A duck walks into a bar, orders a drink and says "Put it on my bill."
Does that joke inspire you to read the rest of this post? I didn't think so. That is usually how people feel when speakers tell a joke or present "funny" slides during a talk. For some reason, many people have been told that they should try to win over their audience at the beginning of a presentation by telling a joke or funny story. You can hear politicians doing this all the time. How funny are they?
The point of this principle is that most people can't pull this off (like most politicians) and, more importantly, you don't need to win over your audience at the beginning with a joke. They are on your side from the very beginning. You don't have to win them over with humor. You won them over as soon as they walked in the door. They took time out of their busy day, or they traveled from a distant location, to hear your talk. Your job is simply to present your work in an engaging, honest, and concise manner.
The problem with forced attempts at humor is that you have lost track of why the audience came to hear you in the first place. They didn't come to a comedy club. They didn't come to a hear a TED talk. They came to hear about your science.
A second problem with telling jokes during science talks, which are inherently international, is that understanding jokes often requires fluency in the native language and deep familiarity with cultural norms. Thus, even a joke well told will tend to leave the non-native listeners cold. Or, worse, they will think your joke was part of the science and they will puzzle over how to incorporate your unusual words into the flow of the science that they came to learn about.
At the beginning of my thesis defense, I made the mistake of telling a joke. It wasn't the end of the world. But the joke bought me nothing. The audience was there to hear bout my work, not to hear my lame attempt at humor. These days, I find that the audience often laughs at one or more points during my talks. We are having a "conversation" about my science and sometimes humor sneaks in. I never plan these humorous moments, they arise naturally in the moment. Some speakers do, obviously, plan humorous moments and this can work, especially if it is well practiced. But it is certainly not necessary and those new to giving science talks should not feel like they need to tell jokes or be funny to give a successful talk. In most cases, it will detract from the talk.
Leave the jokes to the masters. They find it hard enough to make an audience laugh. You have a much easier job. You have data and your audience is hungry for data. Feed them data and everyone will be happy.