> but a dog will never produce a non-dog, and a fish will never produce a non-fish. This requirement of microbe-to-man evolution contradicts the fundamental law of heredity.
Agreed! And doing so would of course invalidate our current understanding of how evolution works! We'd have to throw out our theory of evolution by natural selection if we ever observed a dog give birth to a non-dog!
The definition of a "species" isn't something defined by nature. Rather it's a construct that humans invented in our need to categorize things. Genetic dissimilarities one generation to the next are of course very very small. So small that adjacent members will always be of the same "species" (able to breed with each other). But cumulative changes over generations add up. So much so that if we skipped ahead many generations, we'd no longer have compatible breeding. Different "species" as we would say under our admittedly flawed categorization system. At what point in the family tree does the species change? Given that each species can breed with its adjacents? At what point does a color gradient stop being red and start being blue? As you can see, the flaw in this understanding stems only from holding onto the definition of distinct "species" as something real rather than a human creation. A useful one, don't get me wrong! But it's important to understand the fuzziness of this definition. Your argument stems from a fundamental misunderstanding of this idea.
By the way, the example above is not merely hypothetical, since species can be separated in space as well as time. We can observe this phenomenon in action through very fascinating phenomenon like "ring species".
Agreed! And doing so would of course invalidate our current understanding of how evolution works! We'd have to throw out our theory of evolution by natural selection if we ever observed a dog give birth to a non-dog!
The definition of a "species" isn't something defined by nature. Rather it's a construct that humans invented in our need to categorize things. Genetic dissimilarities one generation to the next are of course very very small. So small that adjacent members will always be of the same "species" (able to breed with each other). But cumulative changes over generations add up. So much so that if we skipped ahead many generations, we'd no longer have compatible breeding. Different "species" as we would say under our admittedly flawed categorization system. At what point in the family tree does the species change? Given that each species can breed with its adjacents? At what point does a color gradient stop being red and start being blue? As you can see, the flaw in this understanding stems only from holding onto the definition of distinct "species" as something real rather than a human creation. A useful one, don't get me wrong! But it's important to understand the fuzziness of this definition. Your argument stems from a fundamental misunderstanding of this idea.
By the way, the example above is not merely hypothetical, since species can be separated in space as well as time. We can observe this phenomenon in action through very fascinating phenomenon like "ring species".
https://en.m.wikipedia.org/wiki/Ring_species
Really cool stuff! I'd highly recommend learning about it.