The ship of Theseus is a thought experiment that raises the question of whether a ship that has had all of its components replaced remains fundamentally the same object.

Suppose that the famous ship sailed by the hero Theseus in a great battle has been kept in a harbour as a museum piece. As the years go by some of the wooden parts begin to rot and are replaced by new ones. After a century or so, all of the parts have been replaced. Is the “restored” ship still the same object as the original?

{ Wikipedia | Continue reading }

Does the Human Body Really Replace Itself Every 7 Years?

Recent research has confirmed that different tissues in the body replace cells at different rates, and some tissues never replace cells. So the statement that we replace every cell in the body every seven years or every ten years is wrong. […]

Neurons in the cerebral cortex are never replaced.

Fat cells are replaced at the rate of about 10% per year in adults. […]

Cardiomyocyte cells [muscle cells of the heart] are replaced at a reducing rate as we age. At age 25, about 1% of cells are replaced every year. Replacement slows gradually to about 0.5% at age 70. Even in people who have lived a very long life, less than half of the cardiomyocyte cells have been replaced. Those that aren’t replaced have been there since birth.

{ Ask a Naturalist | Continue reading }

Your lungs are six weeks old - and your taste buds just ten days! […]

Liver cells only have a life span of around 150 days. […] “I can take 70 per cent of a person’s liver away in an operation and around 90 per cent of it will grow back within two months,” explains David Lloyd, consultant liver surgeon at Leicester Royal Infirmary. […]

Your eyes are one of the few body parts that don’t really change during your life. The only part that is constantly being renewed is the cornea, the transparent top layer.

{ Daily Mail | Continue reading }

A collection of the replacement rates of different cells in our body:

[…]

We note that hair elongates at about 1 cm per month while fingernails grow at about 0.3 cm per month, which is about the same speed as the continental spreading in plate tectonics that increases the distance between North America and Europe.

{ Cell Biology by the Numbers | Continue reading }

For decades, scientists believed that neurogenesis—the creation of new neurons—whirs along nicely in the brains of embryos and infants, but grinds to a halt by adulthood. But from the 1980s onward, this dogma started to falter. Researchers showed that neurogenesis does occur in the brains of various adult animals, and eventually found signs of newly formed neurons in the adult human brain. Hundreds of these cells are supposedly added every day to the hippocampus—a comma-shaped structure involved in learning and memory. The concept of adult neurogenesis is now so widely accepted that you can find diets and exercise regimens that purportedly boost it.

The trouble is: This stream of fresh neurons might not actually exist.

In a new study, and one of the biggest yet, a team led by Arturo Alvarez-Buylla at the University of California at San Francisco completely failed to find any trace of young neurons in dozens of hippocampus samples, collected from adult humans.

{ The Atlantic, March 2018 | Continue reading }

People as old as 79 may still generate new brain cells, US researchers said Thursday. […] Using autopsied brain samples from 28 people who died suddenly between the ages of 14-79, researchers looked at “newly formed neurons and the state of blood vessels within the entire human hippocampus soon after death.” […]

A study last month led by Arturo Alvarez-Buylla of the University of California in San Francisco found the opposite, however.

{ Medical Express, April 2018 | Continue reading }

The generation of cells in the human body has been difficult to study, and our understanding of cell turnover is limited. Testing of nuclear weapons resulted in a dramatic global increase in the levels of the isotope 14C in the atmosphere, followed by an exponential decrease after 1963.

We show that the level of 14C in genomic DNA closely parallels atmospheric levels and can be used to establish the time point when the DNA was synthesized and cells were born. We use this strategy to determine the age of cells in the cortex of the adult human brain and show that whereas nonneuronal cells are exchanged, occipital neurons are as old as the individual, supporting the view that postnatal neurogenesis does not take place in this region.

{ Cell | PDF }

If the cells of our skin are replaced regularly, why do scars and tattoos persist indefinitely?

