Latest news with #evolution
Telegraph
21 hours ago
- Health
- Telegraph
Why cats prefer sleeping on their left side
Cats prefer to sleep on their left side to protect themselves from predators, a study has found. The pets sleep for up to 16 hours a day and often curl up or stretch out for a snooze in opportune places. But the way the animal settles down is not random, and there is an evolutionarily hard-wired logic underpinning it, according to a study from the Ruhr University Bochum in Germany. Scientists found cats lie on their left side around two-thirds of the time, which shows that it was done deliberately. They looked at clips on YouTube of more than 400 sleeping cats and logged which side they were sleeping on. Data revealed that 266 of the cats (66.5 per cent) were on their left side, leaving scientists to conclude this was a survival trait from their history in the wild. Sleeping on their left side means when they wake, their left eye is able to see the local area unobstructed by the cat's own body. This visual information is then processed by the right side of the brain. This hemisphere is what processes threats and is responsible for escaping danger as well as knowing an individual animal's position. This puts the cat at an advantage compared to if it was to sleep on its right side – when the information is processed by the left side of the brain, which is less specialised to aid a swift escape. Anti-predator vigilance This leftward preference is just one of the many ways in which cats protect themselves. 'Sleep is one of the most vulnerable states for an animal, as anti-predator vigilance is drastically reduced, especially in deep sleeping phases,' according to the study. 'Domestic cats are both predators and prey (e.g. for coyotes) and sleep an average of 12–16 hours a day. 'Therefore, they spend almost 60-65% of their lifetime in a highly vulnerable state. To reduce predation risks, cats prefer to rest in elevated positions so that predators are more visible to them and the cats, in turn, are more visually concealed from predators. 'In such a spot, predators can access cats only from below. Thus, their preference for resting in an elevated position can provide comfort, safety, and a clear vantage point for monitoring their environments. 'We hypothesised that a lateralised sleeping position further increases the chances of quickly detecting predators (or to identify careless prey) when awoken.' Threat-processing leftward bias Pregnant cows are known to prefer their left side while sleeping for a similar reason, experts believe. The scientists also found that the pawedness of a cat, whether it preferred its left or right side, is likely not to blame for the sleeping preference. A 2017 study found that male cats tend to prefer their left paws and females are more right-paw dominant. 'We are inclined to believe that the significant leftward bias in sleeping position in cats may have been evolutionarily driven by hemispheric asymmetries of threat processing,' the scientists add in their paper, published in the journal Current Biology.
The Independent
a day ago
- Science
- The Independent
Why our chins remain an evolutionary mystery
Scientists are still trying to understand the evolutionary reasons behind unique human features, such as the chin and the relative size of testicles. The concept of convergent evolution, where a feature evolves multiple times independently, serves as a natural experiment to determine the purpose of body parts. Analysis of testicle size across various mammals, including monkeys, gorillas, chimps, and dolphins, reveals a consistent correlation between larger testicles and promiscuous mating behaviors. This correlation suggests that larger testicles evolved to facilitate sperm competition in species with multiple partners, with human testicle size falling in the middle. The human chin remains an evolutionary mystery because its uniqueness among mammals, including Neanderthals, prevents the use of convergent evolution to test hypotheses about its purpose.
The Independent
a day ago
- Science
- The Independent
The unique human body part that evolution cannot explain
The human body is a machine whose many parts – from the microscopic details of our cells to our limbs, eyes, liver and brain – have been assembled in fits and starts over the four billion years of our history. But scientists are still puzzling over why we evolved into this particular form. Why do humans uniquely have a chin, for example? And why, relative to body weight, is a human testicle triple the size of a gorilla's but a fifth of that of a chimpanzee? As I show in my new book, The Tree of Life, we are still searching for the answers to many of these 'why' questions. But we are starting to find answers to some of them. The story of evolution tells us how, starting from simple beginnings, each species was built, when each of the components that make a living creature was added to its blueprint. If we climb the evolutionary tree of life, we can follow a twisting path that visits the increasingly specialised branches that a species belongs to. We humans, for example, were animals before we became vertebrates; mammals before evolving into primates and so on. The groups of species we share each of these branches with reveal the order our body parts appeared. A body and a gut (inventions of the animal branch) must have come before backbone and limbs (vertebrate branch); milk and hair (mammals) came before fingernails (primates). There is a way we can study the separate problem of just why we evolved each of these body parts, but it only works if the feature in question has evolved more than once on separate branches of the tree of life. This repeated evolution is called convergence. It can be a source of frustration for biologists because it confuses us as to how species are related. Swallows and swifts, for example, were once classified as sister species. We now know from both DNA and comparisons of their skeletons that swallows are really closer relatives of owls than swifts. Size matters when it comes to evolution But convergent evolution becomes something useful when we think of it as a kind of natural experiment. The size of primate testicles gives us a classic example. Abyssinian black and white colobus monkey and bonnet macaque adult males are roughly the same size. But, like chimps, humans and gorillas, these similar monkeys have vastly dissimilar testicles. Colobus testicles weigh just 3 grams. The testicles of the macaques, in contrast, are a whopping 48 grams. You could come up with several believable explanations for their different testicle sizes. Large testicles might be the equivalent of the peacock's tail, not useful per se but attractive to females. But perhaps the most plausible explanation relates to the way they mate. A male colobus monkey competes ferociously for access to a harem of females who will mate exclusively with him. Macaques, on the other hand, live in