The human race, a certainty to include tip-top staff (6,3)

I believe the answer is:

mortal man

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

'a certainty to include tip-top staff' is the definition.
I don't know anything about this answer so I can't judge whether this works.

'the human race' is the wordplay.
'the human' becomes 'mortal' ('mortal' can be a synonym of 'human').
'race' becomes 'man' (I've seen this before).
'mortal'+'man'='MORTAL MAN'

Can you help me to learn more?

I've seen this clue in the Sydney Morning Herald.

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