03.11.2022 – Grandma effect

Published by Fatima Kutzschbach on November 11, 2022

Today I had a very interesting conversation with a guest on our morning cruise on the Ribeira Brava. John coordinates and directs research projects in Finland. He addressed the grandmother effect! In Finland, the old church registers were examined more closely. They functioned as a kind of prehistoric “Facebook”. Not only marriages, births and deaths were recorded in these church books, but also hobbies, preferences, departure of the population etc. recorded. Among other things, a very important detail was entered there. It was about whether the grandmothers lived with the family or somewhere else. On later inspection, a very interesting connection was discovered. When the maternal grandmother lived in the same household or in the immediate vicinity and was thus able to maintain regular contact with her grandchildren, there were more offspring in the family than when this was not the case. If the mother was able to give her small children to the grandmother, she was more likely to have another child. It was found that the presence of the grandmother can significantly increase the survival rate of the grandchildren. At that time, the infant mortality rate was extremely high. However, if there was a maternal grandmother, the survival rate of children between the ages of two and five increased by 30%. The further away the grandmother lived from her daughter, the smaller the so-called grandmother effect. It means 0.6 fewer children per woman per 100 km. An interesting fact is that this granny effect seems to only work on the maternal line.

This grandmother effect has also been observed and described in the animal kingdom. Two species of mammals that live in a matriarchal structure were examined more closely. These two species include elephants and Orcas. Orca females enter menopause around the age of 40. It was concluded that if the grandmother is no longer able to reproduce, she needs less for her own needs. She no longer needs as much food for her own milk production or to care for her own calves. The grandma effect is particularly evident in this case when the food, for example salmon, is not available in abundance. She shares her food with other group members. With Orcas, it is a grandmother who leads the hunt. She also passes on her experience to the other group members. In addition, the Orca grandma babysits her grandchildren. Next to humans, killer whales are the creatures that have the longest post-productive lifespan in the animal kingdom.

In our conversation, the question arose whether this grandmother effect also applies to Pilot whales. This is a very interesting consideration. Like Orcas, Pilot whales are also organized matriarchal. Here, too, the female animal enters the menopause quite early, namely at around 35 years of age. So the assumption could be obvious that this question could possibly be answered in the affirmative. However, studies on this are not available.

Today we had wonderful encounters with Short-finned pilot whales (Globicephala macrorhynchus) and Bottlenose dolphins (Tursiops truncatus). In the afternoon we were surprised with special visitors, the Rough-toothed dolphins (Steno bredanensis). They were, as usual, very cuddly. Our guests were thrilled.