The cells in the superficial or upper layers of skin, known as the epidermis, are constantly replacing themselves. This process of renewal is basically exfoliation (shedding) of the epidermis. But the deeper layers of skin, called the dermis, do not go through this cellular turnover and so do not replace themselves. Thus, foreign bodies, such as tattoo dyes, implanted in the dermis will remain.

{ Scientific American | PDF }

inkjet and acrylic on canvas { imp kerr (b.1980), not confirmed as alive, 59th st, nyc, 1977, 2018 }

On Friday, representatives of more than 60 nations, gathered in Versailles, France, approved a new definition for the kilogram.

Since the 19th century, scientists have based their definition of the fundamental unit of mass on a physical object — a shining platinum iridium cylinder stored in a locked vault in the bowels of the International Bureau of Weights and Measures (BIPM) in Sevres, France. A kilogram was equal to the heft of this aging hunk of metal, and this cylinder, by definition, weighed exactly a kilogram. If the cylinder changed, even a little bit, then the entire global system of measurement had to change, too.

With Friday’s vote, scientists redefined the kilogram for the 21st century by tying it to a fundamental feature of the universe — a small, strange figure from quantum physics known as Planck’s constant, which describes the smallest possible unit of energy. […]

Though the newly defined kilogram won’t affect your bathroom scale, it will have practical applications in research and industries that depend on meticulous measurement. […]

The kilogram prototype, known as “Le Grand K,” was made by humans and is subject to all our limitations. It is inaccessible — the safe containing the cylinder can be opened only by three custodians carrying three separate keys, an event that has happened fewer than a dozen times in the object’s 139-year history. And it is inconsistent — when Le Grand K was examined in the 1980s, it weighed several micrograms less than it was supposed to. This meant that anyone who made products based on the standards had to reissue their weights. Manufacturers were furious. Lawmakers were called. Metrologists, people who study measurements, were accused of incompetence.

So, in a 2014 meeting at the BIPM, the metrology community resolved to redefine the kilogram. 

{ Washington Post | Continue reading }

On April 7, 1795, the gram was decreed in France to be “the absolute weight of a volume of pure water equal to the cube of the hundredth part of the metre, and at the temperature of melting ice.”

Since trade and commerce typically involve items significantly more massive than one gram, and since a mass standard made of water would be inconvenient and unstable, the regulation of commerce necessitated the manufacture of a practical realization of the water-based definition of mass. Accordingly, a provisional mass standard was made as a single-piece, metallic artifact one thousand times as massive as the gram—the kilogram.

At the same time, work was commissioned to precisely determine the mass of a cubic decimetre (one litre) of water. Although the decreed definition of the kilogram specified water at 0 °C—its highly stable temperature point—the French chemist Louis Lefèvre-Gineau and the Italian naturalist Giovanni Fabbroni after several years of research chose to redefine the standard in 1799 to water’s most stable density point: the temperature at which water reaches maximum density, which was measured at the time as 4 °C. They concluded that one cubic decimetre of water at its maximum density was equal to 99.9265% of the target mass of the provisional kilogram standard made four years earlier.

That same year, 1799, an all-platinum kilogram prototype was fabricated with the objective that it would equal, as close as was scientifically feasible for the day, the mass of one cubic decimetre of water at 4 °C. The prototype was presented to the Archives of the Republic in June and on December 10, 1799, the prototype was formally ratified as the kilogramme des Archives (Kilogram of the Archives) and the kilogram was defined as being equal to its mass.

{ Wikipedia | Continue reading }

Only three countries—Burma (Myanmar), Liberia, and the US—have not adopted the International System of Units as their official system of weights and measures.

{ Mental Floss | Continue reading }

Try this experiment: Pick a famous movie—Casablanca, say—and summarize the plot in one sentence. Is that plot you just described the thing you remember most about it? Doubtful. Narrative is a necessary cement, but it disappears from memory.

