Month: September 2025

Long insect muscle: an evolutionary relic of the wrist

When you extend your hand with your thumb and pinky facing each other and gently bend your wrist backward, about 85% of people will notice a thin, long, band-like bulge in the middle of their wrist. This muscle, called the palmaris longus , plays almost no role in modern humans, but it’s a defining relic of human evolution.

The long worm muscle is highly developed in many quadrupedal primates, such as monkeys, which rely on their forelimbs for support and frequently perform large wrist flexions. As humans began walking upright, the weight-bearing load borne by their forelimbs decreased significantly, and the long worm muscle gradually degenerated. In modern humans, approximately 15% of people completely lack this muscle without any impact on their daily lives. This suggests that even if certain organs or muscles degenerate functionally, they remain in the genome, becoming “historical traces” of evolution.

Piloerection: The physiological significance of goose bumps

Goose bumps are a common piloerection reaction in almost all land mammals . This reaction is caused by the contraction of small muscles under the skin, causing the hair to stand upright. Its physiological functions mainly include two aspects:

Keeping warm : When the ambient temperature drops suddenly, the hair stands up to increase the thickness of the insulation layer and slow down the loss of body heat.

Self-defense : When threatened or frightened, the hair stands up to make the body appear larger, thus deterring potential enemies.

During the process of human evolution, body hair gradually became sparse and the function of piloerection reaction was no longer significant, but its existence still reflects the survival strategy of early mammals.

The grasping reflex: Infants’ primitive survival mechanism

Infants develop a palmar grasp reflex within a few months of birth : when their palms touch an object, their fingers automatically clench. This reaction is similar to the way primates cling to their mother’s womb or back, and is a completely unconscious survival mechanism.

Although modern human infants no longer need to grasp to escape predators or cling to their mothers, this reflex remains in their genes, reflecting a legacy of an evolutionary survival safety strategy.

Semi-vestigial organs: appendix, tonsils, and wisdom teeth

There are also some typical semi-degenerate organs in the human body:

Appendix : Early humans consumed large amounts of plant fiber, and the appendix served to break down indigestible substances. As cooked food and cooking techniques became more common, the appendix’s function gradually weakened.

Tonsils : Originally used to filter bacteria entering the mouth, their independent function gradually degenerates as the body’s immune system improves.

Wisdom teeth (third molars) : Due to the shrinkage of the human jaw and the insufficient depth of the oral cavity, wisdom teeth often cannot erupt normally.

The existence of these organs shows the gradual weakening of organ functions during human evolution, and also provides an evolutionary explanation for medicine.

Reverse inhibition: sporadic expression of recessive genes

In some cases, features that have degenerated or disappeared can occasionally reappear, a phenomenon known as atavism . Typical examples include:

Tail : Although the human tail is vestigial, the coccyx still exists, and a very small number of babies are born with a movable tail.

Movable ears : About 15% of people can move their ears. This is because the anterior auricular muscles, superior auricular muscles and posterior auricular muscles have almost degenerated during the long process of evolution, but a few people still retain a certain degree of mobility.

Werewolf syndrome : Some people are born with an abnormal increase in body hair or extra ribs in the cervical spine, which is also a counter-resistance phenomenon.

The sporadic appearance of these traits suggests that the relevant genes have not been completely eliminated but are instead expressed through recessive or diluted genes.

Traces of evolution in embryonic development

Human embryos briefly develop a tail during their sixth week of development. This tail is then resorbed during subsequent development, leaving only the coccyx as a relic. If the genes responsible for the coccyx mutate or are otherwise misexpressed, the tail may persist until birth. This process illustrates the crucial role of gene regulation in evolution, determining which traits are retained and which are eroded or hidden.

Furthermore, early human embryos closely resemble other mammals in morphology, such as heart position, limb structure, and tail morphology. This phenomenon emphasizes the gradualness and commonality of evolution and provides an important basis for comparative anatomy and embryology studies.

Other evolutionary relics in the human body

In addition to the examples above, the human body also retains other more common traces of evolution:

Muscles around the ears : Most of the functions of the anterior auricular muscles, superior auricular muscles and posterior auricular muscles that can adjust the direction of the ear have degenerated.

Hair and body hair : Body hair is significantly reduced, but abnormal growth still occurs in a very small number of individuals.

Extra ribs in the neck : called cervical ribs, are an evolutionary remnant that are occasionally visible at birth.

