Spotlight on Simmons

Professor Aids Discovery on Animal Evolution

"Tree of Life" Uprooted: Q&A with Simmons College Professor Akiko Okusu

Assistant Professor of Biology Akiko Okusu is part of an international research team that published a study in the April issue of "Nature" magazine about a new tool for genomics (the study of gene sequences in living organisms) used to reveal new findings on animal evolution. The study, led by Brown University, involves 40 million base pairs of new DNA data taken from 77 animal species. The findings include some surprises, as Okusu discusses below.

What discoveries did your "tree of life" study find, and why are they so important for scientists - and for the rest of us?

Akiko Okusu: Our study makes surprising discoveries that dispute long-held views on animal origin and evolution. One of the most striking findings is the position of sponges on the evolutionary tree. Sponges are motionless, brainless bags of cells that lack a mouth, an anus, or a gut. They have been considered to be the oldest known animals found on earth, with fossil evidence supporting their existence for at least 543 million years.

Our findings, however, suggest that some of the more complex animals, comb jellies, are the oldest animals. Comb jellies have a complete digestive system and can move freely using their developed muscles and nervous system. It seems that the ancestor of all animals was not as simple or primitive as we originally thought.

But why are the roles of these little creatures in the evolutionary chain such a big deal?

Okusu: If our hypothesis holds true, our previous notion about the primitive state of the digestive, muscle, and nervous system among animals is completely overturned. Simple does not necessarily equal primitive, and having complex structures does not necessarily equal being advanced, better, or intelligent. We definitely will be teaching biology very differently.

Why should we, in today's society, care about the evolution of species that happened millions of years ago?

Okusu: A "tree of life" — the concept that all living organisms diverged from a single common ancestor — provides a framework to understanding many aspects of life. All living animals, from comb jellies to humans, share a common ancestor and therefore share a similar genetic toolbox. The human body is complicated and in many ways difficult to study. Looking for the common building blocks in simpler but related organisms enables us to understand aspects of our own body in a simpler state.

Evolutionary "tree thinking" helps us make significant scientific advancements. It has led to fundamental improvements in our understanding of issues such as the origin of viruses including HIV and SARS, and the origins of Homo sapiens and antibiotic resistance in bacteria, and even helped solve criminal forensic cases. Evolution is all around us!

What was your role in the study?

Okusu: My major role was to travel around the world collecting marine invertebrate species that may hold the key in resolving the animal tree of life. The project required many scientists with a wide array of expertise to study each of the organisms. I had the opportunity to travel with a "dream team" of specialists to Sweden, Australia, and Japan to collect the specimens, many of which are rare and quite difficult to find. In fact, prior to this study, genetic data had never been known for 11 of the 77 species collected.

I became involved in the project during my graduate and postdoctoral careers at Harvard University. I was chosen to help collect and study the molluscan group, especially shell-less molluscs called aplacophorans. There are probably only 10 scientists in the world that study aplacophorans, and I am one of them!

Our team has worked together now for five years. This is the first major publication that we produced together, and we are extremely happy about these initial results. There will be many more exciting new findings coming out of this "Assembling the Tree of Life" project, so stay tuned!