How could the authors suddenly do this? Some of the following points may be considered.
The public is being prepared very slowly for the demise of Darwinian evolutionary theory. It wasn’t planned this way, but it is how things are playing out.
The giraffe is one of those all-star icons of evolution, familiar from textbook covers, that falls apart on closer inspection.
Many high school students are eager to go beyond the brief and airbrushed presentation of evolutionary theory found in their biology textbooks, and are full of questions.