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From From Malcolm Moore, Rotorua, New Zealand When it comes to the rise of burial practices, the basic needs for species are survival and reproduction. That means food, shelter and security. Dead bodies attract scavengers. For a vulnerable hominin species like Homo naledi who, for a period at least, stayed in one place, decaying bodies …

Seems to me that the custom of burial would have been more practical than anything else. After all, dead bodies lying about would have smelled pretty bad after a while and attracted wildlife.

When it comes to body clocks, researchers should investigate the phenomenon of "second sleep", or biphasic sleep. This is fairly well-known historically and among some anthropologists. It seems to have been relatively common and widespread at a time when people's daily rhythms were largely determined by the sun and when bright indoor lighting was unavailable …

I find the claims of species de-extinction by Colossal Biosciences unconvincing, its reasons for doing it unclear for the species it is trying to resurrect, and the prospect of the development of artificial wombs a potential horror story( 19 July, p 32 ).

I've had myalgic encephalomyelitis for 26 years, so what wonderful news to hear that there might be a way to confirm it genetically. Hopefully, funding will allow further research into this( 16 August, p 10 ).

Charlie Wartnaby, Cambridge, UK So I missed my opportunity to play geologist by "discovering" the weird anthropoclastic rock formed from industrial waste on the beach near Workington, Cumbria, UK. It seemed like an impossible kind of volcanic sandstone when we found the same thing on the north side of the town. It did indeed feel …

In connection with matrilineal societies, I saw an interesting variant in Vanuatu. Basically, young men and women relate to their mother and her siblings. You might think this would lead to some sort of matriarchy, but that appears not to be the case( 2 August, p 40 ). For example, the making and drinking of …

It is no surprise to me that napping during the day by pre-schoolers doesn't significantly impair education, reduce nighttime slumber or lead to involuntary insomnia in parents. That such research is required might baffle those who lead a traditional Mediterranean lifestyle( 26 July, p 18 ). Perhaps we should take a leaf out of our …

Your article on how to think about the weak and strong anthropic principles (AP) took the Barrow and Tipler formulations. These conflict with the original Brandon Carter definitions, make much less sense and haven't enjoyed much peer acceptance( 28 June, p 32 ). Carter's weak AP is that within a universe capable of supporting intelligent …

You report that irritable bowel syndrome (IBS) could be a nocebo effect for some people. I have for several decades relied on the opposite effect from what I call my "placebo tablets". They keep me IBS symptom-free despite having only a few Lactobacilli and Bifidobacteria, along with minerals and vitamins( 2 August, p 17 ).

As a child, I asked my father: what is infinity? He said that it was the length of the Forth Bridge as experienced by a mouse. He was an engineer. I have always found that definition most satisfactory( 9 August, p 28 ).

Above its "entropy catastrophe" temperature, a solid has higher entropy than its liquid, so melting would break the second law of thermodynamics ( 2 August, p 16 ). The pineal gland secretes melatonin ( 2 August, p 30 ).