These characteristics indicate that during the long process of human evolution, many organs and functions are in a semi-degenerate state. Their existence is not only physiological evidence, but also provides intuitive material for studying human evolution.

The scientific significance of evolutionary traces

These remaining organs and functions in the human body have important scientific value:

Understanding evolutionary mechanisms : By observing semi-degenerate organs and counter-resistance phenomena, we can trace the path of human evolution and understand the evolution of physiological functions.

Medical and physiological research : The evolutionary background of organs such as the appendix, wisdom teeth, and tonsils helps explain the mechanisms of disease and the necessity of surgery.

Behavior and survival strategies : Functions such as piloerection and grasping reflex reveal the early living environment and behavioral adaptations of humans.

These phenomena remind people that even though modern life has been separated from the natural environment, the human body still retains the imprint of evolutionary history. These “historical traces” are important windows for understanding biology and medicine.

Modern Enlightenment and the Value of Popular Science

Studying the traces of human evolution not only facilitates academic inquiry but also fosters public interest in science. Many people mistakenly believe that evolution is irrelevant to everyday life. However, by observing features like worm muscles, the grasping reflex, and the piloerection response, we can intuitively perceive tangible evidence of evolution. These vivid and accessible examples serve as valuable material for science education and popularization.

At the same time, these evolutionary relics remind us of the limitations of scientific understanding and historical biases. Humans have developed complex mechanisms for adapting to their environment and to themselves. Modern science is constantly decoding these mechanisms, correcting past misunderstandings and providing a theoretical foundation for future medical and biological research.

Theory of Born Criminal in 19th Century Europe

In 19th-century Europe, a popular way of thinking, which used facial and cranial features to judge a person’s personality and criminal tendencies, became known as Cesare Lombroso’s Criminal Anthropology . Its originator, Cesare Lombroso, is considered the “Father of Modern Criminology” in the history of criminology.

The core idea of the born criminal theory is that some criminals, especially serious criminals, are driven by nature to commit crimes. Their genes carry a so-called “savage tendency,” which manifests in primitive, violent behavior patterns. This view attempts to explain crime through biology, and its supposed scientific basis comes from a discipline called phrenology.

The origin and development of phrenology

Phrenology was founded by Franz Joseph Gall, a German neurologist in the early 19th century. While working in a mental hospital, Gall noticed similarities in the shapes of the heads of patients with mental illness. He hypothesized that personality, intelligence, and psychological traits might be linked to head shape. To test this theory, Gall began collecting skulls from various sources, including those of the mentally ill, criminals, and historical figures.

Through his research, he proposed the theory of brain compartmentalization, positing that different brain regions are independent and correspond to distinct personality traits. The more developed a particular brain region, the more pronounced the corresponding personality trait is in the individual, and this trait can influence the appearance of the skull. For example, a more developed region can make the skull more prominent, resulting in measurable features. Gall also created a model of the head compartmentalization, labeling the personality traits associated with each region, and designed an instrument to measure skull shape for direct qualitative analysis.

The combination of born criminal theory and phrenology

Lombroso combined phrenology with criminology to develop the concept of the “born criminal.” He identified a series of facial and head features that he claimed were associated with a high propensity to commit crimes, including:

Facial asymmetry

groin nose

big chin

high cheekbones

Flat forehead

Raised brow bone

Big Ears

Sparse body hair

By analyzing the skulls of hundreds of death row inmates, he concluded that approximately 40% of criminal behavior stems from these “innate” head features. This theory was not only used in criminological research, but was also attempted to be applied in investigations and criminal convictions.

Phrenology, racism, and aesthetic prejudice

Phrenology and the theory of born criminals were widely disseminated in Europe at the time, benefiting from prevalent racist ideologies. Researchers linked skull morphology to intelligence and personality across different races, even proposing an “evolutionary gap” between Blacks and Whites, arguing that some races were closer to a primitive state. This view not only lacked scientific basis but also disguised aesthetic bias and racial discrimination as “scientific discovery.”

In fact, many of the “criminal facial features” defined by Lombroso and Gall were based on the aesthetic judgments of the time rather than on biological associations with actual criminal behavior. The logic that individuals deemed “ugly” are more likely to be labeled criminal suspects is clearly seriously flawed.

Theoretical limitations and judicial responses

Despite its popularity among the public and some academic circles, the theory of born criminals has not been widely accepted in judicial practice. One reason is that the theory is too broad and can easily be used by defendants as an excuse. For example, some criminals may claim that their criminal behavior is driven by “innate violent genes,” thereby blurring the lines between personal responsibility.

