Exploring Evolution in Class 9

To enhance her students’ study of Biology, Upper School science teacher Iris Hood invited postdoctoral scholar Dr. Mirna Marinic to a recent 9th grade class to discuss her fascinating work in the field of evolutionary and developmental biology and to engage in an illuminating Q&A.

“This visit was part of a larger discussion about the evolution of sea to land and the first steps towards the evolution of four-legged animals, also known as tetrapods,” said Dr. Hood.

Prior to Dr. Marinic’s virtual visit, students watched “The Origin of Four-Legged Animals,” featuring Dr. Marinic’s colleague Dr. Neil Shubin, and a documentary called “What Darwin Never Knew.”

Dr. Hood noted, “These prior lessons served as the grounding concepts for students to take into our discussion with Dr. Marinic and inspired many of their questions about evolution.”

Dr. Marinic, originally from Croatia, received her PhD from Germany before coming to the United States. “My first job in the United States was studying the evolution of pregnancy in mammals,” she said. Her current job at the University of Chicago allows her to study the regeneration process of appendages in Axolotls, an animal in the amphibian family that have four legs, a long body and tail and feather-like gills around their heads.

“What’s your favorite part of research?” one Class 9 student asked to kick off the discussion.

“Developmental biology,” Dr. Marinic said, who sported a virtual background of a brown axolotl swimming through vibrant green plants. “It’s amazing to start with an embryo and watch it transform into a grownup. You can start with one cell and down the line you have a blue whale. What’s not to like?! How is it possible!”

One student mentioned hearing that axolotls are known as ‘Nature’s Miracle Healer’ and wondered if there was any truth to that.

“Yes! Not only are they animals that can regenerate, but they are top notch! They can do internal regeneration as well,” Dr. Marinic explained. “Many mammals can regenerate—it even happens in us, with our skin or line of our intestine—but axolotls can do this after injury.” Dr. Marinic noted that they even produce scar-free regeneration and it’s nearly impossible to tell if a limb was ever broken or detached.

Another student questioned, “Is there a limit to regeneration?” Dr. Marinic explained that the younger axolotls are able to go through the process faster and with ease. While the skill may diminish over time, they’ll never fully lose the ability.

Dr. Marinic also described a unique feature of axolotls: In addition to their gills, they also have lungs and can breathe out of water despite being aquatic animals. “They can swim just fine with two limbs amputated!”

Another student questioned the ethics of researching regeneration asking, “Doesn’t it hurt the animals?”

Dr. Marinic assured the students that the animals are nurtured and put to sleep using anesthetics to avoid any pain. “If they show any signs of discomfort, painkillers are administered. There are many laws in place for lab practices.” She explained that before beginning this kind of research, one must provide a detailed proposal to the Board describing why it is necessary and how you can reduce the number of animals used. “It’s a very regulated practice,” Dr. Marinic said.

“What if the nervous system is severed? Can they still grow back?” Dr. Marinic clarified that, unfortunately, regeneration won’t happen if the nervous system is severed, however, axolotls are very talented creatures and can sometimes grow an extra limb by reprogramming the nerve.

It was clear that this informative Q&A left students inspired with their minds churning and looking forward to their next Biology lesson.