The sentence that best helps develop the idea expressed in paragraph 2 is:
"Thanks to this analysis, the researchers were able to narrow down their original list of 3,000 genes to 43 specific sequences that might have contributed to Lonesome George’s long, disease-free life."
This sentence directly relates to the researchers' efforts to understand genetic factors contributing to longevity, as described in the analysis of Lonesome George and other giant tortoises.