an open mind about some of the minor assumptions of mechanism. Pace of evolution remains controversial. Some feel the development of species wasn't so gradual and advanced a theory known as punctuated equilibrium where Eldredge and Gould proposed that morphological leaps were made over time.