Larson 7

At the time Darwin wrote Origin of Species scientists assumed that offspring inherited a mix of the characteristics of their parents
but evolution by natural selection of small variations does not work if that is the case, because the variations will be drowned out

Darwin's cousin Francis Galton promoted Eugenics: use selective breeding to improve the human raceinheritance of blood types
chromosomesScientists started to try to pin down hard heredity

Hugo de Vries was one of several scientists who started looking for sudden mutations
inheritance in pea plants
source for more explanation
Two other botanists also claimed to have independently rediscovered Mendelian genetics, but Mendel gets credit because he actually laid out the theory fairly completely

You need both mutations and Mendelian genetics to be able to show mathematically that evolution works, but they were separate theories and people put them together in different ways.  There were a lot of mixed theories: including or not including natural selection, seeing genes as immaterial or located on chromosomes

Thomas Hunt Morgan proved that genes are on chromosomes (early 1910s)

We still haven't gotten to the Modern Synthesis, of genetics and Darwin's theory of evolution by natural selection of small variations

morgan's fruit fly research