Darwin’s first point is about sterility. Crossing two species can often create an offspring, but that offspring will more than likely be sterile and unable to reproduce. The next point he makes is that we shouldn’t expect to find intermediate species (links between two species) because evolution is a relatively slow process. One species doesn’t become another within a generation. Changes take many years to happen enough to warrant something being considered a new species. Another argument is the existence of selective breeding. Just since humans began roaming the planet, enormous amounts of plants and animals have changed and many of those changes are to our benefit. We have forced evolution to make our lives easier. The last point I’ll list is how similar creatures of the same climate are. Many animals and plants adapt to their location in the same way.
I hope that I’m not the only one, but I found Darwin to be incredibly difficult to understand. He sometimes seemed like he was saying one thing and then a moment later he was claiming the exact opposite of it. Regardless, I found many things he said to be very convincing. Most convincing to me is the changes that humans have made to plants and animals in our time. We truly appear to have evolved things like dogs and corn to our benefit and I don’t think these things would have happened without human presence. The least convincing argument to me is that about sterility, fertility, and vigor. From what I gathered, Darwin claims that crossing two species creates something that is similar to its parents, but stronger and incapable of breeding. I would need more evidence of this than he provided, but I also recognize that I may have misunderstood him entirely.