Editor's pick: Flies' visual filters may explain zebra stripes
Reviewing Tim Caro's book Zebra stripes, Matthew Cobb says that “for reasons that are still unclear, flies dislike landing on striped surfaces” (18 March, p 42). He notes the conjecture that flies cannot see stripes of some widths.
Could the reason instead be the Reichardt-Hassenstein filters that all sighted animals have in our vision neurology? These detect visual flow. You can feel them working if you walk fast down the middle of a corridor (which will feel comfortable) and then do the same close to one wall. Your filters detect the difference between the fast visual flow of the close wall and the slow flow of the far one, making you instinctively want to equalise them to minimise the danger of collision.
The filters give a strong visual flow signal for movement at right angles to stripes, and a weak one for parallel movement. This gives conflicting information about how fast a fly is approaching a striped surface, which would make landing difficult. Hence, maybe, the evolution of zebras' stripes.
Another reason for the brain's border control
James Mitchell Crow discusses the blood-brain barrier (18 March, p 34). But he doesn't mention an important reason for limiting the entry of inflammatory cells and cytokines to the brain.
The brain is the only organ (unless you count bone marrow) encased in a rigid container. It has just one significant exit, the foramen magnum at the base of the skull.
Expansion of the brain, such as that associated with haemorrhage, inflammation or injury, can only occur here, which compresses the hindbrain. This process is called coning and is rapidly fatal unless treated. Organisms with brains not protected from the usual processes of inflammation are less likely to survive, compared with those with an efficient blood-brain barrier. I fear it may be dangerous and counter-productive to interfere with this barrier therapeutically.
How safe are tobacco pouch products?
I am amazed that you didn’t mention the risks of tobacco products such as snus (18 March, p 6). I seem to remember reading over the years about them causing cancers. Has something changed?
How safe are tobacco pouch products?
You report smoking rates for men in their 30s in Sweden plunging to 5 per cent. As you say, this is likely linked to 18 per cent of Swedish men using snus as a smoking substitute. But is snus safe?
The World Health Organization says that it is “considerably less hazardous” than smoking. The EU says the relative health advantages are “undeniable”. In the longer online version of the article you quote a Cancer Research UK official singling out pancreatic cancer as a concern. Swedish men have the lowest rate of pancreatic cancer in the EU. Swedish Match is happy to provide public health bodies with independent scientific evidence.
Could smoking reduction have other causes?
You say that plain packets help Australian smokers quit (4 March, p 6). But couldn't the decrease in Australian smokers after the advent of plain packaging be caused by other facets of an anti-smoking campaign?
It may be a “record decline”, but is it dramatically different from the decrease in smoking since the anti-smoking campaign began?
The editor writes:
• Several readers asked similar questions. The introduction of plain packaging coincided with an abrupt steepening in the trend line for declining smoking rates.
The carbon emissions from building islands
Does anyone else see an irony in the Maldives building up islands or constructing new ones as sea levels rise (25 March, p 12)? The energy used will release more carbon dioxide, as will the planes bringing in tourists, with their own enormous footprints.
This is a microcosm of the spiral of hedonistic lifestyle we have got ourselves into ever since we started on the industrial bandwagon.
It's time for a big – global – cost-benefit analysis of what we are expecting to take from the environment and what we put out. It may already be too late, but we must continue to try.
Are emotions a palette built from primaries?
Lisa Feldman Barrett argues that the way our brain interprets any single emotion is culture-dependent and we “rewire” our brain to conceptualise different emotions (11 March, p 40). Whenever the article mentions one of these “new” emotions, they are always explained as a combination of others.
For example, the Japanese arigata-meiwaku is the negative feeling when someone does you a favour that you didn't want.
I wonder whether there is in fact a set of “primary” emotions which, like primary tastes, forms a basis on which cultural concepts of emotions build.
Lisa Feldman Barrett writes:
• One version of the classical view does propose that a small set of emotions are “basic” and universal. But research shows that people in different cultures have different emotions that feel to them like “primaries”. For example, in situations where a Westerner might feel sad, Tahitians feel an emotion called pe'ape'a which is more similar to “ill” or “fatigued”.
We define dimensions because they are useful
Stuart Clark asks whether there are really just three dimensions (4 March, p 31).
Weren't the three dimensions created by us as a convenient mathematical way to understand and measure spaces and to plan and construct things?
Shouldn't the question be “Can we better understand, measure, model and make things by using a mathematical method that has more dimensions than the traditional three?”
Life in a universe with an infinite speed of light
Stuart Clark suggests that, if the speed of light were infinite, “cause would sit on top of effect and everything would happen at once” (4 March, p 29). But would all physical movement, nuclear reactions and biological evolution become instant?
Wouldn't a major effect be to provide the universe with an absolute time, uniform for all frames of reference everywhere?
Albert Einstein's argument against simultaneity would fail, since we could then ascertain whether any two events anywhere were simultaneous by simple observation.
Time would just rumble on, a constant framework for the other main forces of nature.
Life in a universe with an infinite speed of light
Clark mentions the experiment by US physicists Albert Michelson and Edward Morley that tried to measure the then-expected difference in the speed of light in “the direction of Earth's rotation” and at right angles to it.
It's worth recalling that this difference was expected to be caused primarily by Earth's rotation around the sun (with a velocity of 110,000 kilometres per hour) not that on its axis (1700 kilometres per hour).
Modifications to what kind of gravity?
Mark Anderson (7 January, p 9) tells us that Erik Verlinde's new theory of gravity builds on Mordehai Milgrom's modified Newtonian dynamics (MOND) theory. But does the new theory still support space-time in which gravity is linked to the curvature of space? Does it have time dilation and does it explain the precession of Mercury? In other words, is it rather a Modified Einsteinian Dynamics?
All medical data must be kept secure
In your report on the roll-out of two apps that help people monitor their health at home by UK National Health Service trusts, I didn't see any mention of data security (18 February, p 11).
Have any of these apps been independently security audited? Apart from the dangers of personal data theft, subverting them to mislead healthcare professionals could cause real harm to patients by misdiagnosis.
These apps are being used for diagnosis, so they should be formally approved under the EU medical device directives.
Another reason not to give up bread for Lent
The information in 快猫短视频 comes to my rescue again. I had been thinking of decreasing my carbon dioxide emissions in Lent by switching to unleavened bread and eliminating the generation of yeasty gases. However, since “the equivalent of half a kilogram of carbon dioxide goes into the atmosphere for every loaf” (4 March, p 14), it seems my sacrifice would only be symbolic.
End of an era
F. White suggests we should leave the naming of the new geological period to whoever inhabits it (Letters 18 March). I have thought for many years that we humans are presently living in the Endoscene period.
For the record
• Thar she blew. The early 1900s was when blue whale numbers crashed because of factory-ship whaling (18 March, p 44).
• The tectonic plates of Europe and North America are separating (UK and Australian editions, 18 March, p 51).