What part of darwin's natural selection theory couldn't he explain? whose work was discovered after darwin's death to fill gaps in his theory? people lease

 Back in Darwin's day, they didn't know anything about Genetics.

Gregor Mendel is usually considered to be the founder of modern genetics. Though farmers had known for centuries that crossbreeding of animals and plants could favor certain desirable traits, Mendel's pea plant experiments conducted between 1856 and 1863 established many of the rules of heredity.

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