Convergence generally happens as a solution to a general technical problem which can be arrived at through a series of small adjustments.
For instance if the species moves in a fluid streamlining will develop by itself because those who are more streamlined move faster.
If you have an advantage from eyes, a hemisphere of light sensors behind a lens which can change shape is a solution that comes about naturally (there are other solutions to the problem).

If you have a predator/prey pair where the prey is armored against most things and the predator develops weapons to take it down, you'll get the escalating arms race of prey getting ever more armor and predators getting ever bigger and more specialized weaponry until the prey becomes too slow to survive at which point both species go extinct, this has happened at least 6 times on earth.

Lots of things like those are bound to be repeated, but a lot of traits are incidental, results of the first random differences.

Legs seems to be a general solution to motion as they have been developed independently many times, how they are put together and how many to have is not.

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‘To those who regard “crime fiction” as some sacred icon which must follow a rigid formula, I will always be the man who writes 18-syllable haiku.’Trying to make sense of computers, The Error Log.