91É«ÇéƬ

Erle Ellis says formal recognition of an Anthropocene Epoch beginning in 1950 would be damaging in that it denies earlier human impacts. It does no such thing. Such impacts – from hunting, farming and urbanisation – go back through and characterise the 11,700 years of the Holocene (and some into earlier times). But they didn't …

Glenda Dixon asked: "Why not use thermodynamic systems to get heat from the seas to generate electricity and heat local homes?" One reason is that the devices needed would be huge because their efficiency is low ( Letters, 26 August ). The only example that ever worked for any length of time was built by …

It has been suggested that the elongated interstellar object 'Oumuamua was sent to our solar system by advanced alien life ( 2 September, p 29 ). However, natural explanations seem more likely. Lava solidifying in a volcano conduit often takes up a rod-like 'Oumuamua shape. Erosion of the surrounding rock leaves the frozen lava as …

Why is it so hard to define what is meant by ultra-processed foods (UPFs)? These comprise any edible substance made using ingredients not used by (or available to) home cooks, processed by methods not possible in home kitchens, or both of these ( 19 August, p 16 ). Incidentally, yogurt that is made in the …

I share Clare Wilson's scepticism of complementary medicine, "superfoods" and magical thinking, but the World 91É«ÇéƬ Organization (WHO) summit on alternative therapies was justified. Two of Western medicine's most important therapies, vaccines and analgesics , were first discovered by traditional healers. We shouldn't pre-emptively reject these treatments, even if most of them lack efficacy ( …

With rivers polluted by sewage, frequent drought amid climate change, associated fish deaths, organic waste and low oxygen levels all adding to the woes facing UK rivers and other water bodies, natural measures to address the worst impacts are surely going to become of increasing importance ( 12 August, p 36 ). The argument for …

A study suggests fruit flies may prefer to sit on a rotating carousel for pure enjoyment. It could be argued that flying barrel rolls and loops would be more entertaining, if fruit flies like to have fun. Isn't it more likely that the flies choose the carousel for other reasons? For example, it might be …

Annalee Newitz, who has had covid-19, says that US doctors are "leery of prescribing . No one is quite sure why." Perhaps the doctors have prior experience of this antiviral? It seems that it is effective at relieving symptoms and possibly in controlling infectivity, but there have been some reports of the virus rebounding after …

From Letters, 26 August

As the years go by, it is increasingly apparent that nuclear fusion may, one distant day, become a reality, but that it is most unlikely to be a significant player in resolving our immediate climate woes. The root problem, I believe, is that everyone expects every joule of energy we currently consume from fossil fuels …