Category Archives: nature

high blood pressure affects colour vision


Drinking alcohol not only affects your speech and balance. It can also affect your colour vision. Not just alcohol. Various drugs (some contraceptives and analgesics, for example) make you less good at discriminating between colours. And there are a load of medical conditions that also affect your colour vision including MS and diabetes. In fact, often a deterioration in colour vision can be one of the first indications of a problem. This is why it is a good idea, from a health perspective, to have your vision checked by a qualified professional on a regular basis.

Now some research from Japan suggests that deterioration in colour vision may be a predictor of hypertension – a condition in which the arteries have persistently elevated blood pressure. The study looked at 872 men aged between 20 and 60. They found that, when other factors were taken into account, as blood pressure values rose, the odds of having impaired colour vision increased as well.

For further information see here.

why do we value gold?


Could we have developed currency around elements other than gold and silver? Why couldn’t we have coins made out of platinum, for example?

Interesting article today on the BBC website interviewing Professor Sella (University Collage London) about why, of the 118 elements of the periodic table, it is gold (alongside silver) that we value and use for currency.

According to Prof Sella there are reasons to dismiss all the elements apart from gold and silver. For example, you couldn’t use elements that are gas (such as neon) or liquid (mercury) as currency because it would be impractical to carry them around. Several others (such as arsenic and the other liquid, bromine) are poisonous and so could not be practically used. The alkaline metals (those on the left-hand side of the periodic table) are not stable enough (they react with too many other elements). And, of course, say no more about the radioactive elements. Some of the so-called rare earths (such as cerium) could be used but they tend to be even more rare that gold and are actually quite difficult to distinguish from each other.


Prof Sella also postulates reasons for dismissing the 40 transition and post-transition elements such as copper, lead, iron and aluminium. Many are hard to smelt (needing temperatures as high as 1000 deg C) such as titanium and zirconium or hard to extract such as aluminium. Iron is easier to extract and smelt but rusts too easily. Iron is also too abundant.

Prof Sella lists the 8 noble metals (platinum, palladium, rhodium, iridium, osmium and ruthenium, gold and silver) as contenders. However, with the exception of silver and gold they are too rare and have other problems (platinum is hard to extract and has a very high melting point for example). So this leaves gold and silver. The choice of these metals is not arbitrary. It turns out that they have exactly the right properties that we need. They are stable, chemically uninteresting, rare (but not too rare), safe, relatively easy to extract, solid at room temperature and with a reasonably low melting temperature.

The article also explains why gold is golden in colour.

I like my carrots black


On Christmas day of 2009 I posted about the colour of carrots.

I had been watching a Royal Institution Christmas Lecture by Prof Sue Hartley about carrots and why they are orange. She spoke about selective breeding by the Dutch (the first naturally occurring carrots were purple – from Afghanistan – and were later cultivated to be orange). In seeking to find more about this I found myself on the website of the British Carrot Museum. It is seriously worth a visit even if your interest in carrots is tangential.

I was reminded of this today when I came across an article in The Economic Times (India) which reported that the Punjab Agriculture University has developed its first black colour carrot variety (known as ‘punjab black beauty’) which has been recommended for general cultivation in the state. The black carrot is the best alternative to tackle the malnutrition problems of the country because it is overloaded with beneficial anti-oxidants and nutrients. The punjab black beauty is is rich in anthocyanins, phenols, flavonols ß-carotene, calcium, iron, and zinc.

I am also reminded, of course, of the words of the great late Uncle Monty (aka Richard Griffiths): “I think the carrot infinitely more fascinating than the geranium. The carrot has mystery. Flowers are essentially tarts. Prostitutes for the bees. There is a certain je ne sais quoi – oh, so very special – about a firm, young carrot”.

Eat red, eat less


It used to be thought that blue was an appetite suppressant because blue foods are rare and sometimes poisonous. But I have always doubted this and wrote about it near three years ago on this blog. And then nearly two years ago I posted about research from the University of Basel (Switzerland) and the University of Mannheim (Germany) in which it was shown that participants drank less from a red cup than a blue cup and ate less snack food from a red plate than from a blue plate. In other words, the opposite of what was commonly believed. Today I read in CNN about work by Nicola Bruno, a cognitive psychologist from the University of Parma, about his research to measure how much food or hand cream people used when presented on plates of different colours (red, white or blue). The food and hand cream was available to be used freely whilst participants took part in a survey. People ate less food and used less hand cream when either was presented on a red plate. However, the authors note that in their experiment the participants were unaware of the experiment – so it is not so straight forward to extrapolate and conclude that if you buy red plates for home you would eat less. Because then you would be conscious of the idea and it might not work. On the other hand, it might!!

It was nice for me to hear this story and it reminded me of when Nicola came to visit me (when I worked at Keele University) and we published a paper together. That was in about 2000 and I don’t think I have seen him since. Sometimes it isn’t a small world. But it was nice to come across him again anyway.

dog vision

I just read an article in The Daily Mail that says that most people think dogs do not have colour vision. The article then goes on to say that Russian scientists have proved that dogs do have colour vision. It seems to me quite accepted that dogs are dichromats – that is they have two types of light-sensitive cells that contribute to colour vision in their eyes. We – humans – are trichromats because we have three such cells. It turns out that the one that is missing – in dogs – is such that dogs’ colour vision is rather like that of a human who has red-green colour blindness. The image below shows how the spectrum looks to a trichromatic human and a dichromatic dog.


