Do not dare call me a bear
QUESTION Why can’t koalas survive without eucalyptus leaves?
EUCALYPTUS leaves are fibrous and toxic, so in order to eat them, koalas (Phascolarctos cinereus) have developed radical and specialised physical adaptations, which has led the species down an evolutionary dead-end.
The fossil pollen record shows there have been eucalyptus trees in Australia for 45 million years. They have a remarkable ability to quickly re-sprout from dormant buds after droughts or fires.
As eucalyptus became dominant, koalas developed detoxification proteins in the liver. The greater glider and ringtail possum are the only other animals known to be able to eat these toxic leaves.
Many mammals have a fibredigesting organ called a caecum, but the koala’s is two metres long compared to just 6cm in humans.
It contains millions of bacteria that break down the fibrous eucalyptus leaves into substances that are easier to absorb.
Koalas have a very slow metabolic rate, which means they retain food in their digestive system for a long time, maximising the amount of energy and moisture extracted from such a poor energy source. Koalas sleep between 18 and 22 hours a day to digest and conserve energy, and rarely need to drink.
These unique adaptations mean koalas are unable to eat anything other than eucalyptus leaves.
Koalas are not bears, but are marsupials that split from the wombat family 35 million years ago. Their bear-like appearance is thought to be related to their reliance on eucalyptus. By studying the skulls of koala ancestors, palaeontologists at the University of New South Wales concluded that evolution reshaped the animals’ faces to enable them to eat eucalyptus leaves while communicating over long distances.
To make the bellowing grunts that belie their cuddly appearance, koalas have an extra pair of vocal folds outside the larynx, where the oral and nasal cavities connect. It’s thought that as the Australian climate became drier, the forests became less dense and koalas produced ever lower frequency sounds that could travel further. To hear these frequencies, they evolved round ears with an extremely large middle ear. An elongated jaw gives them the chewing power to deal with the tough eucalyptus leaves. This combination of evolutionary quirks appears to have created their bear-like appearance.
Tom Davies, Gerringong, New South Wales.
QUESTION What caused the mysterious 2019 oil spill on Brazil’s beaches?
IN August 2019, large quantities of oil began to wash up along Brazil’s north-east coast, causing significant damage. More than 5,000 tonnes has been cleared up from 1,500 miles of sandy beaches. The oil has contaminated estuaries, beaches, mangroves and reefs. Despite many theories and accusations, the source of the oil remains a mystery.
The origin of oil can be difficult to identify, but it does carry chemical fingerprints, depending on its source.
Research by the Brazilian state oil company, Petrobras, suggested it was not to blame and chemical analysis by the country’s environmental agency Ibama agreed the spill did not match oil from Brazil. Gas chromatography results have suggested the oil could be of Venezuelan origin, a suggestion that has been denied.
In November 2020, after analysing 826 satellite images, the Brazilian Federal Police attributed the disaster to a leak from the Greek-flagged tanker Bouboulina, carrying heavy crude oil from Venezuela in July 2019. But its owners have categorically denied this.
Dr Ken Warren, Glasgow.
QUESTION Who invented the theodolite?
THIS is a surveying instrument mounted on a tripod with adjustable legs. It is used to obtain precise angular measurements for triangulation.
English mathematician Leonard Digges is credited with the invention of the theodolite in 1550. He was certainly the first to use the term theodolitus to describe the instrument in his book Pantometria, published by his son Thomas in 1571.
The name resembles a Greek word, but there is no obvious source for it. It’s been surmised it could come from thea meaning prospect and delo, make visible. Or that it was constructed from three words: itheomai, meaning see; odos for path; and litos meaning smooth or plain.
The 19th century mathematician Professor Augustus De Morgan suggested that theodolite was related to alidade, a device that allows you to use the line of sight from a distant object to perform a task. He thought the word was a corruption of the Arabic word alidhada meaning a sort of rule, but this is not widely accepted.
Another suggestion is that it was named in honour of a mathematician named Theodolus. Unfortunately, the best known Theodolus was active a century after Digges’s invention.
It took two centuries of adaptations and improvements for the theodolite to reach its final basic form. The great theodolite invented by Jesse Ramsden in 1787 was made up of a telescope mounted on a compass, or a quadrant plus a circle and compass. This revolutionised surveying and led to the establishment of the Ordnance Survey.
Emma Lister, St Ives, Cornwall.
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