Theoretical biologist here. I haven’t looked this person up, but from the talk I’m going to assume he’s teaching an astronomy-related course. He does mention biology but I might be able to go into more detail.
I am also very skeptical about intelligent life existing in the universe. I’m certainly not saying it’s been proven false - of course it hasn’t - but from some of these responses I can’t tell if anyone has actually watched the video. I ran through it at 2x speed - it’s not technical at all - and I highly suggest watching it like that if you’re feeling like the title misrepresents factual observations. I’m not going to address the questions about astronomy, because I think the lecture covers those adequately.
First, let me say that I think it is entirely plausible that something that we could in theory come to recognize as life exists elsewhere. Please note that I am choosing my words very carefully. There is a discipline called exobiology that tries to understand what life actually is, what chemistries are compatible with the complexities we associate with living processes, and how evolutionary dynamics might affect them over time. We think that there needs to be an informational aspect as well as a physical-physiological aspect. The former provides the basis for replication and evolution, while the latter maintains integrity and what Schrödinger called “negative entropy” associated with living systems. It doesn’t have to be DNA, it doesn’t have to be in chromosomes. It will probably have to have something like a cell. It will probably need water. Other than that, I think I’m pretty open to ideas.
Complex life, and in particular life exhibiting technological intelligence (which is how most of us think of intelligent life) is a much higher hurdle. Earth - our single example - has been fairly teeming with life for around 3.5 billion years, give or take. It is evolutionarily highly dynamic (for whatever that means when your sample size is 1) with both mutation and recombination playing roles in genetic and phenotypic diversity. The sheer diversity of factors - transcription, regulation, editing, and so on all provide targets for evolution. Complexity builds upon complexity.
And, given all of that, there has been exactly one single line that has led to technological intelligence. It evolved once. And the thing of it is that, evolutionarily, it’s a really good idea - so much as to allow humans to drive themselves and wide swaths of the entire global ecosystem to the border of extinction. When good ideas occur, they tend to evolve early and often. Eyes are a great example. It’s a very good idea to be able to perceive light, and at my last count I believe eyes have evolved independently around 24 times.
If intelligence evolved once - and we’re not talking about dolphins or dogs here - despite the fact that it allowed humans to almost instantly become the apex species on the planet - that tells us it’s very hard to discover from an evolutionary point of view.
Long story (not so) short, I think it’s unlikely that humans will ever encounter an extraterrestrial technological intelligence. I think that, if we should survive the next century or two, we could likely find the equivalent of bacterial mats. This would be hugely exciting for biologists and would (in a very very literal sense) change life as we know it. We’re just not going to find big headed bug eyed aliens in flying saucers or Vulcans.