As you can see, dogs can bee blues and yellow but have difficulty discriminating between colours in the red-green part of the spectrum. So I am not sure what the fuss is about with the Daily Mail article. After all, everything in the Daily Mail is true!! See if you don’t believe me.

eyes change colour?


I didn’t realise how sophisticated reindeers are. It turns out they have two layers of fur to help them keep warm, are able to shrink the pads on their hooves to give then better grip, and can detect ultraviolet light which enables them too see in very dim light. And it also turns out that their eyes can change colour in winter so that their vision is more sensitive. Reindeers, like cats, have a reflective layer behind the retina (which is the inside of the eye ball where all the light-sensitive cells are) that helps them to see in dim light. This is why, if you see a cat at night, you might see the eyes shining; you are seeing light being reflected back at you from the cat’s tapetum lucidum (which is the technical term for the layer behind the retina). The light that shines back in most animals with this layer is golden but in reindeer it apparently shifts to blue in the winter. The shift to blue allows more light to be scattered and improves the vision of the animal.

The full paper can be read in the Proceedings of the Royal Society.

skin colour and personality

Excellent article based on an extract from Nina Jablonski’s book “Living Colour: The Biological and Social Meaning of Skin Colour” about early ideas about the relationship between skin colour and personality.

The first scientific classification of humans, published by Carl Linnaeus in 1735, was simple and separated people into four varieties by skin colour and continent. Later, Linnaeus added that Europeans were white and “sanguine,” Asians were brown and “melancholic,” Native Americans were red and “choleric” and Africans were black and “phlegmatic”. Of course, these racist pronouncements were based on prejudice and myth and little, if any, factual information. Nevertheless, these ideas led to an intellectual foundation for racism. Immanuel Kant, was the first to formally define races and in 1785 classified people into four fixed races, which were arrayed in a hierarchy according to colour and talent. It sounds like a really interesting book on anthropology and I’ll order a copy tomorrow. I’ll try to remember to comment when I have read the full book.

Four temperaments is a proto-psychological interpretation of the ancient medical concept of humorism and suggests that four bodily fluids affect human personality traits and behaviors. The temperaments are sanguine (pleasure-seeking and sociable), choleric (ambitious and leader-like), melancholic (introverted and thoughtful), and phlegmatic (relaxed and quiet).

Eye colour and trust

According to a recent study eye colour plays a role in deciding how trustworthy others will think you are. Researchers simply asked a group of people to rate the trustworthiness of male and female faces. It was found that a majority of people found people with brown eyes to appear more trustworthy. This was true for both sexes but particularly so for men.


But it turns out that it is face shape that is more important and eye colour is a major factor because brown-eyed people tend to have certain facial characteristics. For the original story see here.

chicken colour vision

Most humans are trichromatic; that is, our colour vision is mediated by three types of light receptor in our eyes. These receptors are known as cones and the three types have peak sensitivity in different parts of the colour spectrum. We sometimes refer to these as LMS cones because of their peak sensitivity at long-, medium- and short-wavelengths light.

Some people (men, in the main) are colour blind and this is because they are anomalous trichromats (they have three cones but the spectral sensitivities are less optimal than they should be or they are dichromats (they are missing the L, M or S cone types). But what about other species?

Most mammals are dichromats including dogs and cats. However, many fish and birds have better colour vision than do we humans. I just came across an article that reports that chicknes have five cones compared with our three. The research has been conducted the Washington University School of Medicine in St. Louis (USA). It is suggested that birds often have more cones than we do because they descended directly from dinosaurs and never spent any part of their evolutionary past living in the dark.

special females

Our colour vision results from the fact that our eyes contain three types of light-sensitive cells or cones that have different wavelength sensitivity. Some people (called anomalous trichromats) are colour blind and this is usually because one of their cones is mutated and has a different wavelength sensitivity compared with those in so-called normal observers. Colour-blind is a misnomer really because anomalous trichromats can still see colour; they just have less ability to discriminate between colours than normals. Some people are missing one of the cone classes altogether and are referred to as dichromats; they have even poorer colour discrimination but can still see colour. Only monochromats are really colour blind and they are extremely rare.

For a long time I have known that some females have four cones classes (this makes them tetrachromats). Dr Gabriele Jordan, a researcher at the Institute of Neuroscience (Newcastle University) has spent the last 20 years working on human colour vision. She has discovered that tetrachromatic females exist and that although this gives them the potential for colour discrimination much better than normal trichromats in practice most have normal colour discrimination. However, in a recent report she has found a tetrachromat who really does have enhanced colour discrimination. This is really exciting news!

The report in the Daily Mail suggest that a functional tetrachromat could be able to see 99 million more hues than the average person. Personally I am skeptical of this claim even if, as I suspect, it means 99 million more hues than the average person. The number of colours that an average person can see is debatable but I think may be about 10 million (see my previous blog post).