{ Peter Greenaway | Continue reading }

“I almost always remember where I was and I remember the book itself. I remember the physical object,” says Paul, the editor of The New York Times Book Review, who reads, it is fair to say, a lot of books. “I remember the edition; I remember the cover; I usually remember where I bought it, or who gave it to me. What I don’t remember—and it’s terrible—is everything else.” […] “Memory generally has a very intrinsic limitation,” says Faria Sana, an assistant professor of psychology at Athabasca University, in Canada. “It’s essentially a bottleneck.” The “forgetting curve,” as it’s called, is steepest during the first 24 hours after you learn something. Exactly how much you forget, percentage-wise, varies, but unless you review the material, much of it slips down the drain after the first day, with more to follow in the days after, leaving you with a fraction of what you took in.

{ The Atlantic | Continue reading }

Brooklyn-based blockchain software technology startup and Ethereum development studio ConsenSys has acquired asteroid mining company Planetary Resources, Inc. through an asset-purchase agreement. […]

ConsenSys is a production studio that creates enterprises in a wide range of business areas based on the Etherium platform for cryptocurrency and other blockchain applications. It has spawned 50 ventures, or “spokes,” including an online poker site, a legal services site and a “transmedia universe integrated with blockchain technology” called Cellarius. […]

Planetary Resources was founded in its present form in 2012, with initial backing from billionaires including Larry Page, Eric Schmidt, Ross Perot Jr. and Charles Simonyi. Its original mission was to identify and mine near-Earth asteroids for valuable resources, ranging from water that could be converted into rocket fuel to platinum-group metals that could conceivably be sent back to Earth.

Over the course of six years, the venture raised tens of millions of dollars and explored other potential revenue streams, including space telescope manufacturing, space selfies and an Earth-observation constellation called Ceres. […] But an anticipated funding round failed to come together, leading to a wave of staff cutbacks.

{ GeekWire | Continue reading }

related { Cryptocurrency Pump-and-Dump Schemes }

photo { Model of a Tyrannosaurus Rex, 1936 }

The Principia Mathematica (PM) is a three-volume work on the foundations of mathematics written by Alfred North Whitehead and Bertrand Russell and published in 1910, 1912, and 1913.

was an attempt to describe a set of axioms and inference rules in symbolic logic from which all mathematical truths could in principle be proven.

PM has long been known for its typographical complexity. Famously, several hundred pages of PM precede the proof of the validity of the proposition 1+1=2.

{ Wikipedia | Continue reading }

Previous studies have shown that male attractiveness can be enhanced by manipulation of status through, for example, the medium of costume. The present study experimentally manipulated status by seating the same target model (male and female matched for attractiveness) expressing identical facial expressions and posture in either a ‘high status’ (Silver Bentley Continental GT) or a ‘neutral status’ (Red Ford Fiesta ST) motor-car. […]

Results showed that the male target model was rated as significantly more attractive on a rating scale of 1–10 when presented to female participants in the high compared to the neutral status context. Males were not influenced by status manipulation, as there was no significant difference between attractiveness ratings for the female seated in the high compared to the neutral condition.

{ The British Psychological Society | PDF }

unrelated { Sweden plans to make sex toys safer because so many people get them stuck in their rectum }

Because more and more young people are constantly presented with the opportunity to access information and connect to others via their smartphones, they report to be in a state of permanent alertness. In the current study, we define such a state as smartphone vigilance, an awareness that one can always get connected to others in combination with a permanent readiness to respond to incoming smartphone notifications. We hypothesized that constantly resisting the urge to interact with their phones draws on response inhibition, and hence interferes with students’ ability to inhibit prepotent responses in a concurrent task. […]

Results show that the mere visibility of a smartphone is sufficient to experience vigilance and distraction, and that this is enhanced when students receive notifications. Curiously enough, these strong experiences were unrelated to stop-signal task performance. These findings raise new questions about when and how smartphones can impact performance.

{ PsyArXiv | Continue reading }

Procrastination is a familiar and widely discussed proclivity: postponing tasks that can be done earlier. Precrastination is a lesser known and explored tendency: completing tasks quickly just to get them done sooner.

