Study of Dogs’ and Wolves’ Sensitivity to the Scent of Human Fear

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The Ability to Detect the Scent of Fear

Dogs are capable of picking up scents associated with human fear. Until recently, it was unclear whether this ability developed during thousands of years of coexistence with humans or if it originated much earlier. To answer this question, researchers compared the reactions of dogs and wolves to the scent of sweat from people experiencing stress.

Hypotheses on the Origin of Sensitivity

There are two main hypotheses regarding the origin of this sensitivity. The first suggests that the ability to perceive human emotional signals emerged during domestication, when humans unintentionally selected animals that better understood their behavior. The second hypothesis claims that this ability already existed in the common ancestor of modern dogs and wolves and was preserved after the species diverged.

Experimental Approach

To test these hypotheses, scientists from the University of Veterinary Medicine in Vienna compared not domestic dogs with wild wolves, but with wolves raised by humans from an early age and accustomed to regular human contact. This approach minimized the influence of life experience: if differences between the species appeared, they could be attributed to domestication. If the reactions were the same, it would indicate an ancient origin of the ability.

The experiment involved 24 dogs of various breeds and 11 gray wolves, all raised by humans and given similar training. To obtain scent samples, 19 volunteers each provided sweat samples from their armpits twice: once in a neutral emotional state and once after completing a stressful task involving public speaking and solving arithmetic problems under observation. To confirm the volunteers’ stress, researchers measured their anxiety levels and physiological indicators.

Conducting the Experiment

The collected samples were placed in special containers, and the animals were then offered a choice between them. A familiar human experimenter, unaware of which scent was which, was present with the dog or wolf. Researchers recorded dozens of behavioral parameters: the time spent near each scent, the speed of choice, how often the animal looked at the human, exploration of the room, and instances of refusing to make a decision.

Results and Conclusions

The experiment showed that both dogs and wolves changed their behavior when exposed to the scent of fear. The animals did not show a clear preference for or avoidance of sweat samples from fearful people, but their overall behavior shifted: they paid more attention to the accompanying human, hesitated longer before making a choice, and more often refused to decide.

The only significant difference between the species was that dogs more frequently ended the test early and left the experimental area, while socialized wolves did not show this tendency. This may reflect differences in behavioral strategies that developed after domestication: dogs tend to avoid uncertain situations, while wolves continue to explore their surroundings.

The main conclusion of the study is that the qualitative reaction of dogs and wolves to the scent of fear was the same. This suggests that sensitivity to scent signals linked to human emotional states likely did not arise solely as a result of domestication. Most likely, this ability already existed in the common ancestor of modern dogs and wolves and has been retained in both species.

Study Limitations

The experiment involved not wild wolves, but wolves raised by humans from an early age and accustomed to close contact with people. Therefore, the results cannot be automatically applied to wild wolf populations. Additionally, the study did not determine exactly which chemical compounds in human sweat serve as signals for animals or how universal this reaction is.

Significance of the Results

Despite these limitations, the data obtained provide some of the strongest evidence that dogs’ ability to respond to the scent of human emotions may have much more ancient origins than previously thought. If these findings are confirmed, it would mean that the evolutionary prerequisites for close interaction between humans and dogs arose long before the process of domestication began.