BMC Biol. 2018 May 15;16(1):53. doi: 10.1186/s12915-018-0519-2.

Caring for parents: an evolutionary rationale.

Garay J1,2, Számadó S3,2, Varga Z4, Szathmáry E5,6.

Author information

1

MTA-ELTE Theoretical Biology and Evolutionary Ecology Research Group and Department of Plant Systematics, Ecology and Theoretical Biology, L. Eötvös University, Pázmány P. sétány 1/C, Budapest, H-1117, Hungary.

2

MTA Centre for Ecological Research, Evolutionary Systems Research Group, Klebelsberg Kuno utca 3, Tihany, 8237, Hungary.

3

RECENS "Lendület" Research Group, MTA Centre for Social Science, Tóth Kálmán u. 4, Budapest, H-1097, Hungary.

4

Department of Mathematics, Szent István University, Páter K. u. 1, Gödöllő, H-2103, Hungary.

5

Parmenides Center for the Conceptual Foundations of Science, Kirchplatz 1, 82049, Pullach/Munich, Germany. szathmary.eors@gmail.com.

6

MTA Centre for Ecological Research, Evolutionary Systems Research Group, Klebelsberg Kuno utca 3, Tihany, 8237, Hungary. szathmary.eors@gmail.com.

Abstract

BACKGROUND:

The evolutionary roots of human moral behavior are a key precondition to understanding human nature. Investigations usually start with a social dilemma and end up with a norm that can provide some insight into the origin of morality. We take the opposite direction by investigating whether the cultural norm that promotes helping parents and which is respected in different variants across cultures and is codified in several religions can spread through Darwinian competition.

RESULTS:

We show with a novel demographic model that the biological rule "During your reproductive period, give some of your resources to your post-fertile parents" will spread even if the cost of support given to post-fertile grandmothers considerably decreases the demographic parameters of fertile parents but radically increases the survival rate of grandchildren. The teaching of vital cultural content is likely to have been critical in making grandparental service valuable. We name this the Fifth Rule, after the Fifth Commandment that codifies such behaviors in Christianity.

CONCLUSIONS:

Selection for such behavior may have produced an innate moral tendency to honor parents even in situations, such as those experienced today, when the quantitative conditions would not necessarily favor the maintenance of this trait.