When it comes to mammals, how big is too big?

June 13, 2013

Researchers explain maximum size in mammals

Mammals vary enormously in size, from weighing less than a penny to measuring more than three school buses in length. Some groups of mammals have become very large, such as elephants and whales, while others have always been small, like primates. A new theory developed by an interdisciplinary team, led by Jordan Okie of Arizona State University, provides an explanation for why and how certain groups of organisms are able to evolve gigantic sizes, whereas others are not. seals Download Full Image

The international research team comprised of palaeontologists, evolutionary biologists and ecologists examined information on how quickly an individual animal grows and used it to predict how large it may get over evolutionary time. Their research is published in the journal Proceedings of the Royal Society B.

The new theory developed from the observation that some animals live fast and die young, while others take their time and mature much later. This is called the slow-fast life-history continuum, where "fast" animals – such as mice – breed very quickly, while humans mature slowly and are relatively older when they first have children. The theory proposes that those species that are relatively faster are more likely to evolve a large size quicker than slow species, and that their maximum size will be greater.

The research team tested their theory using the fossil records of mammals over the last 70 million years, examining the maximum size of each mammal group throughout that time, including whales, elephants, rodents, seals and primates. They found that their theory was very well supported.

“Primates have evolved very slowly, and never got bigger than 1,000 pounds,” said Okie, an exploration postdoctoral fellow in the School of Earth and Space Exploration at ASU. “The opposite was true of whales, which evolved their large size at the fastest rates recorded.”

The theory also makes predictions about the relative risks of extinction for large animals compared to small. The maximum size of an animal is limited by the rate of mortality in the population. Because larger animals tend to breed less frequently than smaller animals, if the mortality rate doubles, the maximum size is predicted to be 16 times smaller.

“This is a really surprising finding,” said co-author Alistair Evans of Monash University (Melbourne, Australia). “It points to another reason why many of the large animals went extinct after the last Ice Age, and their high risk of extinction in modern environments.”

The research clarifies some of the differences among the main groups of mammals and makes further predictions about how changes in body size affect the evolutionary potential. In the future, this work will be extended to help explain how extinction risk may be reduced in changing climates.

The team was funded by a Research Coordination Grant from the US National Science Foundation. Financial support to Okie was provided by an Exploration Postdoctoral Fellowship from Arizona State University’s School of Earth and Space Exploration and a National Aeronautics and Space Administration Astrobiology Institute Postdoctoral Fellowship.

The School of Earth and Space Exploration is an academic unit of the College of Liberal Arts and Sciences.

Nikki Cassis

marketing and communications director, School of Earth and Space Exploration

Samantha Stachel 'Play Big' scholarship to benefit Barrett honors students

June 13, 2013

Samantha Stachel was the "Hannah Montana" girl who lived a double life – the average school girl by day and a determined, powerful and peaceful warrior by night. She played big her whole life regardless of the circumstances.

Although Stachel battled Ewing’s Sarcoma, a malignant bone tumor, she lived her life to the fullest. Cancer was seen as just an inconvenience. Surgery one day…the next day at her brother’s soccer game. Chemotherapy in the morning...back at school by 11:00 a.m. Samantha Stachel Download Full Image

Cancer has tried to knock me down with several recurrences since the age of seven, specifically three times during high school. Each and every time I pushed forward, refusing to quit or slow down,” Stachel wrote in her admissions essay for Barrett, the Honors College at Arizona State University.

Stachel highly valued education. She continued her essay by saying, “During this demanding time, I committed to maintaining as normal of a life as possible. With the support of my teachers and family, I strived to attend school on a regular basis, stay current with my assignments and prepare for tests. It was not easy but my determination produced rewarding results.”

Stachel was a committed student who earned a 4.0 GPA at Chaparral High School in Scottsdale. She was a member of the National Honors Society and also established a humanitarian club called Helping Hands where she enlisted the help of her classmates to participate in holiday gift drives, charity walks, fundraisers and hands-on service to benefit local non-profits and her annual adopt-a-family gift drive. The club’s motto is “Helping our community, one hand at a time.”  

Her stellar academic achievements and community service credentials led to her being admitted to ASU as a history major, and to Barrett, where she was very excited to attend this fall. She loved Barrett for its supportive community of students.

Stachel added in her admissions essay, “The obstacles of chemo treatments, multiple surgeries, radiation, weekly doctor visits, and monthly scans have challenged me every step of the way but also have strengthened my resolve, built my character in terms of my approach to my life, taught me compassion, and given me a deep sense of gratitude. My life experience has made me realize my desire of helping others. Being fortunate to have support during my journey to achieve my health goals, I, in turn, would love to help others achieve their goals.”

Stachel passed away on April 18, 2013 at the age of 18.

“Samantha gave and received love that can fill many meaningful lifetimes,” said Stachel's father, Paul. “She valued integrity, people, communication, humor and family. In every aspect of her life Samantha always played big.”

While Stachel cannot physically attend ASU as a student, her spirit and passion for helping others will be present at Barrett through the “Samantha Stachel 'Play Big' Scholarship” established in her honor. The scholarship will be awarded to students who demonstrate academic excellence, character and leadership in the face of challenging circumstances.

“Barrett is a place where Samantha planned to play big,” Stachel’s mother, Barrie, added. “This scholarship fund will allow her to do that through the dreams and accomplishments of others who overcome their own personal obstacles."

“The criteria for the scholarship recipients are simple,” Barrie continued. “They should be steadfastly committed to education and willing to leap over obstacles to achieve their goals. Maybe they’ve been bullied, faced a difficult living situation or had a health challenge. The common thread is that, like Samantha, they did not let their circumstances define them or their goals.”

The Stachel family has set a goal of raising $100,000 in the first year and growing the fund to $500,000 over successive years. In just the first month since the fund was established, more than $60,000 has already been contributed. Additional information about the scholarship, and how to contribute, is available at http://barretthonors.asu.edu/about/scholarships/samantha-stachel-play-bi....

“Samantha played big...that is her legacy. That’s why we came to Barrett to establish a scholarship in her name, because Barrett is a place where the students play big,” Paul said.

“We want to help people who are facing their own challenges and who will be inspired and go forward to accomplish great things. Samantha was a person who led by action and we want to support others to do the same,” he added.

“Every time I tell my story, I inspire others to face their challenges. Everyone has or will have challenges. The challenges may not be the same but knowing that others also have a story helps people to believe they can step up to their challenge. I learned to not only share who I truly am but to express myself because no matter what, I am loved. Taking this risk and choosing to walk through the public door helped me to share my story, set me free, and send me on my way to continue my life’s journey and hopefully inspire others to do the same.” – Samantha Stachel

Nicole Greason

Director of Marketing and Public Relations , Barrett, The Honors College