Reading — 2026 Jan–Apr Recall Set 81

The dinosaurs may have risen to power in as little as 10,000 years. Everybody knows that the dinosaurs became extinct as a result of a large asteroid; something big hit the Earth 65 million years ago and, when the dust had fallen, so had the great reptiles. There is thus a nice, if ironic, symmetry in the idea that a similar impact brought about the dinosaurs’ rise. That is the thesis proposed by Paul Olsen of Columbia University. Dinosaurs first appear in the fossil record 230 million years ago, during the Triassic period. But they were mostly small, and they shared the Earth with lots of other sorts of reptile. It was in the subsequent Jurassic period, which began 202 million years ago, that they overran the planet and turned into the monsters realistically depicted in modern books and movies. Dr Olsen and his colleagues are not the first to suggest that the dinosaurs inherited the Earth as the result of an asteroid strike. But they are the first to show that the takeover did, indeed, happen in a geological eye-blink. Dinosaur skeletons are rare. Dinosaur footprints are, however, surprisingly abundant. And the size of the prints is as good an indication of the size of the beasts as are the skeletons themselves. Dr Olsen and his colleagues therefore concentrated on prints, not bones. The prints in question were made in Eastern North America, a part of the world then full of rift valleys similar to those in East Africa today. Like the modern African rift valleys, the Triassic/Jurassic American ones contained lakes, and these lakes grew and shrank at regular intervals because of climatic changes. Rocks from this place and period can be dated to within a few thousand years. As a bonus, squishy lake-edge sediments are just the things for recording the tracks of passing animals. By dividing the labour between them, the research team were able to study such tracks at 80 sites and look at 18 so-called ‘ichnotaxa’. These are recognisable types of footprint that cannot be matched precisely within the species of animal that left them. But they can be matched with a general sort of animal, and thus act as an indicator of the fate of that group, even when there are no bones to tell the story. Their findings show that five of the ichnotaxa disappear before the end of the Triassic, and four march confidently across the boundary into the Jurassic. Six, however, vanish at the boundary, or only just splutter across it; and three appear from nowhere, almost as soon as the Jurassic begins. That boundary itself is suggestive. The first geological indication of the impact that killed the dinosaurs was an unusually high level of iridium in rocks at the end of the Cretaceous period, when the beasts disappear from the fossil record. Iridium is normally rare at the Earth’s surface, but it is more abundant in meteorites. When people began to believe the impact theory, they started looking for other Cretaceous-end anomalies. One that turned up was a surprising abundance of fern spores in rocks just above the boundary layer – a phenomenon known as the ‘fern spike’. That matched the theory nicely. Many modern ferns are opportunists. They cannot compete against plants with leaves, but if a piece of land is cleared by, say, a volcanic eruption, they are often the first things to set up shop there. An asteroid strike would have scoured much of the Earth of its vegetable cover, and provided a paradise for ferns. A fern spike in the rocks is thus a good indication that something terrible has happened. The surprises are how rapidly the new ichnotaxa appeared and how quickly they increased in size. Dr Olsen and his colleagues suggest that the explanation for this may be a phenomenon called ecological release. This is seen today when reptiles (which in modern times tend to be small creatures) reach islands where they face no competitors. The most spectacular example is on the Indonesian island of Komodo, where local lizards have grown so large that they are often referred to as dragons. The dinosaurs, in other words, could flourish only when the competition had been knocked out. That leaves the question of where the impact happened. No large hole in the Earth’s crust seems to be 202 million years old. It may, of course, have been overlooked. Old craters are eroded and buried, and not always easy to find. Alternatively, it may have vanished. Although continental crust is more or less permanent, the ocean floor is constantly recycled by the tectonic processes that bring about continental drift. There is no ocean floor left that is more than 200 million years old, so a crater that formed in the ocean would have been swallowed up by now. There is a third possibility, however. This is that the crater is known, but has been misdated. The Manicouagan ‘structure’, a crater in Quebec, is thought to be 214 million years old. It is huge – some 100 kilometres across – and seems to be the largest of between three and five craters that formed within a few hours of each other as the lumps of disintegrated comet hit the Earth one by one. Such an impact would surely have had a perceptible effect on the world, but the rocks from 214 million years ago do not record one. It is possible, therefore, that Manicouagan has been misdated. That will be the next thing to check.

