Darwin developed the theory of evolution to explain why there are so many different kinds of living things. He could easily observe that offspring of any animals were slightly different from their parents and that this could allow for big changes over thousands of years. He did not know that genes caused the differences. Genes are now very important in the modern theory of evolution.

What most likely led to a change in the widely accepted theory of evolution?

new experiments involving genes and evolution
experiments with Darwin’s original hypotheses
changes that Mendel made to his laws of genes
studies of evolution without Mendel’s laws