In the reading passage, there is ample support for the author's claim that the function of the appendage has been determined. It declares that the function of antlers of deer is totally clear. However, the professor in the lecture gives several reasons as a rebuttal to the author's point.
First, the professor in the lecture contends that antlers do not use as sexually attractive. Some of the male deer use this method to attract female deer. But it is not a key factor. Typically, they use other methods to breed their children, for example, vocalization and body shape. Also, males with small antlers are even able to get female deer. This casts doubt on the reading passage's claim that the appendage uses to attract male and the larger antlers the more preference.
Next, the professor in the lecture insists that deer do not use antlers to mark their territories. Most of them use scent, not rubbing antlers on trees. On top of that, the rubbing mark puts them in danger because it shows them where they are. Plus, the mark is not warning. This counters the reading passage's assertion that deer makes visual marks as a warning.
Finally, the professor in the lecture argues that antlers are not the method to defend themselves from predators. If it is the right way to use their antlers, they must need antlers in winter, the most dangerous season. Unfortunately, they shed their antlers in winter. Probably, they use antlers as protect themselves, not a major key.