Last Word is 91av’s long-running series in which readers give scientific answers to each other’s questions, ranging from the minutiae of everyday life to absurd astronomical hypotheticals. To answer a question or ask a new one, email lastword@newscientist.com
Which animals can recognise individual people? Are there fish, reptiles or insects that can do this?
Justin Baker
Melbourne, Australia
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Does Earth’s mass remain constant, or is it slowly gaining or losing any?
Rod Hunt
Maidenhead, Berkshire, UK
To answer this question – or ask a new one – email lastword@newscientist.com.
Questions should be scientific enquiries about everyday phenomena, and both questions and answers should be concise. We reserve the right to edit items for clarity and style. Please include a postal address, daytime telephone number and email address.
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