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Michael Marshall's fascinating article on the first 3.5 billion years of life on Earth reinforces how fleeting human history is when placed in the context of such a vast period ( 12 January, p 28 ). A fantastic way to convey this point would be to represent the history of life along a walk in …

It should show the pain it feels and bite the person who kicked it Evelyn delves into ethics on reading of a dog-like robot that learned to get up when kicked over ( 26 January, p 12 )

Some health campaigners may have welcomed the launch of the UK government's 10-year plan for the National Health Service (NHS) in England ( 12 January, p 6 ). But, for example, Youssef El-Gingihy, a doctor in east London and author of How to Dismantle the NHS in 10 Easy Steps , notes that the form …

Chris Baraniuk attributes the extinction of cave bears to an inability to cope with the last glaciation ( 22/29 December 2018, p 60 ). But the species made it through the more severe Anglian glaciation around 450,000 years ago. Many climatic explanations of extinctions look at the period of demise in isolation without explaining why …

After my regular 30-minute stumble around the local cemetery, I read with interest that I can't just burn off extra calories ( 19 January, p 30 ). Admittedly, I exercise for the endorphin kick and because it makes me laugh. But when I was gardening for 4 to 12 hours a day, I could eat …

Graham Lawton discusses how to organise your day ( 12 January, p 34 ). I nonetheless found myself wondering to what proportion of the working population his remarks had any relevance. I thought of production line workers required to sustain a constant input from clocking in to clocking off. I thought of teachers, who need …

Leah Crane tells us that batteries on the New Horizons spacecraft can power the equivalent of three standard light bulbs ( 5 January, p 7 ). What is a "standard light bulb"? Once upon a time, I might have imagined a 60-watt filament bulb, but they are obsolete. It would make more sense to say …

Stuart Leslie suggests that the oldest figurative art in the world produced by Homo sapiens may occur in Australia (Letters, 5 January ). He says that some depicts the giant flightless bird Genyornis newtoni and that this appears to have become extinct around 46,000 years ago. But the rock images that were proposed, on the …

You report that there may be an intermediate-mass black hole the size of Jupiter in our galaxy ( 19 January, p 14 ). Wouldn't one of these have significantly greater mass than the planet? The editor writes: • The diameter of the event horizon of the suggested black hole would be roughly Jupiter's diameter. The …

Jim Skeels suggests that neural activity could perhaps be recorded closer to the source through a dental implant, which may also be less obtrusive than a full EEG cap on the skull (Letters, 1 December 2018 ). This is an interesting idea, but a midline slice of the skull shows that a tooth implant would …