peaceful mixed troops of about 30 monkeys and have a different approach to love where everyone mates with everyone else: males with multiple females (polygamy) and females with multiple males (polyandry). The colobus with his harem can get away with producing a bare minimum of sperm – if a droplet is enough to produce a baby, then why make more? For a male macaque, the competition to reproduce happens in a battle between his sperm and the sperm of other males who mated before or after. A male macaque with large testicles should make more sperm, giving him a higher chance of passing on his genes. It's a sensible explanation for their different testicle sizes, but is it true? This is where convergent evolution helps. If we look across the whole of the mammal branch of the tree of life, we find there are many groups of mammals that have evolved testicles of all different sizes. In almost all these separate cases, larger testicles are consistently found in promiscuous species and smaller in monogamous. A small-testicled, silverback male gorilla has sole access to a harem. Big-testicled chimps and bonobos are indeed highly promiscuous. Dolphins, meanwhile, may have the biggest mammalian testicles of all, making up as much as 4 per cent of their body weight (equivalent to human testicles weighing roughly 3 kilos). Although wild dolphin sex lives are naturally hard to study, spinner dolphins at least fit our expectations, engaging in mass mating events called wuzzles. It was thanks to the multiple observations provided by convergent evolution that we were able to discover this consistent correlation between testicle size and sex life right across the mammals. And as for humans, we have testicle size somewhere in the middle, you can make of this what you want! But what of the human chin? The human chin has been fertile ground for arguments between scientists over its purpose. As with testicles, there are half a dozen plausible ideas to explain the evolution of the human chin. It could have evolved to strengthen the jaw of a battling caveman. Maybe the chin evolved to exaggerate the magnificence of a manly beard. It might even be a by-product of the invention of cooking and the softer food it produced – a functionless facial promontory left behind by the receding tide of a weakening jaw. Intriguingly, however, a chin can be found in no other mammal, not even our closest cousins, the Neanderthals. Thanks to the uniqueness of the homo sapiens chin, while we have a rich set of possible explanations for its evolutionary purpose, in the absence of convergent evolution, we have no sensible way of testing them. Some parts of human nature may be destined to remain a mystery.
New York Times
a day ago
- Science
- New York Times
Honey, We Shrunk the Cod
Call it the case of the incredible shrinking cod. Thirty years ago, the cod that swam in the Baltic Sea were brag-worthy, with fishing boats hauling in fish the size of human toddlers. Today, such behemoths are vanishingly rare. A typical Eastern Baltic cod could easily fit in someone's cupped hands. Experts have suspected that commercial fishing might be to blame. For years, the cod were intensely harvested, caught in enormous trawl nets. The smallest cod could wriggle their way out of danger, while the biggest, heaviest specimens were continually removed from the sea. One simple explanation for the phenomenon, then, was that the fish were not actually shrinking: Rather, they were simply eliminated as soon as they grew big enough to be caught. But a new study suggests that intense fishing was driving the evolution of the fish. Small, slow-growing cod gained a significant survival advantage, shifting the population toward fish that were genetically predisposed to remaining small. Today's cod are small not because the big individuals are fished out but because the fish no longer grow big. The data, which were published on Wednesday in the journal Science Advances, add to a growing body of evidence that human activities like hunting and fishing are driving the evolution of wild animals — sometimes at lightning speed. 'Human harvesting elicits the strongest selection pressures in nature,' said Thorsten Reusch, a marine ecologist at the GEOMAR Helmholtz Centre for Ocean Research Kiel in Germany and an author of the new paper. 'It can be really fast that you see evolutionary change.' Want all of The Times? Subscribe.
BBC News
2 days ago
- Science
- BBC News
Shoots of hope for Britain's cherished ash trees
Ash trees are fighting back against a disease that has ravaged the British countryside, new scientific evidence ash dieback arrived in 2012, predictions suggested up to 85% of ash trees could be now scientists have discovered that ash woodlands are naturally evolving greater resistance to the discovery offers renewed hope that the much-loved trees will survive in the British landscape. "It is hope born out of the death of a lot of trees," said Prof Richard Buggs of the Royal Botanic Gardens Kew, and Queen Mary University of he said other interventions would be needed to give ash trees a helping hand, such as protecting trees from grazing deer and breeding the most resilient trees for future planting schemes."We have fresh motivation to look after our ash populations, to protect them from other problems like deer browsing, and to let nature take its course and evolve trees with more resistance," he told BBC Ash dieback fungus originated in Asia and was introduced to Europe about 30 years study of ash trees at a woodland in Surrey revealed subtle shifts over time in different genes, which should help new saplings fight back against trees are evolving greater resistance to the disease than their predecessors - an example of Charles Darwin's natural selection theory in Nichols, professor of evolutionary genetics at Queen Mary University of London, said a "tragedy for the trees has been a revelation for scientists: allowing us to show that thousands of genes are contributing to the ash trees' fightback against the fungus". Ash dieback demonstrates how devastating introduced pathogens can be for our trees and the species which rely upon them, said Rebecca Gosling of the Woodland Trust. "The findings highlight how vital it is to support natural regeneration in woodlands, furthering our understanding of how to best manage our ash woodlands," she had feared the ash would go the way of the elm, which has been almost wiped out by Dutch elm loss of the native tree would have a devastating effect on biodiversity as well as changing the face of the landscape. Since its arrival in Britain in 2012, ash dieback has spread to every corner of the British Isles, causing widespread damage to fungus genetic code unravelledAlarm call as world's trees slide towards extinctionAsh tree set for extinction in EuropeSigns of the disease can be seen through withered and blighted many cases the fungal disease will eventually kill the research is published in the journal, Science.
