Emotions are complex psychological and biological states associated with moods, temperament, personality and disposition. They drive how we perceive and react to environmental stimuli. But not all animals experience emotions in the same complex way that humans do.
If you’re short on time, here’s a quick answer: Insects, spiders, fish, amphibians, reptiles and very simple marine invertebrates likely do not experience emotions as we typically understand them.
In this comprehensive article, we will analyze the latest scientific research on animal emotions and sentience to understand which creatures likely lack this mental capacity and why. We will explore what defines emotion, the evidence for sentience across species, and why certain types of animals may not have the biological hardware for emotional experiences.
Defining Emotion and Sentience in Animals
The Complex Biology Underpinning Feeling
Emotions and feelings in animals involve complex neurobiological processes. The limbic system, including the amygdala and hippocampus, along with cortical structures and neurotransmitters like dopamine and serotonin, form an interconnected network that generates emotional states.
More primitive areas like the periaqueductal gray also contribute to innate emotional reactions. So even without human-level cognition, animals can still have subjective experiences and feel sensations like fear, anxiety, and pleasure.
Key Structures for Emotional Processing
Research shows that mammals, birds, and possibly some other vertebrates share key brain structures involved in experiencing emotions. For example, the amygdala processes threats and rewards across many species.
And birds have a pallium region that may support emotional experiences similarly to the mammalian cortex. So while animal emotions may differ in complexity from humans, core feeling abilities likely evolved very early in vertebrates and persist across diverse modern species.
Indicators of Sentience
Scientists assess animal sentience – the capacity to have subjective experiences – through behavioral tests and neurological observations. For instance, learned helplessness experiments reveal that dogs, rats, and chickens can all exhibit depression-like states.
Brain scans also show reptiles, fish, and invertebrates like octopuses exhibiting emotional processing activity. So evidence points to a wide spectrum of animals perceiving sensations, having awareness, and feeling distressed or content depending on their circumstances.
Invertebrates and Fish May Not Feel Emotions
Insects Operate Mostly on Instinct
Insects like flies, ants, bees, and cockroaches have simple nervous systems and miniature brains that likely don’t have the capacity for emotions like mammals do. They operate mostly through instinct and reflexes, not subjective feelings.
For example, a fly doesn’t have the neurological ability to “feel” fear when you try to swat it. The fly simply detects a threat through sensory input and reacts by trying to escape.
Spiders Lack Complex Brains
Spiders and other arachnids have even simpler brains and nervous systems compared to insects. With a distributed network of ganglia rather than a central brain, spiders lack the neural complexity believed necessary for emotions like fear, joy or sadness.
While they can detect and respond to stimuli, spiders probably don’t subjectively “feel” anything akin to an emotional state.
The Question of Pain in Crustaceans
There is debate around whether some invertebrates like lobsters and crabs can feel pain. They certainly detect and respond to damaging stimuli, but some say they lack the neural capability for a subjective experience of suffering.
Recent research suggests crustaceans do show neural responses consistent with basic emotional states and feeling pain.
Do Fish Have Feelings?
The neurological capabilities of fish are more advanced than invertebrates but more basic than mammals and birds. Most fish have small brains relative to their body size compared to other vertebrates. However, some research suggests fish may have greater mental abilities than previously thought.
For example:
- Some fish recognize faces and can learn complex spatial relationships.
- Fish produce dopamine and opioids that may mediate emotional experiences like fear, stress or pleasure.
- Areas of the fish brain are analogous to parts of the human brain involved in emotion.
While fish lack the same emotional complexity of mammals and birds, the evidence implies they likely feel basic emotions and pain to some degree.
Reptiles and Amphibians: The Debate Continues
Reptilian Brain Structure
The reptilian brain, the most primitive part of vertebrate brains, controls basic functions like breathing, heart rate, and body temperature. Some experts argue that the simplicity of the reptilian brain indicates a lack of capacity for emotion.
However, others point out that even basic emotions require little brainpower. For example, fear responses are driven by the amygdala, a small, almond-shaped structure found even in reptile brains. So while reptile brains may be simple, they may still be capable of basic emotional experiences.
Observations of Turtle Behavior
Some interesting observations have been made about behaviors in turtles that seem emotional. One record described a captive tortoise that showed symptoms of grief after its mate died, including loss of appetite and lethargy. The tortoise only recovered after being given a new companion.
There have also been accounts of sea turtles appearing to cry while laying eggs. Tears may simply be a reflexive response, but some experts argue they indicate an overflow of emotion in a moment of stress.
Frog Warning Calls: Reflex or Feeling?
When detecting predators, frogs often emit warning calls to alert other frogs. Some believe these warning calls are purely reflexive, while others argue they are driven by alarm or fear.
In one controlled study, wood frogs were exposed to soggy wood chips giving the illusion of recent frog-eating snake activity. Frogs hearing the chips gave warning calls, suggesting the calls may be an impulsive, pre-programmed reaction to a snake scent rather than an emotional one.
Still, the debate continues around these behaviors in cold-blooded creatures. More research is needed to determine whether reflexes in amphibians and reptiles are paired with any capacity for emotion.
The Sentient Species: Birds and Mammals
Avian Intelligence
Recent research has shown that some birds, especially corvids (crows, ravens, jays) and parrots, demonstrate remarkable intelligence and problem-solving abilities that were once thought to be unique to humans and other primates (1).
Birds have shown the capacity for tool use, causal reasoning, imagination, deception, and even an understanding of death.
For example, New Caledonian crows will craft complex tools out of available materials to access food, rivaling the tool-making skills of great apes (2). African grey parrots like Alex and Einstein have learned hundreds of words and can combine them creatively to express desires and ask questions.
Mammalian Bonds and Emotion
In mammals, emotional bonds and feelings seem to arise from the limbic system, especially the amygdala and hippocampus (3). Dogs have been shown to experience jealousy, grief at the loss of a companion, contagious yawning that indicates empathy, and even display pride after completing a difficult task.
Great apes like chimpanzees form close family units and communities. When a chimpanzee dies, others will inspect the body and display aggressive behaviors towards unfamiliar chimps attending the funeral procession (4). This suggests mourning behaviors and awareness of death.
Measuring Animal Emotions
Despite compelling anecdotal evidence of animals exhibiting emotional behaviors, measuring subjective emotions scientifically remains challenging. Brain imaging technology has enabled observation of activity in emotion centers of animal brains.
Monitoring physiological signs like heart rate, adrenaline, and cortisol levels also provides clues.
Behavioral tests analyze reactions to stimuli. An experiment found cows experienced positive emotions when allowed to groom each other, suggesting friendship (5). Rats that freed trapped companions rather than obtain chocolate demonstrated empathy.
Conclusion
While we can’t ever know exactly what other creatures feel, scientific evidence points to some animals likely experiencing emotions in ways similar to humans. Mammals and birds appear to clearly demonstrate those capacities.
Meanwhile, simpler nervous systems make it doubtful that invertebrates, fish, amphibians and reptiles have subjective emotional experiences. But we still have more to understand about non-human inner lives. As we learn, we must continue ensuring animal welfare based on their cognitive complexity.
