It’s what they don’t do that matters. They don’t disappear, leaving a fatal gap.
In “Why do organisms build tissues they seemingly never use?” (Michigan State University, August 10, 2012), Jeff Clune discusses the question:
Why humans and other organisms retain seemingly unnecessary stages in their development has been debated between biologists since 1866. This study explains that organisms jump through these extra hoops to avoid disrupting a developmental process that works. Clune’s team called this concept the “developmental disruption force.” But Clune says it also could be described as “if the shoe fits, don’t change a thing.”
“In a developing embryo, each new structure is built in a delicate environment that consists of everything that has already developed,” said Clune, who is now a postdoctoral fellow at Cornell University. “Mutations that alter that environment, such as by eliminating a structure, can thus disrupt later stages of development. Even if a structure is not actually used, it may set the stage for other functional tissues to grow properly.”
An interesting consequence is that newly evolved traits tend to get added at the end of development, because there is less risk of disrupting anything important. That, in turn, means that there is a similarity between the order things evolve and the order they develop.
The original story is kind of confusing, but it certainly sounds like design, not that they are allowed to say that, let alone believe it – the latter is a far worse offense.
The analogy offered, to a skyscraper replacing a roller coaster, is ridiculous because there is no functional or structural unity between the two artifacts. The situation is more like men having nipples because women need them. Embryo development that excluded nipples from the male, with no real benefit, would probably just not make sense.
Here’s the paper.