It isn't completely blind, it runs via very very minor advantages, that is each generation shows a 0.0001% better survival for a certain trait, over a million years that adds up to a new species, or two different species( because the difference is not strong enough for the other to fail).
The thylacine is an example of divergent eveolution, like the hedgehog and the Madagascan Tenrecs.
but what advantage would say,some creature halfway between a wallaby and a thylacine have(granted australia is a niche rich environment and isolated)..personally id say hormones could play a big part--m