Editor's pick: When microbes fight back
Engineering gut microbes to do our bidding is a fascinating and important research area (6 June, p 40). But bacteria have short generation times and large population sizes, and can therefore evolve quite rapidly if selection pressure is strong 鈥� as it is in the highly competitive environment of the human gut.
If we arm a particular bacterium to seek out and destroy, say, cholera, the weapons might end up being used in very different ways from those we intended. It is doubtful that our engineered bacteria would, in their original state, occupy a “fitness peak” in the evolutionary landscape of the gut; but if they evolved to kill off all their competitors, rather than just the ones we engineered them to kill, that might represent quite an attractive fitness peak and they might evolve towards it quite rapidly. Even if we engineer a “kill switch” to allow us to eliminate the bacterium if something goes wrong, the pressure to evolve a way to evade it would be immense.
I hate to quote Jeff Goldblum’s rather silly character in Jurassic Park, but when he said that “life finds a way”, he did have a bit of a point. We have learned this lesson over and over; it has had an enormous impact on our treatment of HIV and AIDS.
Ithaca, New York, US
Iron in the blood and the brain
I was interested to read Clare Wilson’s report on iron levels in the brain predicting when people will get Alzheimer’s disease (23 May, p 17). A fundamental question about iron status in the cerebrospinal fluid has not yet been addressed, however, because this study measured the amount of ferritin protein, not the amount of iron bound to it.
A review by Yunlong Tao and colleagues confirmed that iron levels increase in certain regions of the brain in Alzheimer’s disease, but also that iron in blood serum decreases (). Meanwhile, Douglas Kell and Etheresia Pretorius argue that the ferritin level in serum is an important inflammatory marker as it is mainly a leakage product from damaged cells; strikingly this serum ferritin has lost most of its iron ().
I conclude that determining whether the ferritin present in cerebrospinal fluid that predicts Alzheimer’s disease has retained or lost its iron will affect our understanding of iron regulation in disease and the scope for developing future treatment.
Coventry, West Midlands, UK
My Twitter feed is supposed to be filled with innate cruelty and savagery, not excitement and joy
tweets to plucky little Philae’s waking up (20 June, p 6)
Nature's way with energy storage
The Global Apollo Programme to persuade governments to spend a sum equivalent to the Apollo space programme on solving our energy needs is to be applauded (6 June, p 6). I do hope the programme remembers that solar energy need not be converted to electricity before it can be stored.
Nature has already cracked the problems of storing and distributing solar energy. Plants eschew mechanical and electrical methods, using biochemistry instead: photosynthesis to capture solar energy and starches and oils to store it. Distribution is then easy.
When nature does something differently to us, we may be missing something. Looked at this way, the challenge is to discover how to use plant chemistry efficiently enough to undercut fossil fuels and not starve people of food. It would be a pity to waste 拢15 billion a year for 10 years going down the wrong track.
Combe Martin, Devon, UK
What is value in a cashless society?
Jem Bendell discusses four threats looming for any cashless society (6 June, p 24). It that a cashless economy is already proposed in Israel, in the name of preventing money laundering and tax evasion.
I fear Bendell may have missed the biggest threat of all. If we live in a cashless society there will be nothing to stop the base interest rate being driven down well below zero in an attempt to “stimulate the economy”, since there will be no way for anyone to take money out of the system.
Waterlooville, Hampshire, UK
The price of paying for carbon offsets
Michael Le Page mentions carbon offsets for flying (30 May, p 37), but does not follow the logic through. In order to have money for the offsetting 鈥� and indeed the flights 鈥� one must normally earn it. Being employed is a carbon-generating process for most.
Those of us with the disposable income to fly and pay for the offset should instead be able to forgo the money and the carbon emissions by working less and pursuing low-carbon pastimes. Stay at home, and go to bed when it’s dark. In the day, read second-hand books or take walks and cycle rides.