A At a course for fathers-to-be in New York, participants are introduced to baby maintenance for beginners: how to keep their babies fed, warm and clean. The City Dads Group was founded when Matt Schneider and Lance Somerfeld became fathers and discovered that people saw their place as firmly outside the home. New York was full of parents’ support groups, but nearly all were aimed at mothers. Frustrated, the friends set up their own group, which has spread to 17 cities in the USA, helping fathers who want to get involved from day one. B In general, legal and financial support for new parents is better than it has ever been. According to the International Labour Organization (ILO), 85% of countries now provide at least 12 weeks’ maternity leave. In all but two of the 185 countries it surveys, mothers are entitled to some leave paid for by the state, companies or some combination of the two. Although only a third of countries meet the ILO’s recommended minimum of at least 14 weeks off for new mothers, paid at two-thirds their salary and funded publicly, the picture is improving. But how many countries meet the ILO’s guidelines on paternity leave? None, because no such guidelines exist. Though it publishes detailed advice regarding female employees, the organisation has drawn up no formal recommendations on fathers’ rights and duties. Until recently, national governments have been similarly uninterested; less than half of countries offer paternity leave of any sort. Only around half a dozen offer new fathers more than a fortnight, and companies, not the state, usually foot the bill for the costs of paternity leave. In the eyes of most people, responsibility for bringing up baby still falls squarely on the mother. C Now a different view is slowly emerging, as growing evidence suggests that children benefit from seeing more of their fathers. But much of the demand for a shift in approaches to childcare has come from women, who have started to conclude that they are victims as well as beneficiaries of generous maternity-leave policies. D This may appear paradoxical, as most countries have found that when they offer decent maternity leave, they increase female employment. If women have no right to take time off, or are entitled only to short or poorly paid spells of absence, many have little choice but to leave the workforce when their baby is born. If they can take a few months of paid leave before returning to their old job, they are more likely to continue working. But it turns out that long maternity breaks have unintended consequences. Time away from the labour market reduces women’s earning power, as their skills degrade and they miss chances to gain experience and win promotion. Moving into senior management becomes particularly hard, partly because of discrimination by bosses and hiring committees, who reject candidates they think may be away a lot, and partly because many high-level jobs are hard to combine with serial leave-taking. And the effect is magnified when lengthy maternity leave is combined with policies to encourage part-time work, which tempt more women back into the labour force but help keep them in junior positions. E Rather than simply cutting maternity leave in response to such findings, a growing number of governments are trying to spread the child-rearing burden (or joy, depending on how one looks at it). Britain recently became the latest country to combine maternity and paternity leave into a single chunk of parental leave, to be split between mother and father however they see fit. Several European countries, as well as Australia and New Zealand, already have such a system. The problem is that dads tend not to take up the offer. In Austria, the Czech Republic and Poland, where all parental leave is transferable, only about 3% of dads make use of it. In Britain, the government estimates that only 2–8% of dads will take more than their existing fortnight. The main reason for low take-up by fathers is financial: even pre-childbirth, women are paid less than men, meaning that their salaries are easier to forgo during a period of unpaid or low-paid leave. But pressures related to culture also weigh heavily. Mothers still tend to be seen as the main carers, with dads portrayed in domestic terms as blundering sidekicks or well-meaning buffoons. F To overcome these obstacles, some countries are giving fathers a firm nudge. In a few, including Chile, Italy and Portugal, paternity leave is compulsory. Others offer incentives that are hard to turn down. Sweden grants a bonus to parents who share leave more equally. Swedish fathers now account for more than a fifth of all parental leave taken, compared with almost none when shared leave was introduced. Germany introduced the same system and saw the proportion of fathers taking time off rise from 3% in 2006 to 32% in 2013, and Poland has switched to gender-specific quotas, replacing the previous system of shared leave. Where leave is well-paid and not seen as ‘belonging’ to the mother, fathers seem willing to request it. State meddling in what has historically been regarded as a natural division of labour may annoy some people. But traditional maternity leave, which channels men into breadwinning and women into child-rearing, is hardly neutral. And shared involvement by parents stands to improve women’s careers, children’s development and perhaps even dads’ life satisfaction.

