New evidence for why there are changes in mammals' spinal columns

May 21, 2019

A mammal’s posture while moving, or locomotor posture, plays a key role in how variable the number of vertebrae in its spinal column can be across all members of that species, a team of researchers, including Arizona State University graduate student Amy Peterson, has concluded in a new study appearing in the journal Nature Ecology and Evolution.

“While evolution has created change in many areas of an animal’s body,” said Peterson, an evolutionary anthropology student in the School of Human Evolution and Social Change, “there are some surprising consistencies among groups of animals, including how many vertebrae there are in the different segments of the spine."  Orangutan in tree Orangutans are "suspensory" mammals. Image credit: Wiki Commons Sandakan Sabah Sepilok Orangutan Rehabilitation Centre Download Full Image

Virtually all mammals have the same number of cervical (neck) vertebrae. Most also have between 19 and 20 combined thoracic (upper- and mid-back, with ribs attached) and lumbar (lower back) vertebrae. But, there are some species that show high variation between individuals in how many thoracic and lumbar vertebrae they have. For the species that show less variation, there must be a functional benefit to maintaining that stable number of vertebrae. Natural selection is working to keep that number stable because changing it is detrimental to the animal’s ability to move efficiently.

When a trait like number of vertebrae stays constant, despite many changes in how animals are moving, it means that there’s a reason that evolution cannot change that trait. For the cervical spine, it is thought that genetic mutations that affect the number of cervical vertebrae are also closely related to fetal abnormalities and defects. But this is not true of the thoracic or lumbar vertebrae, which means that their variation — or lack thereof — is controlled by how efficient it might be to produce variation in the spine.

Earlier research has suggested that the relationship between locomotion and stability in the number of vertebrae was primarily associated with running speed. Faster movement was thought to produce an evolutionary constraint on how many vertebrae could exist in the spine, while slower movement did not restrict variation in the same way.

This study, which included nearly 300 species of mammals from a wide variety of habitats, did not find evidence that slow-running species had more variation in number of vertebrae than closely-related, fast-running species.

Spinal column

The spinal column. Image credit: Wiki commons

To understand what factors might influence spinal variation, researchers conducted a series of analyses factoring in things like body posture; locomotor category; environment and habitat, such as arboreal or ground-dwelling; and locomotor speed. They found that suspensory mammals, like apes and sloths, exhibit the greatest degrees of variation in their thoracic and lumbar vertebral counts.

Suspensory behavior is a departure from the ancestral way of moving for mammals, which was to walk on all four limbs on the ground. Most terrestrial mammals have stayed walking on the ground, though some have adopted new behaviors, like the suspensory mammals. 

Running is not the only factor in how mobile or stiff an animal’s spine needs to be. Some groups, like bovids (cows and their relatives) and elephants, have stiffer backs among their largest members, showing that body size plays a role in spinal function. In primates, those adapted to suspensory locomotion — hanging down below branches in trees — have also developed stiffer lower spines in order to reduce the risk of buckling during suspension, which could damage the intervertebral disks and other soft tissue. 

Animals that have kept the ancestral body plan and way of moving, like dogs and horses, need to maintain the same number of vertebrae because their way of moving is most efficient with that number and altering that formula could cause them to be less efficient while walking and running. For animals that do not rely on the ancestral way of walking, such as suspensory groups, more variation can happen because it won’t affect their efficiency while moving around.

“It is clear that the changes in vertebral count across mammals have a complex evolutionary history,” Peterson said. “This new research highlights this complexity and is a step towards understanding how this trait has changed through time and across all mammal groups.”

Julie Russ

Assistant director, Institute of Human Origins


Psychology student wins Smith Marshall Scholarship, will study racial and ethnic health disparities

May 21, 2019

Xochitl Arlene Smola, a first-generation college student in Arizona State University’s Department of Psychology, was recently awarded the Smith Marshall Scholarship.

The Smith Marshall Scholarship is an endowed scholarship awarded each year to psychology students who have graduated from a high school in the state of Arizona and have excelled in their academic pursuits. Xochitl Smola, ASU Psychology Student Xochitl Arlene Smola is a first-generation college student in the Arizona State University Department of Psychology, and she just won the Smith Marshall Scholarship. Download Full Image

Smola’s early desire to understand the brain and behavior led her to explore the field of psychology, resulting in a passion for learning and research.

“The first time I heard the term psychology, it was as if I had cracked open a large book with light beaming out of it,” Smola said.

Because she is particularly interested in adolescent development, Smola has spent her time at ASU working with leading researchers including Nancy Gonzales, Foundation Professor of psychology and dean of natural sciences, and Leah Doane, associate professor of psychology and developmental area head. With Gonzales and Doane, Smola is working on ways to mitigate the racial and ethnic disparities that affect many Arizonan students. She credits Gonzales and Doane as two of the most influential mentors she has had at ASU.

As a first semester freshman, Smola became a research assistant at Bridges within the Culture and Prevention Research Lab, led by Gonzales. Bridges is a family-oriented intervention for middle school students and their families. The program works to reduce alcohol, behavioral and emotional problems in the long term by increasing engagement and support among families and within the school community. Smola has since presented research at a national conference and is currently working on her honors thesis with the lab.

Smola is also a research assistant at Transiciones within the Adolescent Stress and Emotion Lab, which is led by Doane. The Transiciones Project studies how the transition to college at ASU affects the physical and mental health of Latino high school students and their families. The lab uses physiological measures, such as hormone levels and sleep quality, to understand the impact of day-to-day experiences on physical and mental health.

Related: Mike Sladek Wins APA Dissertation Award on Transiciones Project

Smola’s work as part of the Bridges and Transiciones programs led to her “aha” moment: She realized she was captivated by the questions, experimental design and analytical aspects of psychology. She wanted to pursue a PhD.

“Working on these projects gave me the confidence to be where I am,” she said. “They have dynamically changed my career interests.”  

She hopes to one day become a researcher in the field of developmental psychology and to educate others on the challenges that ethnic students face in and out of the classroom.

“A lot of other ethnically diverse or first-generation students don’t have the opportunities I have had at ASU, so I think a lot of initiatives should go to answering these kinds of disparities, as well as health disparities,” Smola said. “Being awarded the Smith Marshall Scholarship is another great opportunity that will help me continue my academic studies.”

Smola said that as a first-generation college student and Hispanic woman, the Smith Marshall Scholarship has given her the confidence to ask questions and pursue a prominent career in research and developmental psychology. She encourages others to ask questions when they need it most.

“A big revelation I had while at ASU is that professors, faculty and peers want to help you succeed — the first step is to just be inquisitive and ask,” Smola said.

Smola has taken her love of learning one step further to the psychology department’s new Student Success Center, where she and others coach and tutor underclassmen.

“The really interesting and unique thing about the success center is that it’s specifically geared toward psychology. It is different from other tutoring centers because we’ve taken these courses, we’ve been in their shoes,” Smola said.

The goal of the center is to prepare undergraduate psychology students for success in academics and well beyond.

“As part of the inaugural SSC coaching team, Arlene has been instrumental in setting up the center and its initial success. Her enthusiasm is infectious to both the students and the other coaches,” said Whitney Hansen, senior lecturer in the Department of Psychology and supervisor of the Student Success Center. “She has used her advanced knowledge of statistics to help coaches review and students master the material. She is smart, passionate and supportive, which is why students who come to see her in the SCC keep coming back to receive coaching!”

Robert Ewing

Marketing and Communications Manager, Department of Psychology