The theory of evolution

In his book On the Origin of Species by Means of Natural Selection, Charles Darwin wrote that creatures experience genetic mutations prior to birth. Some of these random mutations are beneficial, and some are harmful. He wrote that in the world, the creatures who are the "most fit" are most likely to survive and then later pass on their genes. This process, known as natural selection, results in the strongest creatures thriving and the weak dying off.
One of the biggest results of Darwin's theory of evolution was that it was another major challenge to the Catholic Church. This, combined with the previous Reformation, Renaissance, the Enlightenment, and other related movements, caused the Church to lose even more influence in society. Also, Darwin's theory led to the rise of the concept of social Darwinism, or "survival of the fittest." This theory is still used today in the science community and in the classroom.