Final answer:
Darwin delayed publishing his theory due to conflicts with religious beliefs, the desire to gather ample evidence, and concerns over Earth's age. He published after Alfred Russel Wallace independently developed a similar theory.
Step-by-step explanation:
There are three main reasons why Charles Darwin waited so long to publish his theory of evolution by natural selection. Firstly, Darwin's ideas were at odds with the prevailing religious beliefs of the time, which posited that species were immutable and did not go extinct, and that the Earth was about 6,000 years old. Secondly, Darwin wanted to amass compelling evidence to buttress his theory. Over twenty years, he meticulously analyzed specimens, engaged with other scientists, and assimilated additional information to substantiate his assertions.
Lastly, Darwin was influenced by the scientific context of his era, including concerns over the age of the Earth and the Sun. The implications of his theory required a much older Earth than contemporary theories suggested, and these discrepancies caused him trepidation. It wasn't until Alfred Russel Wallace independently formulated a similar theory of evolution that Darwin was compelled to finalize and publish his landmark work, On the Origin of Species in 1859.