Although scientific research about consciousness has enjoyed a boom in the past two decades, one central question remains unanswered: What is the function of consciousness? Why did it evolve at all?

The answers to these questions are crucial to understanding why some species (such as our own) became conscious while others (such as oak trees) did not. Furthermore, observing the brains of birds shows that evolution can achieve similar functional solutions to realize consciousness despite different structures.

The working groups led by Professors Albert Newen and Onur Güntürkün at Ruhr University Bochum, Germany, report their findings in a current special issue of the journal Philosophical Transactions of the Royal Society B: Biological Sciences from November 13, 2025.

Purposes of pleasure and pain?
Our conscious experience makes up our lives, often through positive pleasure: I feel the warm sun on my skin, I hear the singing of birds, I enjoy the moment. Yet we also often experience pain: I feel my knee hurt from falling on the stairs, I suffer from always being pessimistic. Why have we, as living creatures, even developed a perception that can involve positive experiences as well as pain and even unbearable suffering?

Albert Newen and Carlos Montemayor categorize three types of consciousness, each with different functions: basic arousal, general alertness, and a reflexive (self-)consciousness.

"Evolutionarily, basic arousal developed first, with the base function of putting the body in a state of ALARM in life-threatening situations so that the organism can stay alive," explains Newen. "Pain is an extremely efficient means for perceiving damage to the body and to indicate the associated threat to its continued life. This often triggers a survival response, such as fleeing or freezing."

A second step in evolution is the development of general alertness. This allows us to focus on one item in a simultaneous flow of different information. When we see smoke while someone is speaking to us, we can only focus on the smoke and search for its source.

"This makes it possible to learn about new correlations: first the simple, causal correlation that smoke comes from fire and shows where a fire is located. But targeted alertness also lets us identify complex, scientific correlations," says Carlos Montemayor.

Humans and some animals then develop a reflexive (self-)consciousness. In its complex form, it means that we are able to reflect on ourselves as well as our past and future. We can form an image of ourselves and incorporate it into our actions and plans.

"Reflexive consciousness, in its simple forms, developed parallel to the two basic forms of consciousness," explains Newen. "In such cases, conscious experience focuses not on perceiving the environment, but rather on the conscious registration of aspects of oneself."

This includes the state of one's own body, as well as one's perception, sensations, thoughts, and actions. To use one simple example, recognizing oneself in the mirror is a form of reflexive consciousness.

Children develop this skill at 18 months, and some animals have been shown to do this as well, such as chimpanzees, dolphins, and magpies. Reflexive conscious experiences—as its core function—makes it possible for us to better integrate into society and coordinate with others.