Q.Darwin's original theory could explain how favourable variations are selected but could not explain how heritable variation itself arises in the first place. How does the modern synthetic theory address this gap?

Step 1. Darwin's theory explained how favourable variations spread through selection but not how variation itself originates.

Step 2. Darwin worked before Mendel's genetics was widely known (rediscovered in 1900, after Darwin's 1882 death) and held a vague, largely incorrect 'blending inheritance' view.

Step 3. The modern synthesis incorporates Mendelian and molecular genetics, identifying mutation (new DNA sequence changes) and recombination (reshuffling of existing alleles) as the actual sources of heritable variation. …

Identify exactly what Darwin's theory was missing (a correct mechanism for the ORIGIN of variation), then s …

• Suggesting Darwin himself proposed mutation/recombination (he did not; these are genetics-era concepts added later). …