With the development of scientific methods, phrenology and the theory of born criminals have been gradually discredited as pseudoscience. Modern neurology and criminal psychology indicate that criminal behavior is more influenced by social, psychological, and environmental factors than simply genetics or skull morphology. Modern criminological research has found that family environment, education level, social pressure, and neurochemical factors have a more direct impact on criminal behavior. For example, early traumatic experiences and social rejection are often more predictive of adolescent criminal tendencies than genetic factors.

Contemporary Perspective: Cognitive Biases and Pseudoscience Traps

Although phrenology and the theory of born criminals have long been outdated, the human cognitive patterns they reflect are still worth noting. 200 years ago, those who believed that skull shape determined personality had similar thinking patterns to those who believe in horoscopes, conspiracy theories, or quick psychological tests today:

Tend to use simple logic to explain complex phenomena

Seeking certainty and predictability

Avoid deep analysis and embrace uncertainty

This cognitive bias persists today, especially in the rapidly disseminating online environment. Pseudoscience, conspiracy theories, and inflammatory rhetoric often exploit the human need for “simple patterns” to mislead or manipulate the public. Understanding historical phrenology and the theory of born criminal can help us better identify modern information traps and improve our critical thinking skills.

Supplementary historical cases and cultural influences

The theory of born criminals also had a long-lasting impact on society and culture. This trend of thought can be seen in many detective novels and literary works from the late 19th century to the early 20th century. For example, the descriptions of criminals’ appearance and psychology in the detective stories of French author Edgar Allan Poe and the novels of British author Sherlock Holmes were partly influenced by contemporary theories of phrenology and criminal biology. Furthermore, this “appearance determines character” approach also influenced some early police records, leading law enforcement officials to subconsciously bias their case analysis.

Lessons and Reflections

The popularity of born criminal theory and phrenology reveals the risks of intertwining scientific and social biases. They remind us that:

Science must be based on rigorous evidence , not visual impressions or aesthetic judgments.

Cognitive biases can affect decision-making at any time , especially when it comes to evaluating the behavior of others.

Historical cases can serve as cautionary tales , helping us understand how contemporary society can combat pseudoscience and bias in information dissemination.

Comparing the past and present, humans still need to be wary of the misleading effects of simplistic logic and cognitive shortcuts. The complexity of society means that individual behavior cannot be judged solely by appearance or a single characteristic. The scientific spirit demands constant questioning and deep understanding.

Conclusion

The story of born-again criminal theory and phrenology is not only a history of science but also a reflection on human cognition, biases, and societal beliefs. In modern society, where information dissemination and public opinion are increasingly rapid and complex, understanding these historical lessons can help cultivate critical thinking and avoid falling into pseudoscience and cognitive traps. Perhaps we should reflect on which seemingly plausible claims in today’s online landscape are actually repeating cognitive misconceptions from 200 years ago?

The Fantasy Test: Human Sensitivity to Faces

Even if a photo of a face has been blurred, it can still be recognized by most people. This is because humans are extremely sensitive to facial features. In contrast, when presented with inanimate objects, people often see patterns resembling faces in them, such as cracks in a wall, the shape of clouds, and even the arrangement of furniture. This phenomenon is known in psychology as pareidolia . Simply put, the human brain tends to recognize familiar objects in visual information that are not actually there, especially faces.

The imaginativeness test not only explains the widespread cross-cultural use of emojis, but also reveals the peculiarities of the human visual system. Even with blurry or incomplete facial information, the brain attempts to match it to an existing facial template, resulting in the perception of a “face.” This phenomenon is ubiquitous in everyday life: people often say they see a “face in the moon” or “car headlights that look like eyes,” which is actually the brain executing a facial recognition pattern.

Visual Information Processing: Perception and Recognition

The process by which humans see things can be divided into two core steps: perception and recognition .

Perception stage : After light enters the eye, the retina converts it into electrical signals and transmits them to the visual cortex in the occipital lobe of the brain. At this stage, the brain only receives image information but has not yet understood its content.

Recognition stage : The brain’s visual cortex then extracts key features from the image and passes them to the fusiform gyrus . This brain region is specialized for object recognition, with the right side of the gyrus specifically processing facial information. This mechanism is similar to modern facial recognition algorithms: the brain first determines which areas are likely to be faces and sets a similarity threshold. Patterns that exceed this threshold trigger the perception of “face-likeness.”

