This is a very interesting guest post at Remote Central:
All species vary through time and space. You don't necessarily look the same as any one of your ancestors. Therefore "like begets like" but each individual can be a bit different. It is impossible for a sperm whale to evolve from a bowl of petunias, or a duck from a dandelion, as some creationist and Intelligent Design supporters accuse evolutionists of believing. But over time it is possible for a cow to evolve from something like a camel, or a human to evolve from something like an ape. Evolution doesn't proceed in a straight line though, especially not a straight line with a human at the end.
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News to me that female ducks have Y chromosomes. Did a little looking online in the literature and could find no mention of a Y chromosome in mallards.
The XX = female XY = male is mammalian. Birds have something that could be referred to as XX = male, XY = female.
Actually, for any given species, there is a straight line back through its ancestry. That doesn't give the complete picture of evolution, however, and that's what's important.