Ringwood, Hampshire, UK
A selfishness tax on all consumption
Gail Haslam Loose suggests taxing “selfish” indulgences that harm our environment to fund mending it (Letters, 30 May). But I think she picks a strange target. The effects of a handful of space tourists’ joyrides are dwarfed by the steady accumulation of carbon dioxide from the everyday affairs of the ordinary millions, herself included. To cure this requires us to tax producers on the contamination wrought by their products, or to tax all users.
Taunton, Somerset, UK
There are more fish in some waters
The “hydra effect”, in which a higher death rate in a particular species ultimately increases the size of its population, is of great interest to those of us studying trends in the inland fisheries community (30 May, p 28). Catches have been growing steadily since records began in the 1950s, despite increasing pressure on freshwater environments.
To a certain extent this has been explained by a “fishing-down” process in multi-species fisheries, with the progressive replacement of larger species with smaller and more productive species whose evolutionary strategies include spawning many offspring.
Nevertheless, with the increased pressures one would predict a collapse at some point when fishing effort is excessive. This has happened in many single-species fisheries; but complex fisheries of tropical rivers, in particular, seem to have accommodated the extra fishing and declining quality of the environment. This is perhaps another case of the hydra effect.
Stoke by Clare, Suffolk, UK
There are more fish in some waters
Peter Abrams lists a number of negative feedbacks that put the brakes on population decline: fewer predators, less disease, more resources.
But taken at face value these are ordinary negative feedbacks 鈥� they will reduce the decline caused by, say, culling, but provide no apparent reason for a paradoxical increase in numbers. If the hydra effect is real, the explanation must be more subtle.
One complication is that, both in models and reality, a “steady state” often consists of a periodic cycle. The size of a population is interpreted as the average over the cycle. At once the paradox appears less startling: culling might lower the population in one part of the cycle while raising it in another, leading to a misleading increase in the average.
We must remember another of Abrams’s points: that culling rates only a little higher than those that maximise average population tend to lead to extinction.
Sydney, Australia
Dogs, wolves and splitting species
Michael Slezak writes that “the dates when dogs started to be domesticated and became a different species from wolves are a matter of some controversy” (30 May, p 12). Near a in Battle Ground, Indiana, there is a small rescue centre for dog/wolf crosses. These are popular pets in the US but are often too dangerous to keep.
Speciation is said to occur when lines cannot mate and produce healthy offspring, so it has obviously not occurred in the case of wolves and dogs. Comparing wolves and poodles, this is often hard to believe, but behaviour gives the game away.
Chichester, West Sussex, UK
Dogs, wolves and splitting species
鈥� The concept of “a species” is still a matter of considerable debate. Views on dogs and wolf speciation vary, depending on which aspects researchers prioritise. Canid specialists do not expect an agreed answer any time soon.
Did I train my colour vision?
The article on improving vision (23 May, p 33) reminded me of spending two years in my early 20s matching colours in a laboratory. At the medical before my next job, to doctors’ surprise I could read both the numbers I should be able to see in the Ishihara colour vision test and the numbers I should not. I put this down to the two years that I spent looking intently for differences in colours.
Bristol, UK
Alright on the night without the fright?
So machines are in training to be concert virtuosos (30 May, p 21). As an amateur violinist who once worked for a software company that published a music sequencer program, I hope someone writes performance anxiety and the urge to impress into the algorithm.
These emotions, I find, can always give performances an extra human edge.
Canonbie, Dumfriesshire, UK
Vintage vinegar sought in vain
You say that the grape juice in the 170-year-old champagne found in the Baltic Sea had not turned to acetic acid probably because of the cool temperatures and dark environment (25 April, p 20).
The reason the champagne had not turned to vinegar was that there was not enough oxygen. Every gram of acetic acid requires about half a gram of oxygen.
Les Essarts-le-Roi, France
<b>For the record</b>
鈥� We aimed for a star, but missed: the variable star photographed by the Hubble telescope is V838 Monocerotis (25 April, p 26).
鈥� We were away with the fairy circles in the deserts of Namibia, which in fact receive 50 to 100 millimetres of rain per year (13 June, p 38).