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Genes aren't the only inherited trait. Environment, wealth, culture, and ideas are also roughly passed down to offspring, but these can't modify the genome, only the gene expression.
Of course it gets way more complex as these things do change fitness which does apply evolutionary pressure to the genome, but you can't get bigger muscle genes by working out.
That is to say, there are some Lamarckian effects, but it's all by Darwinian mechanics.