This article breaks down how the cell behaves down the the molecules. Once each part is pulled apart and examined, where did the 'intelligence' go.
The single cell, looks 'intelligent'. But, when it is all pulled apart we don't find it. It is just chemicals, reactions, physics.
Then, scale that up to multi-cellular organism, then human, its all just mechanistic, chemicals, physics. So where did the intelligence come from? Humans are also just twitching flagella.
This article just makes it a more stark idea, because a single cell appears 'intelligent', but we can pull it apart and examine the constitutive parts, the chemical, molecules.
So there is not much wiggle room for philosophy or souls. It looks intelligent, but look, we can peer under a microscope and don't see the intelligence.