Dr. Jordan Okie, Arizona State University – The Evolution of Size

Sep 18, 2013

In today’s Academic Minute, Dr. Jordan Okie of Arizona State University explains why some species have evolved tremendous size.

Jordan Okie is a postdoctoral fellow at NASA’s Astrobiology Institute and the School of Earth and Space Exploration at Arizona State University. His work examines the effects of the size, metabolism, and temperature of biological systems on the properties of these systems and the implications of these effects for understanding ecology and evolution. He earned his Ph.D. at the University of New Mexico.

About Dr. Okie

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Dr. Jordan Okie – The Evolution of Size

The diversity of life is largely a matter of body size, which can vary by over 24 orders of magnitude in mass. To put this in perspective, the Earth is almost 23 orders of magnitude larger than an adult human. My research seeks to understand the underlying laws that govern the evolution and ecology of this diversity. Specifically, what factors influence the rate of evolution of body size, and what influences the maximum body size evolved by a lineage?

In collaboration with several other scientists, I developed new quantitative theory to provide some answers to these questions. The theory is developed from the observation that some organisms “live fast and die young”, while others take their time and mature much more slowly. Since larger organisms tend to live longer than smaller organisms, much of the diversity of among species can be attributed to body size. But we show that once these effects are accounted for, important residual variation remains,  which we call the slow-fast lifestyle continuum. The variation along this continuum reflects differences in the lifestyles and ecological niches of species. The theory demonstrates that lineages at the fast-end of this continuum can more quickly evolve larger sizes and can evolve larger maximum sizes than lineages at the slow end.

Our theory was well supported by data culled from fossil records of mammals over the last 70 million years. The groups of mammals at the fast-end of the lifestyle continuum, such as whales, evolved larger maximum body sizes and they evolved these maximum sizes more quickly than groups at the slow end, such as primates. By uncovering a new law of nature, this works provides insight into patterns of recovery from mass extinction events and the potential for modern species to adapt to climate change.

Production support for the Academic Minute comes from Newman’s Own, giving all profits to charity and pursuing the common good for over 30 years, and from Mount Holyoke College.