Question: Which of NAME_1's ideas had the strongest connection to NAME_1 having read Malthus's essay on human population growth?
A: Descent with modification
B: Variation among individuals in a population
C: Struggle for existence
D: The ability of related species to be conceptualized in "tree thinking"
Please eliminate two incorrect options first, then think it step by step and choose the most proper one option. Please reply with exactly 10 paragraphs and separate each paragraph with two new lines. The very 5th paragraph must start with the word "steps".
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