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Written in stone
THE LAST WORD Tiger, tiger Why do tigers have stripes? The other big cats tend to have spots.
n The beautiful striped markings on tigers’ coats are unique in the cat family. Other closely related big cats have spotty rosette or cloud-shaped body markings (leopards, jaguars and clouded leopards), or plain coats (lions). Work by our team at the University of Bristol has shown that cat patterning evolved to provide camouflage suited to the cats’ particular habitats and behaviours, enabling them to capture prey more effectively (and escape predation in the case of the smaller cats). In general, plainer species such as lions live in open environments and hunt by day, whereas cats with complex patterning like leopards and tigers have more nocturnal habits and live in environments with more trees. Our statistical analysis nicely supports common-sense natural history. Unfortunately, with no other striped cats around besides tigers, we cannot use the same methods to identify the evolutionary factor which drove tigers to depart from the ancestral big-cat pattern. Tigers are much bigger than jaguars and leopards, but in general they have a similar ecology, and tigers’ historical range and habitat utilisation overlap considerably with those of leopards. So why don’t they look similar? One idea put forward decades
Questions and answers should be concise. We reserve the right to edit items for clarity and style. Include a daytime telephone number and email address if you have one. Restrict questions to scientific enquiries about everyday phenomena. The writers of published answers will receive a cheque for £25 (or US$ equivalent). Reed Business Information Ltd reserves all rights to reuse question and answer material submitted by readers in any medium or format.
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ago, but for which evidence is still lacking, is that compared with the typical leopard habitat, the average tiger habitat contains a lot of vertical features such as bamboo. Quantifying this would be straightforward except that with the tigers’ range now so shrunken, it is hard to know exactly what sort of forest their coat evolved in. Tigers are obviously well camouflaged, yet the factors behind their appearance remain an enigma. Intriguingly, our team has also shown that big-cat patterning changes relatively rapidly over evolutionary timescales. One day our descendants might wonder at the beauty of striped leopards and spotty tigers. Will Allen University of Bristol, UK
Written in stone I spotted these stones used to make walls in Gozo, Malta (see photo). What aspect of composition and weathering led to their distinctive indented appearance?
n The picture shows a type of stone known as a globigerina limestone, which is the traditional building stone of choice in Malta and Gozo. While easy to quarry and cut to shape, it has the disadvantage of being very prone to salt weathering, a process in which salts crystallise within pores in the stone and can eventually cause it to erode and crumble. In this case the salts are probably deposited by sea spray,
New Scientist retains total editorial control over the content of The Last Word. Send questions and answers to The Last Word, New Scientist, Lacon House, 84 Theobald’s Road, London WC1X 8NS, UK, by email to [email protected] or visit www.last-word.com (please include a postal address in order to receive payment for answers). For a list of all unanswered questions send an SAE to LWQlist at the above address.
although in towns they may be derived from pollution. Weathering could be the result of the salts repeatedly dissolving and recrystallising. The effectiveness of this process is very sensitive to the size, shape and connectedness of the pores within the stone, and the pattern of decay often reflects subtle variations in the grain size and porosity. In a completely uniform stone, salt weathering often begins at seemingly random locations and excavates small hollows which, as they expand and meet, create a characteristic honeycomb structure. Where there are variations in the stone’s texture, salt weathering will accentuate them. This is what happens in many examples of globigerina limestone, which is a marine sediment made up of fragments of shells and other organic debris the size of grains of sand. Other
organisms burrowed into the stone as it was laid down, and their burrows were subsequently filled in with debris that was slightly different from that of the surrounding sediment. These areas act as so-called “trace fossils” in that they are a marker of biological activity. Their presence is picked out by salt weathering, when they distort what would otherwise be a regular honeycomb pattern of erosion. Bernard Smith School of Geography, Queen’s University Belfast, UK
This week’s question Toothpick please
Why do bits of pork and corn on the cob get stuck between my teeth more than any other food? I used to think it was just me until a friend, unprompted, said the same thing. Gene Sossick Lille, France
Why can’t elephants jump? The latest collection: witty, brilliant, intelligent and packed with insight Available from booksellers and at www.newscientist.com/elephants
