The universe may be vast, but vision across all species might not be so different across cosmic distances.
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Summary: Human vision is tuned to the Sun’s spectral power density due to natural selection. Since stars across the universe emit peak radiation within a narrow range, extraterrestrial vision may share similarities with ours. The laws of physics and constraints of natural selection suggest common sensory adaptations in different environments, shaping how organisms perceive their surroundings.
One of earlier posts explored the characteristics of sensory perception related to vision and why they are the way they are.
Human eyes are sensitive to only a narrow segment of the electromagnetic (EM) spectrum — just 0.03% of its entirety. This vast spectrum ranges from gamma rays with the shortest wavelengths, measured in picometers, to radio waves that can stretch for kilometers.
The fact that our eyes respond specifically to this small slice of EM radiation is no coincidence. Their sensitivity is finely tuned to the spectral power density (SPD) of the Sun, which emits most of its radiation within the wavelengths our vision detects the best.
This precise alignment (or the case of hand fitting a glove) is the result of natural selection, an extraordinary force shaping biological evolution. A more effective ability to perceive the environment through vision offers a survival advantage, enhancing reproduction and ensuring the propagation of traits suited to environmental conditions. As a result, our vision evolved to detect the most abundant source of information in our surroundings.
Natural selection itself is no accident — given certain conditions, it is an inevitability. In an energy-constrained environment where organisms compete for survival, traits that enhance perception — such as sensitivity to the Sun’s preferred wavelengths — give a competitive edge. These advantageous traits persist across generations, reinforcing the logic behind natural selection’s role in shaping species.
Given this, one might wonder: If numerous other stars have SPDs similar to the Sun, would organisms evolving near them develop similar visual characteristics?
The answer lies in the variation of SPD among stars. Interestingly, the differences are not substantial. Stars in our galaxy are classified along the Main Sequence, with types ranging from O to M. This classification is primarily defined by surface temperature, which ranges from 30,000K in hot O-type stars to around 3,000K in cooler M-type stars.
A fundamental law of physics — Wien’s law — describes the inverse relationship between a star’s peak spectral power and its temperature. For example, hotter O-type stars emit peak radiation in the ultraviolet range, while cooler M-type stars peak in the infrared.
However, the range of peak SPD across Main Sequence stars — from ultraviolet to infrared — is relatively narrow compared to the full electromagnetic spectrum. This suggests that the physiology of vision among biological organisms across the universe may not differ dramatically.
To summarize:
- The fundamental laws of physics and stellar evolution dictate the wavelengths at which stars emit peak SPD is primarily within the ultraviolet-to-infrared range.
- Competition in energy-limited environments drives the emergence of natural selection.
- The combination of these factors implies that organisms evolving near different stars may develop comparable vision, shaped by the most abundant wavelengths of light available to them.
Perhaps that’s why, when Captain Kirk encounters extraterrestrial life aboard the Starship Enterprise, they often perceive reality in ways similar to humans.
A natural next question is: Why do star temperatures fall within the 3,000K to 30,000K range and not stretch to more extreme values? That would be another question worth exploring.
Ciao and thanks for reading.
Related:
- The worlds beyond my senses
- The reason I see and hear what I see and hear
- Fitting in a Puddle
- Why Do We Have Senses? Exploring the Evolution and Neuroscience Behind Human Perception
- How Biological Organisms Evolved Senses to Respond to Their Environment
- The Evolutionary Puzzle of Human Senses: Why Five?
- Senses and environment: Connecting the threads
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