Insects are conscious, egocentric beings, according to a new paper that also helps to explain why and likely when consciousness first evolved.

Recent neuroimaging suggests insects are fully hardwired for both consciousness and egocentric behavior, providing strong evidence that organisms from flies to fleas exhibit both.

Consciousness comes in many levels, and researchers say that insects have the capacity for at least one basic form: subjective experience.

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“When you and I are hungry, we don't just move towards food; our hunger also has a particular feeling associated with it," Colin Klein, who co-authored the new paper, told Discovery News. "An organism has subjective experience if its mental states feel like something when they happen."

Klein, a researcher at Macquarie University, and colleague Andrew Barron studied detailed neuroimaging reports concerning insect brains. They then compared the structure of such brains with those of humans and other animals. The resulting information is published in the journal Proceedings of the National Academy of Sciences.

Their work focused on the midbrain, a set of evolutionarily ancient structures that are surrounded by the gray folds of the cortex. The arrangement, they say, looks a bit like the flesh of a peach surrounding the pit.

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“In humans and other vertebrates (animals with a backbone and/or spinal column) there is good evidence that the midbrain is responsible for the basic capacity for subjective experience," Klein said. “The cortex determines much about what we are aware of, but the midbrain is what makes us capable of being aware in the first place. It does so, very crudely, by forming a single integrated picture of the world from a single point of view."

Portions of insect brains work in a similar way to the midbrain in humans, performing the same sort of modeling of the world, the authors believe.

As for being egocentric, Barron explained that there is now compelling evidence that insects display selective attention to their processing of the world.

“They don't pay attention to all sensory input equally," Barron explained. "The insect selectively pays attention to what is most relevant to it at the moment, hence (it is) egocentric."

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The term “insect" is a broad one, generally referring to any small animal that has six legs, a body formed of three parts, and may have wings. Since diverse species under this umbrella term have widely varying sensory systems and ways of life, the authors expect that to be reflected in their conscious lives.

Not all living things are thought to have consciousness, though. Plants, for example, do not have the necessary structures for it. Jellyfish and nematodes (certain unsegmented worms, such as roundworms) do not have such hardwiring either.

Barron and Klein believe the origins of consciousness date to the Cambrian or even to the Precambrian Periods (more than 600 years ago).

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“When organisms began to move freely in their environment, they faced many new challenges," Klein explained. “They had to decide where to go next. They had to prioritize their needs. They had to interpret sensory information that changed as a consequence of their motion. That required a new kind of integrated modeling, and that's where we think consciousness arose.

Bruno van Swinderen is an associate professor at the University of Queensland and is a leader in the field of insect neurobiology.

Van Swinderen told Discovery News that one of the most important points of the new paper is the realization that understanding the evolution of consciousness will not come from looking for intelligent behavior in other animals, but rather from understanding the fundamental mechanisms that support subjective awareness and selective attention, which he said “we now know insects have."

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“Insects have traditionally been viewed as mini robots, responding to environmental stimuli in a rather inflexible way," he continued. “In contrast, Barron and Klein suggest that it is likely that some of the fundamental underpinnings of consciousness have already been solved in even the smallest brains."

Completely understanding what's on the mind of an insect is still impossible, however.

As Klein said, “In some sense it's very hard to understand what other people experience, much less animals! But we think that research can reveal much about the contents of insects' experience, as well as the similarities and differences in the way that these experiences are structured."