The basic features of facial recognition are simple: an inverted triangle structure, symmetrical eyes, and a slightly larger mouth. Images that meet this basic composition easily activate the imaginary testing mechanism. More specific or realistic facial information is then compared with the brain’s existing facial templates, allowing for identification.

The importance of facial recognition: an evolutionary perspective

Humans’ sensitivity to faces is not accidental, but the result of long-term evolution. Facial recognition is crucial for social behavior:

Identify individuals : determine their identity

Interpreting emotions : Judging friendliness, hostility, or fear through facial expressions

Guide behavior : adjust social strategies and respond appropriately

In contrast, other objects, such as hands or cups, do not activate the brain’s preferential recognition mechanism. Faces are so important to humans because vision is our primary sensory tool, not smell or touch (unlike some mammals or insects). Complex social structures and the need for cooperation further enhance facial recognition, making it a priority type of information processed in the brain.

Historically, this ability was likely closely linked to early humans’ survival in groups. In early tribal life, accurately identifying companions, enemies, or potential threats had a direct impact on individual survival. Consequently, the brain evolved mechanisms that are highly sensitive to facial features, enabling rapid recognition even when faces are incomplete or damaged.

Prosopagnosia: A variation in facial recognition ability

Although most people are born with the ability to recognize faces, approximately 2% of the population suffers from congenital face blindness (prosopagnosia) . These people have a weak fusiform gyrus, which results in limited facial recognition:

Mild patients : can recognize faces, but have difficulty remembering detailed features and are easily confused with people who look similar.

Severe patients may not be able to recognize basic facial structures, or even inverted triangle compositions. Faces they see may look like “objects” to them, such as mops or wall patterns.

People with face blindness often rely on hairstyle, clothing, or voice for auxiliary recognition, making them difficult to detect in daily life. This difference in ability shows that even with highly developed facial recognition mechanisms, there are significant individual differences.

Face recognition and social interaction

Facial recognition is more than just a visual ability; it’s a core tool for social adaptation. In complex social environments, humans must quickly interpret others’ identities, intentions, and emotions to determine interaction strategies. Subtle changes in facial expressions, smiles, frowns, and other expressions provide a wealth of information that directly impacts survival and cooperation.

Modern technology is also emulating this ability. For example, AI facial recognition systems are now widely used for security surveillance, smartphone unlocking, and photo tagging for social media. While these algorithms can recognize faces, their understanding of micro-expressions, emotions, or social cues is far inferior to the human brain. This demonstrates that the complexity of human facial recognition far exceeds current technology.

It’s worth noting that facial recognition abilities also exist at varying levels in the animal world. Primates, for example, can distinguish individuals based on facial expressions, while some birds can even recognize faces of their own species and memorize social relationships over many years. This further demonstrates that facial recognition abilities are closely linked to social needs.

Summary and Thoughts

Humans’ heightened sensitivity to faces is the result of a combination of visual processing, evolutionary adaptation, and social needs. From imaginary tasks to real-life face recognition, the brain, through the fusiform gyrus, transforms visual information into social cognition, supporting complex social behaviors. Prosopagnosia reveals individual differences in this ability, reminding us that facial recognition cannot be taken for granted.

In the future, as AI technology develops, how humans and intelligent systems process facial information together will pose new challenges to privacy, social interaction, and ethics. It’s also worth considering how facial recognition capabilities will evolve in modern social networks and virtual environments.

Display and Real World: Differences in Color Representation

In everyday life, the colors we see aren’t exactly the same as those displayed on screen. For example, yellow appears in the real world because objects absorb light outside the yellow wavelength range, reflecting only light with wavelengths between approximately 570 and 590 nanometers to the human eye. However, the yellow on a screen isn’t directly emitted by yellow light. Instead, it’s produced by a combination of red, green, and blue primary color pixels at varying brightness levels. When the blue light’s brightness is reduced, the remaining red and green mixture is perceived by the brain as yellow.

The essence of this phenomenon lies in the human visual system. The retina contains three types of cone cells, responsible for sensing light: long-wavelength (red), medium-wavelength (green), and short-wavelength (blue). Yellow light, with a wavelength between red and green, activates both red and green cones, resulting in a yellow perception. Displays achieve the same effect by adjusting the brightness of red and green pixels, creating a similar color experience in the brain.

