Smelling to Survive: Chemical Ecologist Sniffs Out How the ‘Smellscape’ Impacts Life on Earth

April 3, 2024
Prof. Dr. Hansson speaks behind a podium. An image of a woman and baby are projected on the screen to his right.

Sometimes considered “primitive”, our sense of smell is vital to how humans and other living creatures interact with each other and their environment. Organisms use smell to locate food, find mates and avoid dangers, yet human activities are changing the global smellscape upon which much of life relies.

Esteemed scientist Professor Dr. Bill Hansson, Director and Scientific Member at the Max Planck Institute for Chemical Ecology in Germany shared his work in understanding olfactory science with a crowd of nearly 500 at the final Science Meets Music event of 2024 on March 27.

In his lecture, “Smelling to Survive,” Professor Hansson discussed the versatility and importance of smell to humans and other organisms, different animals’ olfactory adaptations, as well as his research into how human activities are changing insects’ ability to carry out important activities like feeding and mating.

How Olfactory Receptors Help Living Things Navigate the World

Dr. Hansson explained that the human eye contains receptors for three colors. With red, blue and green the human eye can understand a vast ocean of visual inputs.

The nose, on the other hand, contains 400 unique receptors, each of which respond to unique molecules in the air to stimulate the brain’s olfactory bulb. These receptors work together to identify millions of odors, perhaps even more.

An apple contains 300-400 types of molecules related to odor, Dr. Hansson explained. The human nose detects the 10-20 molecules that are necessary to recognize the smell of an apple and distinguish Granny Smith from Cortland.

These receptors help humans navigate the world around us. They influence our ability to taste (which is mostly smelling, through a process called retronasal smelling). They enable us pick up on pheromones to identify people close to us like children and mates, and even to follow a trail.

“Many who got COVID lost their sense of smell,” Dr. Hansson recalled. “When you lose something, you really know what it’s worth.”

Yet humans have a small number of smell receptors compared to some other mammals:

  • Dogs: With a nose 1,000 times more sensitive than a human’s, a dog can smell something 10 meters underwater. Dogs can identify cancer in humans by smell and pick out trees infested with insects.
  • Mice: Totally dependent upon smell, a mouse has four noses that help it find a mate, locate food, and avoid predators.
  • Fish: Salmon find their way upstream to spawn by smelling the creeks and rivers where they were born. Baleen whales have a keen sense of smell to help them sniff out plankton in the vast ocean.
  • Birds: With huge olfactory centers, many birds have an excellent sense of smell. Turkey vultures and albatrosses smell for their food, and penguins use odors to assist in mating behaviors.
  • Insects: Even bugs rely on smell. For instance, bark beetles produce a pheromone to signal other bark beetles to feast on a tree. When they tree is full of beetles, they switch to a scent that tells others to find a new place to dine. Some moths have very finely tuned receptors that can detect miniscule concentrations of sex pheromones in the atmosphere.
  • Plants: Plants can smell too, Hansson explained. Corn, for instance, will change its odor when attacked by insects to warn other corn to activate its defenses.

With a world so dependent on smell, Hansson’s research has focused on how humans are impacting our environment.

Investigating the Changing Smellscape

Unfortunately, human manufacturing and pollution is changing the landscape of smell for insects and other animals. Greenhouse gasses such as ozone, nitrogen oxides, and carbon dioxide emitted by human activity can degrade pheromones sent between insects. That’s because many pheromones have double bonds that are sensitive to ozone and can easily break apart, negatively impacting the insects’ ability to communicate.

His research examined the connection between the tobacco flower and the tobacco hornworm, which is the moth that pollinates it. Thanks to its keen sense of smell, the moth can locate the flower even in total darkness. Yet after exposing the flower to high levels of ozone, the moth was unable to find its target.

“Moths are extremely important pollinators,” he explained. “Many of the things we eat would not grow without these pollinators.”

Similarly, Hansson’s lab demonstrated that male fruit flies exposed to ozone lose the ability to distinguish male from female flies, resulting in males courting each other. The ozone gasses break down the flies’ olfactory communication system, Hansson explained, so they can’t identify prospective mates.

“The sense of smell is versatile,” said Prof. Dr. Hansson, “whether it’s your own body, in your dog you associate with so closely at home, and other organisms that might be further away from you, the sense of smell is important for all.”

The evening also featured a performance by The Chamber Music Society of Palm Beach (CMSPB). Musicians included Arnaud Sussman, violin, Nicholas Canellakis, cello, and Michael Stephen Brown, piano. CMSPB has brought extraordinary chamber music performances and educational programming to Palm Beach County and the wider South Florida region since 2013.

About Dr. Hansson

Prof. Dr. Bill S. Hansson is a Director and Scientific Member at the Max Planck Institute for Chemical Ecology. From 2014-2020, he also served as Vice President of the Biomedical Section of the Max Planck Society, where he provided leadership to the 27 Max Planck institutes in Germany and the Max Planck Florida Institute for Neuroscience in the USA. He also coordinated the international work of the MPS with partner organizations in Shanghai and Buenos Aires and 19 Max Planck centers all over the world.

For media inquiries, email Katie Edwards.

Science Meets Music is generously sponsored by the Honorable David Fischer & Mrs. Jennifer Fischer. 

ABOUT MAX PLANCK INSTITUTE FOR NEUROSCIENCE

Max Planck Florida Institute for Neuroscience (MPFI), a not-for-profit research organization, is part of the world-renowned Max Planck Society, Germany’s most successful research organization with over 80 institutes worldwide. Since its establishment, 30 Nobel laureates have emerged from the ranks of its scientists. As its first U.S. institution, MPFI provides exceptional neuroscientists from around the world with the resources and technology to answer fundamental questions about brain development and function. MPFI researchers employ a curiosity-driven approach to science to develop innovative technologies that make groundbreaking scientific discoveries possible.

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