Chimpanzee Orphans: Shaded Life

The loss of the mother can also have far-reaching consequences for the life of the orphaned chimpanzee. (Image: Liran Samuni, Taï Chimpanzee Project)

The early loss of a mother is bad for young people and can have a negative impact on their whole life. Apparently something similar is also the case with our closest relatives in the animal kingdom, according to a study: If self-employed but not yet sexually mature male chimpanzees lose their mothers, their subsequent reproductive success suffers. The researchers say they probably lack the knowledge that mothers normally pass on to their offspring during this developmental phase.

The intensive and long parental care is a fundamental part of the human success story. It made it possible for our ancestors to produce brains that were particularly large and powerful relative to body mass. The organs of thought require a lot of energy and grow only slowly, which necessitates a long childhood. This was accompanied by another important effect: the continuous parental care during long childhood enabled a cultural transmission: The human offspring can learn complex skills and behaviors and pass them on again.

Chimpanzee orphans in view

Although not quite as pronounced, these aspects also apply to the chimpanzees. “When we research our closest living relatives, we also learn something about which factors have made us human,” says first author Catherine Crockford from the Max Planck Institute for Evolutionary Anthropology in Leipzig (MPI-EVA). These great apes also go through an unusually long childhood phase – but there are differences to humans: Chimpanzee mothers breastfeed their children until they are four to five years old. After that, they stay in close contact with them, but rarely supply them directly with food. Most of the time, the offspring are already looking for food themselves. This means that survival without the mother is basically possible.

As part of their study, the MPI scientists, together with researchers from the Taï chimpanzee project in Ivory Coast, have now investigated the question of how the loss of the mother in this phase affects the further life of male offspring. As they explain, the focus has been on the male offspring, as as adults they remain in the same community as their mothers, while females often move to other communities. For the study, the researchers evaluated data from three groups of chimpanzees that have been studied for over thirty years. They include behavioral studies, information about connections among animals, as well as genetic samples that enable paternity testing.

Far-reaching consequences of orphanage

As the researchers report, the data from twelve male chimpanzees who lost their mothers after weaning but before reaching sexual maturity showed that, on average, they produced significantly fewer offspring later than eleven comparison males who did not the early loss were affected. In contrast to these, the orphaned males only spent about half as much time in alpha male positions, according to the data analyzes. “Our study shows that in chimpanzees, too, the presence and care of the mother during a particularly long childhood has an important influence on the fitness of her children. It seems that our last common ancestor with the chimpanzee already possessed these important maternal traits, which could have had a significant impact on the evolution of humans and chimpanzees, ”says Crockford.

Now, however, there is still the question of what chimpanzee mothers can offer their sons that gives them a competitive advantage. Based on the data collected, there are some possible explanations, say the researchers: “Mothers know where to find the best food and how they can use tools to get hard-to-reach foods such as insects, honey and nuts that are particularly nutritious”, says Crockford. “Chimpanzee children and adolescents learn these skills only gradually. The acquisition of skills that give the young animals access to particularly nutritious food could be one reason why great apes can afford a brain that is much larger in relation to their body size than other primates, ”says the researcher.

“Another explanation is that mothers pass on social skills,” says co-author Roman Wittig from the Taї chimpanzee project. “Similar to humans, chimpanzees also live in a complex social environment with alliances and competition. By observing their mothers, young animals may learn in which situations they form alliances and in which they have to fight, ”says the scientist.

Source: Max Planck Institute for Evolutionary Anthropology, specialist article: Science Advances, doi: 10.1126 / sciadv.aaz5746

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