Recent research suggests that precrastination may represent an important penchant that can be observed in both people and animals.

{ Learning & Behavior | Continue reading }

art { Vogue, June 1972 | Tom Wesselmann, Smoker #9, 1973 }

We suggest that advanced civilizations could cloak their presence, or deliberately broadcast it, through controlled laser emission.

Such emission could distort the apparent shape of their transit light curves with relatively little energy, due to the collimated beam and relatively infrequent nature of transits.

We estimate that humanity could cloak the Earth from Kepler-like broad-band surveys using an optical monochromatic laser array emitting a peak power of ∼30 MW for ∼10 hours per year.

{ Monthly Notices of the Royal Astronomical Society | Continue reading }

In April 2018, the servers of the popular video game “Fortnite” crashed for 24 hr. During this period, Pornhub (a popular pornographic website) analyzed trends in pornography access, finding that: (a) the percentage of gamers accessing Pornhub increased by 10% and (b) the searches of pornographic videos using the key term “Fortnite” increased by 60%.

{ Journal of Behavioral Addictions | Continue reading }

related { How Fortnite became the most important video game on the planet }

update { Online divorce service says ‘Fortnite addiction’ cited in 200 divorces }

pochoir, brush and india ink { Roy Lichtenstein, Hand Loading Gun, 1961 }

Knowing yourself requires knowing not just what you are like in general (trait self-knowledge), but also how your personality fluctuates from moment to moment (state self-knowledge). We examined this latter form of self-knowledge. […]

People had self-insight into their momentary extraversion, conscientiousness, and likely neuroticism, suggesting that people can accurately detect fluctuations in some aspects of their personality. However, the evidence for self-insight was weaker for agreeableness. This apparent self-ignorance may be partly responsible for interpersonal problems and for blind spots in trait self-knowledge.

{ PsyArXiv | Continue reading }

oil on canvas { Willem de Kooning, Untitled XXIX, 1983 }

We investigated the association between sexy-selfie prevalence and income inequality. […] Among 5,567 US cities and 1,622 US counties, areas with relatively more sexy selfies were more economically unequal. […] We investigated and confirmed that economically unequal (but not gender-oppressive) areas in the United States also had greater aggregate sales in goods and services related to female physical appearance enhancement (beauty salons and women’s clothing).

{ Proceedings of the National Academy of Sciences | Continue reading }

“Selfies” (self-taken photos) are a common self-presentation strategy on social media. This study experimentally tested whether taking and posting selfies, with and without photo-retouching, elicits changes to mood and body image among young women. […] Women who took and posted selfies to social media reported feeling more anxious, less confident, and less physically attractive afterwards compared to those in the control group. Harmful effects of selfies were found even when participants could retake and retouch their selfies.

{ Body Image | Continue reading }

When young children during their early development for the first time get their head around the fact that the reflection in the mirror is them, they are struck with a terrifying realization: All at once it dawns on them that this is how they present themselves to the world – and that the world might be repulsed by the sight. Animals, it seems, are not able to make that discovery. […] Hearing a recording of one’s own voice for the first time produces a similarly uncanny sensation.

{ Rolf Degen | Continue reading }

Two years ago a New Scientist headline announced the “world’s first baby born with new ‘3 parent’ technique.” Whereas an embryo is usually produced by one sperm and one egg, this technique uses genetic material from three separate people. First performed by a New York fertility clinic in Mexico to evade US legal restrictions, the procedure has now been replicated several times. […]

Two cases in the UK and Mexico involve a woman who carries a rare disease of her mitochondria, the cellular structures that produce energy in our cells. Mitochondria have their own DNA and can harbor their own genetic diseases. These are passed on solely through the maternal line, because mitochondria are found in eggs but not in sperm. One approach to blocking transmission of these illnesses involves inserting the DNA-filled nucleus from the egg of the woman into a donor egg full of healthy mitochondria but stripped of its own nucleus. Fertilize that hybrid egg with a sperm, and presto! A child could be born nine months later with DNA from three people and without a catastrophic mitochondrial disorder. […] Children conceived with a third person’s mitochondria are, it follows, the offspring of three parents. […]

