1798 Malthus publishes paper on population growth. Malthus noticed that the human population was expanding exponentially. He thought that the human population would outgrow its resources and that this would lead to famine and war.
Darwin was influenced by this idea, because he noticed that animal populations grow exponentially and then plateau when they reach the limits the environment can sustain (i.e. the population size is determined by the environment)
1809 Lamarck publishes a mechanism for evolution based on two laws
Law 1: Organs / structures grow if they are used. This means that the environment determines the phenotype of an organism
Law 2: Changes are passed on to the next generation
So a blacksmith, who uses his muscles all day, will grow bigger muscles. This works! But, will the bigger muscles be passed onto his children? No, so Lamarck’s theory is easy to falsify.
1859 Darwin publishes the Origin of species by means of Natural Selection. He publishes with Wallace who wrote to Darwin to discuss his own ideas about evolution. They were very similar to Darwin’s and this prompted Darwin to publish.