Hi. I am Jon Fjeldså, professor at the biodiversity section of the Natural History Museum of Denmark, and I'm co-PI of the Center for Macroecology, Evolution and Climate, which is a research program funded by the Danish National Research Foundation. And I'm now seated in a replica of Charles Darwin's office placed in this museum. Today, more than 3 billion years after the origin of life, the global biodiversity has reached exceeding complexity. Biodiversity comprises everything from microorganisms to elephants, linked together in food webs or interacting networks of producers, consumers, and decomposers, competitors, and hosts of pathogens and parasites that make up the biological community on land, as well as in the oceans. The biodiversity represent our life support system. And therefore, if we want to manage the living resources and the world's ecosystem in a sustainable way, we also need insight into how it all works. This is done in the research field of ecology, which emerged as a distinct discipline at the turn of the 20th century. It gained prominence from the 1960s due to widespread concerns then about the state of the environment. These concerns are no less serious today. Initially ecologists worked on small scales with what was feasible at that time. Namely, studies of particular species and interactions between them and within a local environment. Gradually, the limits of what was possible at this scope broadened. 25 years ago, Jim Brown at University of New Mexico, Albuquerque with the introduction of the term macroecology started a new trend where ecologists move on to analyze general or global-scale patterns. The aim was now to develop predictive theories that could work on any spatial scale. So to say "laws of nature", applied to the living world. Because of the complexity of the living world, it is maybe optimistic to think that we can ever reach similar universal laws as what is possible in physics and mathematics, but at least we try to work towards the kind of understanding of basic principles and a unifying theory for what determines the complexity and distribution of life on Earth. The work towards this deep understanding has become possible now thanks to the computer technology that allows us to handle the enormous amounts of data that previously were scattered in publications, museum collections and in the heads of experts. Several research groups and the Global Biodiversity Information Facility have made an enormous effort in compiling these data in formats that can be combined with data from molecular systematics and analyzed in relation to the vast amounts of environmental data that are now available from satellite imagery and climate models. Already the first biologist explorers, who traveled around the world more than three centuries ago were amazed to experience the amount of variation in biological diversity around the world, and above all, they were amazed over the spectacular diversity in the humid tropics of the rainforest. They speculated over why biodiversity changed as one moved from the equator towards the poles, or from lowlands up to the mountane cloud forest and all the way up to the barren mountain tops. But they also observed great variation and exceptions to the general patterns which made it hard to come up with a unifying theory to explain the variation. Until today, more than one hundred different hypotheses have been proposed to explain this variation. Obviously, the variation must in some way be linked to the amount of energy received from the sun and thus temperature, combined with availability of water, but precisely how this happened was not quite clear. Early was assumed that diversity of species had to do with ecology, as more species would require higher productivity to maintain viable populations and thus higher primary productivity mainly through photosynthesis. This, in turn, requires energy from the sun and water, which would give higher rates of metabolism near the equator. And it was also assumed that, ecological dynamics and evolutionary rates would play a role. Complexity also had to play a role, first of all, because the amount of sunlight would vary with season and latitude, and precipitation and temperature could vary in quite complex and stochastic ways with certain areas being inherently very unstable. The macroecologists tend to believe that the variation must be rooted in laws of physics, energy, productivity, metabolic theory, and kinetics combined with segregation of species in different niches, and they try to use first principles of research to sort out these mechanisms. Relationships with the physical world was, first of all, studied by a correlative analysis, and assuming that the variation in biodiversity was everywhere at any time in equilibrium with the physical conditions. This, of course, is not the case because there is also history behind it. Biodiversity studies became a question of counting the number of species per area unit and correlating with physical parameters obtained from the numerous amounts of Earth data, remote sensing data, environmental models of various kinds and building of complex climate models to take into account all possible modifications. Assuming that a latitudinal diversity gradient is linked to a relationship between Earth and the sun and the variation in solar energy input, we must also assume that biodiversity gradient is as ancient as the origin of life. Still this does not explain how the gradient is generated over time. Whether it all originated in the tropics and dispersed towards the poles, or if new species could be generated anywhere, and in the end, vanished where conditions are very harsh and unpredictable, and therefore, accumulated where it was constantly warm. And we need to explore the whole range of such possibilities. In order to explore the range of possibility, we need to link present data versus a pattern to the past. During much of Earth's history, at least the most recent 200 million years, the entire global climate was warm (notwithstanding winter darkness in the polar regions). From this time on, there are fossils of palms and cycads even in the Arctic. So we may wonder whether the present-day tropical diversity was generated in the present-day rainforests, or if it was all over, and later was pushed towards the equator because of the global cooling that took place since the mid-Miocene. So there are two alternative hypotheses: "Out of the tropics" and "into the tropics". According to the first, life essentially evolved and diversified because of high energy and metabolism in warm and humid environments, and some evolutionary lineages later specialized to tolerate cold, as this allowed them to utilize the energy that was uncontested in the more harsh environments. According to the latter hypothesis, the organisms evolved anywhere and but often vanished except for those who reached the tropical rainforest, where stable conditions allowed them to persist, thus allowing a long-term accumulation of more and more species. The rhinoceros here actually belongs in a group that was widespread in Europe and Asia in the distant past. Today, after a series of big climatic perturbations during the Pleistocene period, they exist only in tropical Africa and southeast Asia. Thus, Earth history and population movement may be part of the mechanisms underlying the present day distributions. I will now describe a variety of mechanisms that may have contributed to the immense variation in biodiversity, not only the general trend, such as latitudinal trend, but also the strong degree of patchiness.