In 1932, biologist Max Kleiber observed that as organisms get bigger, their energy needs increase. But this relationship isn’t linear: larger lifeforms use less than proportionally more energy. Known as Kleiber’s law, this is one of the essential rules in biological scaling. Such relationships allow scientists to study how natural phenomena vary from small to large scales. In 2000, the Santa Fe Institute published “Scaling in Biology,” a seminal book that crystallized the field’s collective knowledge.
Since then, a lot has unfolded in this area of biology. “There have been some major theoretical advances that allow us to have more precise theories that predict a greater number of things in terms of scaling relationships,” says SFI Professor Chris Kempes. “The field has expanded the scope from the original focus on mammals and vascular plants to everything from unicellular bacteria to viruses.” November 15–17, SFI External Professors Brian Enquist (University of Arizona), Mary O’Connor (University of British Columbia), and Kempes led a workshop called “Synthesizing Biological Scaling: Towards a Universal Theory” to take stock.
At the event, international experts on scaling delivered talks and debate hot topics during breakout sessions. “The hope is that it will help resolve some long-standing conflicts in the field or help people understand how some of those conflicts were recently resolved,” says Kempes.
For example, several presentations will address concerns around the network model, which states that evolution influences scaling relationships in the biological world. “Natural selection has maximized resource extraction and distribution within the body,” Enquist explains. Take the case of the vascular network. “There’s a maximization of the network that it tries to supply the entire body, but at the same time, the network is also minimizing transportation times and the work involved in distributing the resources,” says Enquist. However, he says, it’s unclear if the hypothesis holds in unique organisms like bacteria that don’t have well-defined transportation networks. The workshop is also crucial because SFI plans to publish a follow-up edition of “Scaling in Biology.” “Everyone’s coming to this meeting with an understanding that we are going to write a second book,” says Kempes.
Speakers, who are all potential contributors, summarized their chapters through the presentations. Enquist was one of the original book’s contributors and a former Postdoctoral Fellow at SFI. “I never in my wildest dreams thought that I would be coming back to SFI a little over 20 years later to extend the scope — and assess the implications — of these same questions,” he says. The field now includes questions about the role of temperature and climate in biological scaling, and researchers use scaling approaches to predict ecosystem functioning and the future of the biosphere in a changing climate. “These questions and challenges have brought whole new dimensions to the original scaling work developed at SFI,” says Enquist.
The workshop and subsequent book will address how close the scientific community is to formulating a universal theory of biological scaling. “Universal theories are nice,” says Kempes, “because they make the world simpler for us.” For example, a universal theory
of biological scaling would allow scientists to build simpler models of the biosphere, and that’s important to address some of the pressing problems our planet faces. “Universal theories come with more predictive power, and we may need that for forecasting future ecology under climate change,” says Kempes.