Things change. The communist government championed a horticulturist named Lysenko, who embraced a form of Lamarckianism. Before Darwin Lamarck supposed that creatures changed by the inheritance of acquired traits. If you spend a lot of time running and develop strong leg muscles and lungs, then Lamarck thought that your baby would inherit these traits developed during your lifetime. This idea was in direct opposition to Darwin's theory of evolution, which said that populations contain a lot of variation and this variation is passed on to the offspring without modification. The change over time comes from natural selection filtering the variants, resulting in higher reproductive success for some variants than others.
Of course in Darwin's time the details of inheritance were not known. Mendel published his work on inheritance then, but it was not well known until after his death. When Mendel's work was rediscovered geneticists realized that inherited traits were passed on in genes (although at the time they still didn't know what genes were!) Geneticists started working with plants, breeding them and studying their chromosomes.
It's hard to say why the communist government found Lysenko's ideas so appealing, perhaps because he was their representative of the "common man" who had arisen and thrown over the ideas of bourgeois foreigners. At any rate Mendelian genetics went far far out of favor, and geneticists who didn't abandon their evolutionary ideas and embrace Lysenkoism were imprisoned and even killed.
Perhaps for the same reasons that Haldane found Lysenko so appealing. He was a shill for Lysenko, you know. Haldane, Darwin Medalist and co-founder of the Modern Synthesis.
Marx said that everything about a human being is determined by his social class. Therefore, it was unwise to talk too much about chromosomes in Lysenko's time.
If you spend a lot of time running and develop strong leg muscles and lungs, then Lamarck thought that your baby would inherit these traits developed during your lifetime. This idea was in direct opposition to Darwin's theory of evolution
I'm sorry but that's complete nonsense, as Darwin was not opposed to this notion at all. Darwin was a "lamarckian" in this sense whenever it suited him to be so. It was Lamarck's other idea, entelechy or whatever he called it, that Darwin didn't like.