flagella

I suspect the answer is that having flagella without a nose is still better than having no flagella.

A flagella is only useful as a component of something, but not by itself.

I mean there are so many amazing things like ATP generating machinery, how flagella move, ribosomal walking etc.

Stated clearly (0) has recently started a fantastic series about evolution that aims to explain bacterial flagella.

The bacterial flagella and the rotating enzymes, which are powered by ionic currents, cannot be scaled to greater sizes.

In this particular case, cells have many molecular pumps, so converting some to flagella is not a very big problem.

There are many such captures, for example the cilia of ciliates or the flagellum of flagella.

Think of the neural complexity required for an amoeba to navigate with flagella vs a fly to navigate with wings.

No no no hang on, I mean flagella based molecular motors!

One mutation gives you a bit of a flagella, another gives you bit of a nose, but how does the flagella mutation survive to coexist with the nose mutation that makes it useful.

In your case, why would a flagella be useful if it's not propelling something?

In an unicellular organism, a part of the cell senses light and another part, like flagella or contractile filaments reacts, moving the cell.

Lynn Margulis’s work also suggests that structures like cilia and flagella, that seem like integral parts of the cell, are actually “captured” symbionts that used to be independent organisms.

For instance it says "In eukaryotes, adding cilia or flagella does not increase motility, nor does increasing cell size lead to a major increase in velocity", which is false and the article itself contradicts immediately this sentence by writing "Ciliates are much faster than flagellate eukaryotes".

Flagella are complex structures that did not arise until after a lot of other things had already developed.

Flagella only exist as components of something, they do not need to and shouldn't exist by themselves.

Flagella are true rotating motors with stators, rotors, bearings, and torque generation via ion gradients.