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You frequently discuss humans interbreeding with Neanderthals and Denisovans (for example 22/29 December 2018, p 35 ). Presumably this was going on further back in the lineages. All these species have 23 pairs of chromosomes; other great apes have 24. Each of one certain pair of our chromosomes consists of two ancestral units stuck end …

I was fascinated by your account of fetal sharks observed by ultrasound to be swimming around in their mothers' uteruses ( 12 January, p 8 ). Adriano Milani Comparetti , a pioneer of paediatric neurology , was also interested in observing fetal movement using ultrasound. He would have raised his eyebrows at the article's description …

Your workplace survival guide was far too easy on open plan offices ( 12 January, p 33 ). Employees hate them. Even "good" examples are anathema to people who have to do work that requires sustained thinking without interruption. Their use may be legitimate in start-ups with few staff creating something new on the fly. …

A common thread runs through several of your recommendations on surviving the modern workplace . The one factor that correlates most consistently with happy and productive workers is giving them choice. One of the most effective changes that an employer can make is to give employees more control over their environment and workspace, and discretion …

Zunum Aero hopes its planned hybrid aircraft – partially powered by electricity – will manage 1100 kilometres on a single charge ( 5 January, p 32 ). You provide maps showing some of the journeys that could be accomplished. Most can be done by train. A French TGV train has achieved 574 kilometres per hour …

I understand that the section of a flight that uses most energy is take-off. Would the range of an electric plane be significantly extended by a separate external launcher, similar to those used on aircraft carriers, to accelerate it up to take-off speed?

Paul Marks envisages a future in which aircraft use biofuels or derive electrical energy from renewables. It is a pity that he didn't go more deeply into the numbers, which make this seem unlikely. In 2017, for example, worldwide commercial aviation used about 400 million cubic metres of fuel. A square kilometre of oilseed rape, …

I agree completely with Mini Grey's call for a carbon tax and dividend (Letters, 5 January ). I also share the pessimism of the letter from Blaise Bullimore that precedes it. Consider the consequences of French president Emmanuel Macron's attempt to raise extra funds for alternative energy sources by placing a small extra levy on …

Feedback refers to penguins being priced, for some obscure reason connected with valuing wasted water, at 8.8p ( 22/29 December 2018 ). This seems rather cheap. I helped manage the Phillip Island tourist destination in Australia. The tourism value of the crowd-pleasing parade of penguins that emerges from the sea each night, was about A$10,000 …

Alice Klein says that in Australia one in 20 people carries the genes for cystic fibrosis or for spinal muscular atrophy and one in 40 of those people has a partner who is also a carrier ( 22/29 December 2018, p 32 ). Those who are aware of being carriers may avoid having children with …