How do organisms evolve in response to global change?

Welcome. My name's Bree Rosenblum. I'm a professor of global change biology at the University of California, Berkeley. Today, we're going to be talking together about how organisms evolve in response to global change.

I have three big goals for our time together. The first is that I really want you to understand, what is human-mediated global change? How is our planet changing, and how are humans responsible for a lot of those changes? The second is that I'd like you to understand how organisms evolve in response to those changes we're inducing on the planet. Humans are making changes, all of the other species are responding, and that interaction is really important for understanding evolution on our planet today. Third, I'd like you to understand why the field of evolutionary biology itself is so important in this day and age. How our field helps us understand, predict, and respond to changes that we're seeing on our planet.

Let's jump in. As an evolutionary biologist, it's really important, to me, to give a really quick big-picture context to the story we'll be telling today. We're going to take a very rapid journey through the history of life on our planet.

The story of life on Earth begins 14 billion years ago, which is when the story of everything in our universe begins. The Big Bang led not only to an incredible change, an incredible creation of an entire universe, but also led to the formation, ultimately, of hundreds of billions of planets in our own galaxy, and hundreds of billions of galaxies in the universe. We as humans on planet Earth are particularly interested, obviously, in our own planet, which has about a 4.5-billion-year history. Even though the earth formed this long ago, it took a long time before conditions on our planet were stable enough to host life. And it took a really long time until there were even any stirrings of the foundations of life on our planet. Well before there was cellular life, there were macromolecules. All life forms on planet Earth have DNA- or RNA-based genomes, and these macromolecules didn't appear on our planet until about 3.8 billion years ago. It took hundreds of millions of years after that for the first cellular life forms to begin, and almost another billion years until we had significant oxygen accumulation in the atmosphere. The first eukaryotes, the first cells that had nuclei, and the first stirrings of multicellular life where those cells began to live together took millions and millions of more years. And it's not until what we call the Cambrian explosion about 500 million years ago where we really see a modern world of what we consider to be the major lineages that we recognize today as animal life on this planet. Obviously, we have a phenomenal tree of life. Animals are only a teeny, teeny, teeny part of that. But in terms of bringing us up to the present moment and up to this moment where our species rose to dominance, this Cambrian explosion was a really important time. Nearly all the major groups of animals appeared within 10 million years. Over the course of the next tens of millions of years, many of those lineages diversified into what we recognize today. For example, mammals are about 100 million years old, and our own species is about 6 million years old, in terms of the divergence of Homo sapiens from our great ape common ancestors. Most people don't understand the complexity of our own history as humans. It's not just that we have a single human species on the planet now. It's that we have had a rich history where multiple different species of humans have evolved. Some of them have even co-occurred in space and time, and all of those millions of years of history have led to this moment where there is a single species of human on the planet. The changes that we've wrought on the planet are not only very modern. Some of them go back thousands of years. In fact, we started having regional impacts on the planet tens of thousands of years ago. As we started hunting, as we started cultivating, as we started domesticating crops and animals, we changed not only our societies, but we started to change the face of the planet. Over the course of the last tens of thousands of years, we have seen an absolute explosion in human population growth. We now have more than 8 billion people on the planet. Even though we were already having local and regional impacts tens of thousands of years ago, we are now having an unprecedented global impact on the planet. I'd like to really quickly walk you through some of those impacts. Often, this part of the talk feels a little bit depressing, like, wow, we've done all that in such a short amount of time. But I'd like you to stay with me and just look at the different categories of impacts we've had over the last several hundred years. One of the biggest ways we've literally changed