Why Some Mammals Have Developed A Cooperative Approach To Raising Their Young - IELTS Reading Answers & Explanations

Read the text below and answer questions 28-40.

Why some mammals have developed a cooperative approach to raising their young

A Meerkats are one of the most cooperative species of mammal on the planet. Their home is in the flat, arid landscape of the huge Kalahari Desert in Southern Africa where there is no water throughout many months of the year. The scarcity of food and the difficulty of finding anywhere suitable to hide from predators have led them to live in groups where they share the roles of food hunters. Meerkats live in large families of up to 50 individuals, but only one dominant male and female will breed, while their pups are fed and raised by the others in the group. The subordinate females produce milk for the pups and take care of them in their underground burrows during the first three weeks of life. For the next three months these females continue to provide their nutrition by giving away up to 40% of the food they find.

B This strategy is hugely successful – dominant female meerkats can produce up to 20 pups in a year, increasing their group’s size so they can hold precious land against rival families. But the evolution of this strategy makes little sense when individuals are typically out to help themselves. In most animals, the drive for survival and to pass on their own genes means few will help to raise the offspring of others and in some cases, such as lions and some monkeys, they will even kill the young of rivals. ‘It’s easy to understand why animals compete,’ said Professor Tim Clutton-Brock, a zoologist at the University of Cambridge. ‘It is less easy to understand why in some cases individuals might spend a large section of their lives helping other individuals.’

C This is what Prof. Clutton-Brock and his colleagues set out to understand as part of an ambitious six-year project. They observed and monitored more than 700 wild meerkats from 30 different groups in the Kalahari, taking genetic and hormone samples of the animals throughout their lives. They found that meerkats show an unusually high level of kinship to others in their group compared to that found in other social animals, such as African hunting dogs and primates. In other words, almost all members of a meerkat group are brothers and sisters. As the meerkats within a group all share copies of the same genes, it means they also have a vested interest in ensuring that their mother’s offspring reach adulthood, says Prof. Clutton-Brock. He explains that other females can ensure the genes they share are passed on by helping to raise their brothers and sisters. ‘It makes cooperation much stronger.’

D In other social animals, such as chimpanzees and baboons, kinship is much lower within groups. This means that higher primates, including humans, have to engage in far more social manoeuvering and alliance-forming within their group. Prof. Clutton-Brock says. This could have been one of the driving forces for the increases in intelligence and brain size seen in humans. ‘Most of the animals that live in groups with low levels of kinship tend to be what we would regard as cognitively developed,’ said Prof. Clutton-Brock. Even humans live in groups with very low average levels of relatedness. The moral is that if you are living in a group where not everyone is closely related to you and might be looking to disadvantage you if they get a chance, you need to be clever.

E Other cooperative animals have evolved different strategies to help ensure the group sticks together. Banded mongooses, the meerkats’ larger cousins, create a ‘veil of ignorance’ that helps to ensure the group work together to raise their young. Unlike meerkats, four to six females breed at the same time. While younger females typically mate a few days after the older ones, they synchronise their pregnancies so all the females give birth on exactly the same morning. The communal litter is then raised by the group. Professor Michael Cant, an evolutionary biologist at the University of Exeter, UK, who has been studying mongooses since 1995, says, ‘Synchronising to give birth at the same moment is a way to avoid infanticide. We think none of the females know who their own pups are so they care for all of them just in case they are their own.’ It is a selfish act that leads to something like a true community.

F To examine this behaviour in more detail, Prof. Cant and his team fed half of the breeding females in each mongoose group with additional nutrient-rich food during pregnancy. They found that while the mothers that had been fed the extra food gave birth to larger pups, they then worked extra hard to raise the offspring of mothers who had not had the extra food, levelling out the differences between them. ‘[Banded] mongooses always [seem to] do the opposite of what we think they should do,’ said Prof. Cant, whose assumption had been that pups who were bigger at birth would benefit from their head start in life. Instead, the females focused on raising the weakest individuals. Further results due to be published later also show that those whose mothers were not fed extra food during pregnancy may actually end up doing better in later life.

Prof. Cant believes that the results could also have implications for testing theories of cooperation in humans. ‘Humans are cooperative breeders – our offspring are raised by grandparents and siblings as well as their parents.’