n The beautiful striped markings on tigers’ coats are unique in the cat family. Other closely related big cats have spotty rosette or cloud-shaped body markings (leopards, jaguars and clouded leopards), or plain coats (lions). Work by our team at the University of Bristol has shown that cat patterning evolved to provide camouflage suited to the cats’ particular habitats and behaviours, enabling them to capture prey more effectively (and escape predation in the case of the smaller cats). In general, plainer species such as lions live in open environments and hunt by day, whereas cats with complex patterning like leopards and tigers have more nocturnal habits and live in environments with more trees. Our statistical analysis nicely supports common-sense natural history. Unfortunately, with no other striped cats around besides tigers, we cannot use the same methods to identify the evolutionary factor which drove tigers to depart from the ancestral big-cat pattern. Tigers are much bigger than jaguars and leopards, but in general they have a similar ecology, and tigers’ historical range and habitat utilisation overlap considerably with those of leopards. So why don’t they look similar? One idea put forward decades
Questions and answers should be concise. We reserve the right to edit items for clarity and style. Include a daytime telephone number and email address if you have one. Restrict questions to scientific enquiries about everyday phenomena. The writers of published answers will receive a cheque for £25 (or US$ equivalent). Reed Business Information Ltd reserves all rights to reuse question and answer material submitted by readers in any medium or format.
Last words past and present, plus questions, at www.last-word.com
ago, but for which evidence is still lacking, is that compared with the typical leopard habitat, the average tiger habitat contains a lot of vertical features such as bamboo. Quantifying this would be straightforward except that with the tigers’ range now so shrunken, it is hard to know exactly what sort of forest their coat evolved in. Tigers are obviously well camouflaged, yet the factors behind their appearance remain an enigma. Intriguingly, our team has also shown that big-cat patterning changes relatively rapidly over evolutionary timescales. One day our descendants might wonder at the beauty of striped leopards and spotty tigers. Will Allen University of Bristol, UK
Written in stone I spotted these stones used to make walls in Gozo, Malta (see photo). What aspect of composition and weathering led to their distinctive indented appearance?
n The picture shows a type of stone known as a globigerina limestone, which is the traditional building stone of choice in Malta and Gozo. While easy to quarry and cut to shape, it has the disadvantage of being very prone to salt weathering, a process in which salts crystallise within pores in the stone and can eventually cause it to erode and crumble. In this case the salts are probably deposited by sea spray,
New Scientist retains total editorial control over the content of The Last Word. Send questions and answers to The Last Word, New Scientist, Lacon House, 84 Theobald’s Road, London WC1X 8NS, UK, by email to [email protected] or visit www.last-word.com (please include a postal address in order to receive payment for answers). For a list of all unanswered questions send an SAE to LWQlist at the above address.
although in towns they may be derived from pollution. Weathering could be the result of the salts repeatedly dissolving and recrystallising. The effectiveness of this process is very sensitive to the size, shape and connectedness of the pores within the stone, and the pattern of decay often reflects subtle variations in the grain size and porosity. In a completely uniform stone, salt weathering often begins at seemingly random locations and excavates small hollows which, as they expand and meet, create a characteristic honeycomb structure. Where there are variations in the stone’s texture, salt weathering will accentuate them. This is what happens in many examples of globigerina limestone, which is a marine sediment made up of fragments of shells and other organic debris the size of grains of sand. Other
organisms burrowed into the stone as it was laid down, and their burrows were subsequently filled in with debris that was slightly different from that of the surrounding sediment. These areas act as so-called “trace fossils” in that they are a marker of biological activity. Their presence is picked out by salt weathering, when they distort what would otherwise be a regular honeycomb pattern of erosion. Bernard Smith School of Geography, Queen’s University Belfast, UK
This week’s question Toothpick please
Why do bits of pork and corn on the cob get stuck between my teeth more than any other food? I used to think it was just me until a friend, unprompted, said the same thing. Gene Sossick Lille, France
Why can’t elephants jump? The latest collection: witty, brilliant, intelligent and packed with insight Available from booksellers and at www.newscientist.com/elephants