Editor's pick – Can we model decision-making in single cells?
Speaking to Richard Webb, Sean Carroll wonders whether bacteria have decision-making power or agency (15 February, p 34). Arguably, the earliest known “decision-making” in the burgeoning tree of life occurs with chemotaxis: single-celled life forms propelling themselves in response to a chemical stimulus, for example towards sources of nutrients.
Webb later quotes researcher Larissa Albantakis, who argues that the apparently deliberative quality of our agency sets it apart from this: it “is not just reflexes”. But bacterial chemotaxis is more than a single reflex action. It is a response to an environment that results in the selection, over alternatives, of one near-optimum direction to move in.
Information scientist Susanne Still says that agents follow rules that must fulfil certain criteria, including some element of memory storage and recall. Evolutionary processes constitute a memory function and provide this feedback, but over generations rather than within an individual cell.
So could focusing on a primitive form of agency 鈥� the ability to select one optimal direction from many 鈥� in a system as simple as a single cell help determine whether agency can, in principle, be explained in purely physico-chemical terms?
How can evolution happen without external reality?
Your collection of articles on reality was informative (1 February, p 39). Most provocative was Alison George reporting Donald Hoffman’s claim that nothing we perceive resembles reality and we are “born with a virtual reality headset on”. He says evolution gave us this to simplify things so we had “what we need to play the game of life”, and that what we perceive is an abstract data structure that represents something that “doesn’t even exist in space and time”. The implication that evolution therefore doesn’t occur in space and time creates problems for me. Hoffman goes on to say that evolution has shaped us to see things that we have to take seriously, to see what we need to stay alive, but that “does not, logically, permit us to say that we’re seeing the truth”.
But evolution occurs by natural selection, which requires an environment for biological agents to interact with. Assuming that we are born with such a VR headset, the “data structure” it creates must surely closely resemble the external environment it interacts with in space and time 鈥� otherwise we wouldn’t survive.
The importance of naming our parts correctly
Clare Wilson says that educating people about sexual health is more important than policing their language to prevent them referring to the vulva as the vagina (11 January, p 30). Yet that is akin to calling the lips the throat.
Such errors can lead to serious misunderstandings. One of my patients was convinced he had rectal cancer. In reality, he had a skin cancer just outside his anus. I couldn’t convince him otherwise.
Fictitious women are more equal on Wikipedia
I am amazed that some Wikipedia editors deem female scientists to be “not notable enough for inclusion” (8 February, p 46). Many characters from anime films have their own pages, even supporting characters.
The meaning of life is simpler than it seems
People are intrigued by the Canadian frogs that freeze in winter and thaw out in summer (Letters, 11 January). Are they alive or not? It sounds like a deep philosophical question, but it isn’t.
“Life” is a collective noun for things that are living. Things transition from being dead to alive all the time. Every time you breathe in, atoms that were dead are incorporated in your body and begin to live. When you breathe out, atoms that were living are sent into the atmosphere and are now dead. Life isn’t a substance: it is an activity.
So are the frozen frogs active? No. Therefore they aren’t living. When you thaw them out, are they active? Yes, so they are living. As every detective story teaches you, it is the time of death that is important. Whether something is alive or not can only be answered with reference to a time. This is the meaning of “life”.
Don't forget the role of the body's thermostat
Average human body temperature has fallen in the US since the 1860s, reports Michael Marshall (18 January, p 13). Julie Parsonnet, one of the team that analysed data from more than 677,000 measurements, says the most likely explanation is that immune systems have become less active because we get fewer infections, leading to a reduction in inflammation and therefore heat production.
This seems unlikely to be the explanation. The body’s heat production very much depends on physical activity, which varies enormously from moment to moment in individuals and also from person to person.
Body temperature is far steadier, being mainly controlled by the brain’s hypothalamus, which acts somewhat like the thermostat of a central-heating system. The doesn’t mention this.
A more likely explanation of the gradual temperature fall lies in a steady change in the average setting of the thermostat. This is raised to higher temperatures during fever.
Two further, and in some sense opposing, considerations are that ill people are often less active, which would imply that the reduction in infection means more heat production, and that work has tended to become more sedentary over the years, which implies less heat production.
