For once, I agree with torridon. At least, not in any spiritual sense. On the other hand, I think that genetics can provide some degree of 'destiny' - if one has a genetic condition, it is likely that any natural children you have might will inherit it and the 'destiny' associated with that.
I agree destiny is a bit dicey...especially if you are religious and believe in God, free will, right and wrong, reward & punishment etc.
Scientists find it easier to believe in predetermination because everything to them is just laws of physics. Life works like a machine... on and on. No external intervention. Once the ball gets rolling it goes on in accordance with the laws.
I believe in karma, reincarnation and spiritual development. I believe that the physical is only a product of the spiritual. How this fits in with destiny is a bit difficult to put together.
Karma itself is destiny in a sense...and what HH talks of epigenetics is also valid here. Everything has an effect, a reaction and a consequence. This is destiny.
I believe life is like a VR computer game. Everything in the game is fixed....but you can still win or lose. As you keep doing the right things you keep progressing to higher and more complex aspects of the game.....rules become tighter and more intricate. If you lose you keep repeating the game.
This idea has room for destiny, freewill, karma, equality, individual development and progression....and also a smart game designer.