The Nature of Object Color: Electronic Transitions and Light Absorption

The color of an object is essentially the result of the interaction between the molecular structure of the material’s surface and light. Electrons in the outer shell of an atom operate stably in a low-energy state, known as the ground state. When these electrons absorb sufficient energy, they transition to a higher-energy orbital. This excitation process absorbs energy from light. Different colors of light have different energies, with shorter wavelengths having higher energy. Electrons only absorb light waves with a matching transition energy; the rest is reflected.

For example, if the energy required for an electron transition matches that of blue light, it will absorb blue light and reflect other light. The combination of these reflected light forms the color we perceive. For example, an object reflects red and green light but absorbs blue light, resulting in a yellow appearance. This shows that color is not an inherent property of an object but rather the result of the interaction between electron transitions and light, combined with the retina’s interpretation of light, which creates a subjective perception.

Visual evolution and biological color perception

Humans have three types of cone cells, which are not particularly common among mammals. Most mammals have only two types of cone cells, resulting in a relatively narrow range of color perception. This is related to the nocturnal nature of mammalian ancestors, which led them to evolve a visual system sensitive to light intensity and less sensitive to color. To compensate for their limited color vision, mammals have developed robust senses of smell and hearing, enabling them to effectively perceive the world in nocturnal environments.

In contrast, birds’ visual cells are more complex, sensing not only red, green, and blue, but also violet and some ultraviolet light. This allows birds to discern a wider range of colors, enabling them to use them for courtship, warnings, and ecological communication. The greater the variety of visual cells, the richer and more vibrant the color perception. For example, the plumage colors of tropical birds evolved as visual signals specifically for ecological and social functions.

Mantis shrimp: A world of color beyond humankind

Mantis shrimp have the most advanced color vision in the animal kingdom. They possess 12 photoreceptors, four times as many as humans, capable of sensing light from red to ultraviolet, and even polarized light. However, their visual paradigm differs from that of humans; their color vision is more like a discrete channel system. While humans can distinguish colors with wavelengths differing by about 4 nanometers, the minimum resolvable wavelength difference for mantis shrimp is about 25 nanometers. This means their vision is more like selectively locking onto specific wavelengths of the spectrum to quickly capture prey, rather than integrating continuous color information.

The existence of this unique visual system highlights the adaptive evolution of color across species. Mantis shrimp rely on highly precise light perception for both hunting and survival, and their visual abilities directly influence their survival strategies. Human trichromatic color vision, on the other hand, plays a crucial role in discerning subtle differences in fruit and the environment.

Optical Principles and Structural Color

In addition to the colors produced by chemical pigments, structural color also occurs in nature. Structural color occurs through the interference of light through microscopic surface structures, causing specific wavelengths to reflect and create color. Examples include the blue or green sheen of blue morpho butterflies and peacock feathers. The rarity of blue is related to the complexity of its molecular structure. The complex conjugated double bond system absorbs long-wavelength light and reflects short-wavelength light, but the molecules are unstable and rarely occur naturally. Structural color provides a non-pigmented visual expression and is often used in ecological behaviors such as courtship, warning, and group recognition.

Chemical pigments and conjugated double bond systems

The appearance of chemical pigments depends on the conjugated double bond system within the molecule—a structure characterized by alternating single and double bonds. The greater the number of conjugated double bonds, the longer the wavelength of light the molecule can absorb, and the color shifts toward the blue end. However, the more complex the molecular structure, the lower its stability and the less likely it is to occur naturally. For example, retinol molecules absorb blue-violet light and appear orange-yellow, while synthetic titanium blue pigments require complex processes involving high temperatures and high pressures to achieve a stable blue color.

The evolutionary significance of human color vision

Human trichromatic vision may be a result of later evolution, providing an advantage for identifying ripe fruit or plant maturity. In contrast, mammals have evolved dichromatic vision, which is advantageous for nocturnal travel, while birds and insects, which require more advanced color vision for ecological signals and courtship behaviors, have developed multiple cone cell types and structural color perception capabilities. This diverse visual system reveals the complexity of biological adaptive evolution.

Summarize

Color is the product of the interaction between an object’s molecular structure and light, and the result of the biological visual system’s interpretation of light waves. From the yellow we see on a display screen to the wings of a blue morpho butterfly in nature, every color is rooted in physical, chemical, and biological principles. Human trichromatic vision, bird tetrachromatic vision, and the 12-color perception of mantis shrimp reveal how the evolution of vision is closely linked to ecology, courtship, and survival strategies. Understanding these principles can provide a deeper understanding of the wonders of color in nature and the unique way humans perceive the world.