The person giving the seminar was Doug Emlen, a biologist at the University of Montana. He has recently published a book called Animal Weapons: The Evolution of Battles, which looks at the evolution of large morphological weaponry in animals ranging from horns on small dung beetles to enormous antlers on huge elks. He discussed the conditions necessary for these types of weapons to develop, including environmental pressures such as intense competition, resources able to fight over and won, and one on one duels.
A discussion on this would have been great on its own, but he took it one step forward in an incredibly interesting direction. Dr. Emlen compared this animal arms race to the human arms race, finding some incredible similarities between the two. For example, he talked about a study done with caribou, where 11,000 confrontations were observed, and out of all of them, only 6 resulted in an all out battle between the two animals. These animal weapons are used as a deterrent, as male caribou "size up" other males in order to determine if a duel would be wise, and in most cases decide that it's not worth it. A comparison was then made to the Cold War, where the United States and USSR both had a huge amount of weaponry that acted as a deterrent, and in the end, no one officially declared war.
Below is an interview that was conducted on Scishow last month with Dr. Emlen that highlights the basic points of Monday's seminar (minus the comparison to the human arms race, unfortunately).