Mitochondria, it turns out, were originally bacteria; their free-wheeling existence came to an end one day deep in evolutionary history when they entered another single-celled organism and started a new life inside. […]

This is not what we think of as Darwinian evolution, the transmission of genes and traits down the family line. DNA, it turns out, can also be passed laterally, between individuals, including those of different species. […] We may like to think of DNA as the neat bequest of our parents, the fusion of two unique, circumscribed human lineages.  Yet it is—and we are—something more: short strands within a vast interwoven genetic web, stretching back to the earth’s earliest days, linking all living things. 

{ New Republic | Continue reading }

Human memory systems are subject to many imperfections, including memory distortions and the creation of false memories. Here, we demonstrate a case where memory distortion is adaptive, increasing the overall accuracy of memories. […]

Although participants’ memories were systematically distorted, they were distorted in a way that is consistent with minimizing their average error […]

Thus, memory distortion may not always be maladaptive: in some cases, distortion can result from a memory system that optimally combines information in the service of the broader goals of the person. Furthermore, this framework for thinking about memory distortion suggests that false memory can be thought of on a continuum with true memory: the greater uncertainty participants have about an individual item memory, the more they weight their gist memory [Gist traces are fuzzy representations of a past event]; with no item information, they weight only their gist memory.

{ PsyArXiv | Continue reading }

photo { Ana Mendieta, Untitled, from Silueta Series, Iowa, 1978 }

When scientists began tracking the health of 268 Harvard sophomores in 1938 during the Great Depression, they hoped the longitudinal study would reveal clues to leading healthy and happy lives. […] They eventually expanded their research to include the men’s offspring, who now number 1,300 and are in their 50s and 60s, to find out how early-life experiences affect health and aging over time. […]

Over the years, researchers have studied the participants’ health trajectories and their broader lives, including their triumphs and failures in careers and marriage. […]

“The surprising finding is that our relationships and how happy we are in our relationships has a powerful influence on our health,” said Robert Waldinger, director of the study. […] Close relationships, more than money or fame, are what keep people happy throughout their lives, the study revealed. […] Those who kept warm relationships got to live longer and happier, said Waldinger, and the loners often died earlier. “Loneliness kills,” he said. “It’s as powerful as smoking or alcoholism.” […]

The study showed that the role of genetics and long-lived ancestors proved less important to longevity than the level of satisfaction with relationships in midlife.

{ Harvard Gazette | Continue reading }

The Grim Reaper, the personification of death, is a well known mythological and literary figure. Reported characteristics include a black cloak with cowl, a scythe, and cachexia. High quality scientific research linking the Grim Reaper to mortality has been scarce, despite extensive anecdotes.

Walking speed is a commonly used objective measure of physical capability in older people, predicting survival in several cohort studies. A recent meta-analysis found that being in the lowest fourth of walking speed compared with the highest was associated with a threefold increased risk of mortality. Moreover, the association between slow walking speed and mortality seems consistent across several ethnic groups and shows a dose-response relation. Although the association between walking speed and mortality has been well documented, the plausible biological relation between the two remains unclear.