Most social scientists stubbornly resist the idea that animals have culture. Even such advanced cetacean mammals as whales and dolphins clearly don’t have art, literature, or architecture. But patient observation over many years has begun to reveal behaviours that can only be learnt from other whales. And that, say whale biologists, constitutes culture. So far, humpback and killer whales provide the best evidence of culture in cetaceans, and the song of the male humpback is among the most striking examples. Humpback populations in different oceans sing different songs, but within the same ocean they all stick to the same one. However, during the breeding season the sounds change, as it appears that females are drawn to novel songs. One male might add an extra set of groans; another might drop a series of grunts. Soon all the other males have altered their own rendition to incorporate the changes until they are once again singing the same song. Since this occurs among thousands of whales spread across a vast part of the planet, the change cannot be in response to any factor in the animal’s environment. The latest version of the song can be learnt only from other whales – almost certainly by imitation. Culture plays an even bigger part in the life of killer whales. Nowhere is this more obvious than along the north-west coast of America, where killer whales are split into two distinct populations – ‘residents’ and ‘transients’. They live in the same stretch of water, but they don’t mingle. In effect, they belong to two quite separate cultures. Residents live in stable groups, or ‘pods’, made up of two or three mothers and their offspring – perhaps 20 whales in all. Calves stay with their mothers throughout adulthood, and in many years of observation no one has ever seen a whale switch pods. Transients travel in smaller, more changeable groups of between three and six. One of the most obvious distinctions between the transient and resident societies is the way they impart information. Killer whales detect prey with a range of echo-locating clicks, but converse with a vocabulary of squeaks, whistles and whines. Transients have only a few such calls, and all transient societies share the same ones. Residents have a much more extensive repertoire, and each family group has its own unique and distinctive set of calls. Despite regular interaction between them, each resident pod sticks firmly to its own dialect. Research shows these dialects are maintained for at least 40 years. To qualify as part of killer whale culture, dialects must be learnt from other members of the pod. Animals with different dialects share the same waters, so the variation can’t be a product of physical environment. ‘And we can throw out the notion that dialects are inherited,’ says Lance Barrett-Lennard of the University of British Columbia. He has spent the past seven years analysing DNA from 270 whales. His paternity tests reveal that female killer whales invariably attract mates from outside their own pod – males with a very different dialect. If dialects were programmed by genetics, call patterns from both father and mother would be passed on to the calf. ‘A calf uses the calls of its maternal pod very precisely. There’s no input from the father,’ says Barrett-Lennard. The question still remains – is this culture? It is, according to Frans de Waal of Emory University in Atlanta, who argues that culture is just another biological adaptation that has evolved in many creatures. One benefit of viewing culture in this way is that you can start to understand how and why it might have arisen in these creatures. Whales have several biological attributes that give them an advantage in social learning. Apart from their advanced mental abilities, they are adept at recognising sounds: ideal for communicating in the marine environment. Many species spend years rearing their offspring, and live in small, stable, multi-generational societies, a social system that provides ample opportunity for teaching and learning. But why have cetaceans evolved the ability to learn from other group members? Experts in whale biology believe that ecological factors and the need to adapt to sudden changes in the environment played a large part in the emergence of culture. Although the ocean is a relatively stable habitat in many ways, it is highly changeable in one crucial respect – the availability of food. One moment there might be a plentiful supply of fish, the next they’ve disappeared. When that happens, the past experience of senior members of the group – and the ability to share this knowledge – is a huge asset. The dialects of killer whales allow members of the group to identify each other, enabling them to share information about food hot spots. Among resident killer whales, it also allows females to avoid inbreeding by picking out a mate with a strange dialect from outside their pod, says Barrett-Lennard. The importance of sharing information seems to have led to biological changes in at least some species of whale. Female killer whales, like humans, are very unusual in that they live up to a quarter of a century after they have had their descendants. And what whale matriarchs offer is the most important thing of all – cultural knowledge, vital for the group’s survival, passed directly from one generation to the next.