Excessive amount found by academic about The Origin of Species ? That's probable (4-2)
I believe the answer is:
odds-on
'probable' is the definition.
(thesaurus)
'excessive amount found by academic about the origin of species ?' is the wordplay.
I cannot really see how this works, but
'amount' could be 's' (S is an example) and 's' is found in the answer.
'academic' could be 'don' (type of academic - especially at Oxbridge) and 'don' is present in the remaining letters.
'of' could be 'o' and 'o' is found within the answer.
A single letter 'd' remains which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
'that's' acts as a link.
Can you help me to learn more?
(Other definitions for odds-on that I've seen before include "High probability" , "With success more likely as bookie would calculate" , "With favourable chances" , "With success more likely than favour in bookie's phrase" , "More likely to win than lose" .)