Which geologist friend of Darwin helped arrange the joint presentation with Wallace?

Charles Lyell was the geologist friend of Darwin who helped arrange the joint presentation of Darwin’s and Wallace’s ideas on natural selection. Lyell had encouraged Darwin to publish after Alfred Russel Wallace sent Darwin an essay in 1858 outlining a theory strikingly similar to his own.

Darwin was reluctant to claim priority, especially because Wallace’s essay had arrived before Darwin had formally published his theory. Lyell and the botanist Joseph Dalton Hooker therefore helped organize a joint presentation to the Linnean Society of London. On 1 July 1858, papers by Darwin and Wallace were read together, establishing a respectful shared-priority arrangement.

A common mix-up is crediting Lyell alone. Hooker played an equally important practical role, including helping prepare Darwin’s material for presentation. Lyell’s role is the canonical answer here because the question identifies Darwin’s geologist friend; Hooker was primarily a botanist and plant geographer.

Lyell’s geological work also influenced Darwin deeply. His principle of uniformitarianism argued that gradual processes operating in the present could explain vast changes over immense spans of time, giving Darwin an essential framework for thinking about evolution.