This military invention is music to my ears
You report that arm heaters that keep hands warm without gloves are being developed by the US Army (18 January, p 14). Let me assure the researchers that there is a large non-military community to whom this invention would be of incalculable benefit: musicians.
At any outdoor gig in cool weather 鈥� or even in TV studios that keep the temperature low 鈥� one sees multiple hand-warming devices and much rubbing and blowing of hands among the band or orchestra.
I don’t know of a single colleague who wouldn’t welcome the proposed arm-warming device with great enthusiasm. You quote a reduction of dexterity loss by 50 per cent and of finger-strength loss by 90 per cent in those wearing it. Whatever instrument one plays, that would make a gigantic difference to the performer and thus to the quality of the music.
Beware the consequences of these good intentions
Alain William proposes a unit of environmental impact, the Thunberg (Letters, 1 February). Though designed to achieve desirable outcomes, this seems to have much of the charm of China’s Social Credit System (17 October 2015, p 22).
Likewise, Stewart Reddaway suggests that passenger aircraft should limit the number of premium seats (also in Letters, 1 February). This measure to achieve an environmental goal could also lead us to a dystopia in which, among other things, environmental problems would be impossible to solve. In this case, ask yourself a simple question: who gets the few remaining premium seats?
Science denial tactics are on a hiding to nothing
Michael Marshall reports on fears that a conference on scientific reproducibility has a hidden agenda to create doubt about climate change and hence support the fossil fuel industry (1 February, p 11). If so, its organisers are fighting a rearguard action to try to delay their retreat.
Wind and solar is now less expensive than coal. Add the economic success of the Australian mega-battery (15 July 2017, p 6), which I understand was on track to produce revenue equal to almost a third of its capital costs after a year of operation, and the writing is on the wall.
Economics is a more powerful motivator than street protests and outraged articles. The icing on the cake is that when you install a tranche of solar panels or wind turbines, it immediately goes into operation, providing revenue to fund the next installation. A coal-powered generator, in contrast, has to be completed before producing any revenue.
Do trees feed bacteria that make rain fall?
Fred Pearce says large areas of tropical forest promote more rainfall than previously thought (2 November 2019, p 40). I recall that clouds contain tiny organisms. Trees emit complex chemicals 鈥� could these be the feedstock for aerial bacteria?
It might be that what the trees emit not only feeds such bacteria, but stimulates them to help provoke rainfall. Cloud seeding with aircraft to produce rain has had limited success, but bacteria and the trees that may feed them would have had many millions of years to improve the process. I wonder how far the links go and how sophisticated they are 鈥� and whether we can imitate the processes to relieve drought.
Papuan peoples could have sailed to Australia
There is obviously some question about how the earliest settlers crossed seaways en route to northern Australia (25 January, p 38). In the 1950s, I was a surveyor in Papua. Coastal peoples there made large dugout canoes and joined three of them together to form well before European settlement.
These canoes were dug out using stone axes and adzes. They had V-shaped sails woven from local materials. They couldn’t tack, but sailed well before the wind. Crossing the Gulf of Papua with this method would have been relatively easy, provided you picked the right season.
There is no reason why people 50,000 or more years ago couldn’t have built similar craft and easily travelled in a westerly direction.
We need dark matter and energy, whatever they are
Paul Leek says dark matter and dark energy are “imaginary constructs” and links them with the big bang theory (Letters, 8 February).
It is my understanding that dark matter is postulated because galaxies are observed to be spinning too fast for the gravity of the observable matter, as required by Einstein’s theory of general relativity, to hold galaxies together.
This has little to do with big bang theory. Galaxies do exist, so dark matter must exist, unless Einstein was wrong.
Dark energy is put forward to explain why the observed expansion of the universe is accelerating, when general relativity would expect it to be decelerating. Big bang theory is irrelevant.
For the record 鈥� 7 March 2020
鈥� The chart in the online version of our article on stress shows that people experienced over their lifetimes (bit.ly/NS-stress).
鈥� None of the substances found in commercial xylene is especially toxic, but they may be precursors of toxic chemicals (25 January, p 11).