This argument however is problematic since (1) is working with an understanding of species that is different from what modern biologists are working with.
The argument is only 'problematic' if one has already philosophically embedded oneself with one theory over another, and are closed to alternatives. And the operative word here is 'theory'
Also, the definition of species has changed over time and will likely continue to do so. It is a conveniently flexible idea that is often directionally bent to support a particular ideology.
In reality, observed nature proves Fr R's contention.
Father and many argues are using this kind of argument against evolution:
1) If parents always give rise to offspring of the same species, it follows that no new species can ever arise from preexisting life
2) Evolutionary theory states that new species do arise from preexisting life.
3) Therefore, evolutionary theory entails parents do not always give rise to offspring of the same species
4) But a cause cannot give what it does not have to give, therefore it is impossible that parents give rise to offspring of a different species.
5) Consequently evolution is false
I think it is helpful if we disambiguate between two uses of the term "species" since there is equivocation going on. For this argument to work, the use of "species" in (1), (2), and (4) has to be the same. So regardless of which definition you think is "right," or even which is accepted in science, the important point is that the understanding must be
consistent throughout the argument otherwise its an equivocation.
Here is the problem: suppose Father is working with an outmoded (according to modern biology) definition of species but that he thinks it has philosophical support. Fine. Call it "species*." Now, on this definition species are like equivalence classes so (1) is true. And let's concede Father Ripperger is correct about (4) as well on philosophical grounds. The problem is that the following is (2) is not true using species*. Evolutionary theory
does not claim that "new
species* do arise from preexisting life." Rather, proponents of evolutionary theory are working with a different understanding of species, call it species**. And while "new
species** do arise from preexisting life" is true, it is an equivocation to say that species* = species**.
But now, suppose critics of evolution decide to use species** as their working definition. But if that is the case, then (1) is false. Since species** does not treat species like equivalence classes, it is entirely possible that the antecedent of (1) is true but its consequent is false.
Do you see the problem here?