Crossword Genius

Insect demonstrating natural selection (4)

Ross

I believe the answer is:

gnat

I'm a little stuck... Click here to teach me more about this clue!

'insect' is the definition.
(gnat is a kind of insect)

'demonstrating natural selection' is the wordplay.
'GNAT' is hidden within the letters.
However, I am unsure how this is indicated.

Can you help me to learn more?

(Other definitions for gnat that I've seen before include "Two-winged fly" , "mozzie" , "Small biter" , "annoying flier" , "Small fly that bites" .)

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