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You report artificial intelligence's ability to predict dangerous tipping points in complex systems, such as stock markets. Will it predict and tell us when it is going to take over and unleash our own weapons on us, or create new viruses leading to the extinction of most human life( 3 August, p 18 )?

When it comes to ice melt changing currents in the Atlantic Ocean that help keep northern Europe relatively mild, there is another factor at work beyond rising temperatures. Wildfires in North America are burning at ever-increasing rates. Much of the ash and soot is deposited on the Greenland ice sheet, changing its albedo and vastly …

It seems premature to say that the downsides of anti-ageing therapies are a price worth paying. If they include a population explosion that turns out to be the last straw for an already overburdened planet, I suspect that the people alive at that time would disagree ( Leader, 6 July ).

Christa Lesté-Lasserre discusses the furore over a horse being whipped while training for dressage events, but doesn't address the major concern: why make a horse dance to order? If animals are unwelcome in circuses, why make a horse dance carrying a rider and call it a sport? Why "train" a horse to jump a very …

You report on a proposal to put a frozen backup of Earth's life on the moon. The idea of off-planet reserves for life, albeit not frozen, isn't new. In the 1972 movie Silent Running , forests are kept in giant greenhouses beyond the orbit of Saturn. In any event, any lunar repository could be financed …

Alex Wilkins reports that a slight curve on the surface of a rock helps it make the biggest splash. I am of a generation that received corporal punishment. It was well known that the more charitable disciplinarians used an absolutely flat instrument. We, the recipients, could feel the reason suggested in the research: the flat …

With reference to childhood exercise, an additional factor struck me. As a child in a car-less household, I was frequently presented with a purse and a shopping bag and told to run and fetch whatever was needed from the local shops, thus clocking up both aerobic and weight-bearing benefits. My own children, however, just pop …

You report that butchered bones hint at earlier human arrival in South America. But could the butchered glyptodont, which has been dated to the last glacial maximum period, have become frozen after death, like a Siberian mammoth, and likewise thawed thousands of years later and been butchered then( 27 July, p 18 )?

You speak of doping in sports as an unfair advantage. I agree. But a few pages later in the same issue ( p 11 ) you report that a Google AI has achieved a silver medal score in a human mathematics competition ( Leader, 3 August ). Considering that a computer uses much more energy …

As a bit of a poet and a bit of a mathematician (and no great shakes at either), I found Peter Rowlett's piece on mathematics and rhyme entertaining, especially the notion of the pi-ku, a haiku variant with syllables based on 3.14 for its three lines, i.e. 3, 1 and 4. Why stop there, when …