Charles Darwin is credited with the evolutionary theory, but his knowledge was influenced by many great scientists of his time. In my opinion, Thomas Malthus had the largest, positive influence on Darwin's theory development for a few reasons. Malthus' book, An Essay on the Principle of Population, pointed out the fact that although population sizes increase, the amount of resources tend to stay the same. He was, in fact, focusing more on humans, but Darwin expanded this thought to all organisms. Malthus showed the science community, including Darwin, that competition is constantly present when population size is restricted by the mount of resources available (https://www.allaboutscience.org/malthus-faq.htm). Malthus was able to prompt Darwin to realize that the number of offspring produced in a species were more than the number that was meant to survive.
The bullet point Who gets better access to these limited resources? was most influenced by Thomas Malthus. It states that the organisms that are better adapted to their environment are more competitive. Malthus found that resources stayed at a constant capacity, but those that knew how to deal with the issues in a smarter way were ultimately more competitive and would survive longer. Darwin took this idea and centered his entire evolutionary theory around it. The survival of the organisms best adapted to their environment was the basis of natural selection. In fact, I don't believe that Darwin would have developed the theory of evolution without Malthus' discoveries and insights. Because Malthus came up with "the survival of he fittest," Darwin was able to elaborate on it and clarify how that related to the evolution of organisms over time.
Darwin was reluctant to publish his theory for the world to see, partly because he knew how controversial it would be, especially within the church. The ideas within evolutionary theory go against what many religious groups believe in, and people at this time did were concerned with going against the norm. Darwin finally decided to publish his findings after realizing that Alfred Russell Wallace might get credit instead.