We assessed whether the relation between slow walking speed and mortality results from the increased likelihood of being caught by Death. By assessing this relation using receiver operating characteristics curve analysis, we hypothesised we would be able to determine the walking speed of the Grim Reaper—information of importance to public health. […]

[1705] men have been followed for a mean of 59.3 months. Walking speed at baseline was not available in 77 men, mostly through inability to complete the test. A total of 266 deaths occurred during follow-up. […]

Based on receiver operating characteristics analysis and estimation of the Youden index, a walking speed of 0.82 m/s (2 miles (about 3 km) per hour) was most predictive of mortality. Therefore, we predict that this is the likely speed at which the Grim Reaper prefers to ambulate under working conditions. Older men who walked at speeds greater than 0.82 m/s were 1.23 times less likely to encounter Death. In addition, no men walking at speeds of 1.36 m/s (3 miles (about 5 km) per hour) or above were caught by Death (n=22, 1.4%). This supports our hypothesis that faster speeds are protective against mortality because fast walkers can maintain a safe distance from the Grim Reaper. Interestingly, the predicted walking speed of Death estimated in the present study is virtually identical to the gait speed (0.80 m/s) associated with median life expectancy at most ages and for both sexes in a recent meta-analysis of gait speed and mortality using data from diverse populations. This indicates that the preferred walking speed of the Grim Reaper while collecting souls is relatively constant irrespective of people’s geographical location, sex, or ethnic background.

{ British Medical Journal | PDF }

The new “eyes wide shut” illusion uses a standard enlarging (shaving or makeup) mirror. Close one eye and look at the closed eye in the mirror; the eye should take up most of the mirror. Switch eyes to see the other closed eye. Switch back-and-forth a few times, then open both eyes. You see an open eye. Which eye is it? To find out, close one eye. Whichever you close, that’s the eye you see. How can this be possible? The brain is fusing two images of the two eyes.

{ Perception | Continue reading | Thanks Brad! }

However, no one has hitherto laid down the limits to the powers of the body, that is, no one has as yet been taught by experience what the body can accomplish solely by the laws of nature, in so far as she is regarded as extension. No one hitherto has gained such an accurate knowledge of the bodily mechanism, that he can explain all its functions; nor need I call attention to the fact that many actions are observed in the lower animals, which far transcend human sagacity, and that somnambulists do many things in their sleep, which they would not venture to do when awake: these instances are enough to show, that the body can by the sole laws of its nature do many things which the mind wonders at.

Again, no one knows how or by what means the mind moves the body, nor how many various degrees of motion it can impart to the body, nor how quickly it can move it.

{ Spinoza, Ethics, III, Proposition II, Scholium | Continue reading }

unrelated { eye colour may not be a priority when choosing a partner }

The Cynical Genius Illusion

Competent individuals held contingent attitudes and endorsed cynicism only if it was warranted in a given sociocultural environment.

Less competent individuals embraced cynicism unconditionally, suggesting that — at low levels of competence — holding a cynical worldview might represent an adaptive default strategy to avoid the potential costs of falling prey to others’ cunning.

{ Personality and Social Psychology Bulletin | Continue reading }

photo { Susan Unterberg, Horse eyes #3, 1999 }

Two theoretical frameworks have been proposed to account for the representation of truth and falsity in human memory: the Cartesian model and the Spinozan model. Both models presume that during information processing a mental representation of the information is stored along with a tag indicating its truth value. However, the two models disagree on the nature of these tags. According to the Cartesian model, true information receives a “true” tag and false information receives a “false” tag. In contrast, the Spinozan model claims that only false information receives a “false” tag, whereas untagged information is automatically accepted as true. […]

The results of both experiments clearly contradict the Spinozan model but can be explained in terms of the Cartesian model.

{ Memory & Cognition | PDF }

art { Richard Long, Dusty Boots Line, The Sahara, 1988 }

In 2014, stories appeared in national and international media claiming that the condition of “selfitis” (the obsessive taking of selfies) was to be classed as a mental disorder by the American Psychiatric Association and that the condition could be borderline, acute, or chronic. However, the stories were a hoax but this did not stop empirical research being carried out into the concept. The present study empirically explored the concept and collected data on the existence of selfitis with respect to the three alleged levels (borderline, acute, and chronic) and developed the Selfitis Behavior Scale (SBS).

{ International Journal of Mental Health and Addiction | Continue reading }

photo { Francesca Woodman, Untitled, Rome, Italy, 1977–1978 }