Sharing is caring

Altruism- sounds like a complicated word but in reality, has quite a nice meaning. Altruism is any behaviour that disadvantages the actor but has benefits for others, usually seen in social animals. There are many suggested reasons for altruism in animals; one reason is genetic benefits called ‘kin selection’ whereby if one animal helps it’s relative survive, that relative has more chance of surviving and indirectly passing on its relative's genes to the next generation- known as Hamilton’s rule [1]. Another reason for altruism is selfish benefits whereby an animal does something nice for another animal with the incentive that this favour will be returned- known as reciprocal altruism [1]. Altruism puzzles evolutionary scientists because, as Joey says, there is no truly selfless deed! There are many examples of altruism in animals; some can easily be explained, such as ants who give up reproductive rights for their queen so she can produce (explained by kin selection) [1] and some can’t, such as a group of sperm whales who raised a bottlenose dolphin calf [2].

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One of my favourite examples of altruism exists in vampire bats. Female vampire bats will share food (in their case-blood) with other female friends to help them survive [3]. Vampire bats feed on small portions of animal blood without causing long-lasting harm and live in social groups of many unrelated females with males living solo [3,4]. Vampire bats rely heavily on their daily meals of blood whereby if two daily meals are missed, the bat will starve, so they share regurgitated blood to ensure the survival of their friends [3]. This behaviour was previously thought to be explained by kin-selection or harassment, whereby if vampire bats shared with non-related individuals it was down to poor kin-recognition, or they did not have the energy to refuse harassers [5]. However, Carter and Wilkinson’s study suggest 64% of sharing groups were unrelated [5]. Food is such a key element to vampire bat's survival, especially females who are responsible for their offspring’s survival for nine months [3]. This confuses researchers: if females aren’t focussed on sharing meals with family members to ensure the survival of familial genes, then why would these females go out and use energy in a hunt and then come home and share it with non-related others? It was found that these females form complex social connections as a safety net so that if their family die and cannot provide them with food, then they can rely on others [4].

Carter and Wilkinson’s study showed that female bats will share food based on food received from others- food received was 8.5 times more influential than relatedness in who the bats shared their food with [5]. Also, it was the donors who initiated food sharing, not recipients, this removes harassment as a cause for sharing [5]. This suggests that food sharing in vampire bats is due to reciprocal altruism whereby bats feed bats who will later on feed them , this is because it provides mutual direct fitness benefits [5] and ensures the survival of the vampire bat’s friends so they can repay them later and provide them with other benefits such as allo-grooming.

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In some scenarios, vampire bats did deny giving others free food because they simply couldn’t afford it, however, when the donors were able to provide their friend with some food, they would give even more than normal, to make up for the fact that they had been a ‘bad friend’ in the past [3]. This suggests these social groups are more complex than ‘just friends’, these bats keep track of whom will give them food when they need it and will go out of their way to ensure relationships aren’t damaged in situations where they previously may have let a friend down [3]. Over time these bats build a group of around 4 bats they can trust to share food and ensure their survival [5]- what good friends! This creates what is known as a biological market in these bats, where they trade commodities (such as blood and allo-grooming) with people they trust for delayed payment (blood and allo-grooming).

I think these bats show almost human-like behaviours in terms of helping others with no immediate benefit to themselves. In most species, it’s thought they will let nature take its course- if you can’t hunt effectively, you will die and your poor hunting genes won’t be passed on in the population. However, these bats have taken it a step further and are willing to remove individual selection pressures (such as in-availability of food) by sharing so that they don’t die. These bats will weigh up the costs and benefits of this situation and won’t give more than they can handle if they aren’t getting anything in return, but that is nature. Some studies even suggest these societies in bats reflect on our human societies where we create networks of people outside our family whom we can rely on in our time of need- we can turn to our neighbour [4]. Overall, these amazing bats show complex social organisations based on the trust that the commodities and benefits they provide, will be returned in a delayed payment scheme- get your food now but pay me back later. This potentially shows delayed gratification seen in only a few species by the marshmallow test and could be further studied. I wonder how much these animals would give up for their friends?