Perhaps this is something we already realise and if that is the case this study confirms it. Mammals in groups live the longest. The study found a link between the social organisation of mammals and their life spans. This is a Chinese study by researchers from the Institute of Zoology at the CAS Key Laboratory of Animal Ecology and Conservation Biology in Beijing. The scientists analysed the evolutionary history and relationships within groups of mammals and those that lived solitary lives or in pairs. In all 974 mammalian species were examined. Please note: I have added a couple of personal thoughts.
The study included land-dwelling animals such as humans and monkeys, mammals that can fly such as bats and marine mammals such as whales. They looked for a correlation between lifestyle and lifespan.
They concluded that “group-living species lived longer than solitary species”. And they decided that there was an evolutionary correlation between social organisation and longevity. I take this to mean that through the process of evolution under Darwin’s theory of the survival of the fittest, the concept of living in groups developed because it enhanced survival and extended life spans.
They found no significant difference between the lifespans of species that live in pairs and those that live solitary lives. This suggests that the benefits come with living in groups and a social order.
The question is how does living in groups extend lifespan of the members of the group?
These are the following reasons as I understand the study:
- Living in a group reduces the risk of being preyed upon by a predator and it reduces the risk of starvation.
- The “strong and stable social bonds formed among group members” can have the power to “enhance longevity” according to earlier studies as well as this one.
- Living in groups can influence “cooperative breeding”. I take this to mean that there are benefits in terms of procreation which has a knock-on effect of improving group survival.
- There is an enhancement in individual health and offspring survival with the development of social hierarchies and cooperative breeding within groups.
- The scientists suggest that to maximise the chances of offspring surviving the lifespan of parents may be extended “to allow for the provision of parental care or even grandparent or care to offspring”.
Feral cat cooperation
I would like to add something that I have learned through my studies of domestic and feral cats. Feral cats often live in groups when there is a food source available. And in these groups, you will find that females sometimes share the burden of raising their kittens. This must enhance survival of the kittens which in turn improves the average lifespan of the members of the group.
Loneliness in humans
Also, it has been known for a long time that “loneliness is as much a predictor of premature death as a person’s weight” (Daily Mail). Living alone, for humans can shorten lifespan as much as obesity. People living alone can expect to live 3-5 years less on average compared to others who see themselves as not being lonely.
That information comes from a Singapore study where 40% of people aged 80 and above said that they were lonely.
Humans have the most complex society of all creatures as you might expect. Human society is interdependent where, in general, people band together in groups for mutual aid and protection.
That does not apply across the board but as I see it, even people who live alone and are lonely have the wider human society to call upon if they feel they need it.
Two wild cat species
Touching on cats again, my speciality; lions live in groups called prides. The wildcat ancestors of the domestic cat, the North African wildcat, is a solitary creature. The lifespan of lions (12-16 years in the wild) is no longer than the lifespan of the wildcat (13-14 years in the wild) in general terms. Therefore, this study doesn’t apply to every situation. Clearly there are other factors dictating lifespan.
Study title and link
Zhu, P., Liu, W., Zhang, X. et al. Correlated evolution of social organization and lifespan in mammals. Nat Commun 14, 372 (2023). https://doi.org/10.1038/s41467-023-35869-7
AI summary of the study
Living in groups can provide certain benefits to mammals that can result in longer lifespans. These benefits include increased access to resources such as food, protection from predators, and the ability to share information and knowledge. In some species, living in groups also facilitates cooperative care of young and helps to provide social support and comfort. Additionally, group living can reduce stress levels and increase overall health, which can contribute to longer lifespan. However, it is important to note that living in groups is not always beneficial and can also have drawbacks, such as increased competition for resources and increased exposure to diseases, which can offset any positive effects on lifespan.
