# Mathematical Counseling for All Who Wonder Why Their Relationship Is Like a Sinus Wave (Science Daily)

ScienceDaily (Nov. 15, 2012) — Neuroinformaticians from Radboud University Nijmegen provide a mathematical model for efficient communication in relationships. Love affair dynamics can look like a sinus wave: a smooth repetitive oscillation of highs and lows. For some couples these waves grow out of control, leading to breakup, while for others they smooth into a state of peace and quietness. Natalia Bielczyk and her colleagues show that the ‘relationship-sinus’ depends on the time partners take to form their emotional reactions towards each other.

The publication in Applied Mathematics and Computation is now available online.

An example of a modeled relationship, in this case between Romeo (solid lines) and Juliet (dashed lines). The tau (τ) above the individual figures indicates the delay in reactivity. Delays that are too short (<0,83) cause instability, just like delays that are too long (>2,364). Delays in the range of 0,83-2,364 cause stability in Romeo and Juliet’s relationship. (Credit: Image courtesy of Radboud University Nijmegen)

In 1988, Steven Strogatz was the first to describe romantic relationships with mathematical dynamical systems. He constructed a two-dimensional model describing two hypothetical partners that interact emotionally. He used a well known example: the changes of Romeo’s and Juliet’s love (and hate) over time. His model became famous and inspired others to analyze (fictional) relationship case studies like Jack and Rose in the Titanic movie. However, the Strogatz model does not include delays in the partner’s responses to one another. Therefore it is only a good start for fruitful studies on human emotions and relationships.

That is why Natalia Bielczyk adjusted Strogatz to a more life-like model by considering the time necessary for processing and forming the complex emotions in relationships. The reactivity in the relationship model is based on four parameters: both partners have a personal history (their ‘past’), and a certain reactivity to their partner and his/her history. Depending on these parameters, different classes of relationships can be found: some seem doomed to break regardless of the partners promptness to one another while others are solid enough to always be stable. In the calculated models, stability occurs when both partners reach a stable level of satisfaction and the sinus wave disappears. The paper concludes that for a broad class of relationships, delays in reactivity can bring stability to couples that are originally unstable.

These results are pretty intuitive: too prompt or too delayed responses evoke trouble. Below a certain value, delays caused instability and above this value they caused stability, showing that some minimum level of sloth can be beneficial for a relationship. The fact that too fast emotional reactivity can lead to destabilization, shows that reflecting each other’s moods is not enough for a stable relationship: a certain time range is necessary for compound emotions to form. Summarized, the publication offers mathematical justification for intuitive phenomena in social psychology. Working on good communication, studying each other’s emotions and working out the right timing can improve your relationship, even without trying to change your partners traits (which is harder and takes more time).

Journal Reference:

1. Natalia Bielczyk, Marek Bodnar, Urszula Foryś. Delay can stabilize: Love affairs dynamicsApplied Mathematics and Computation, 2012; DOI: 10.1016/j.amc.2012.10.028

# When Leaving Your Wealth to Your Sister’s Sons Makes Sense (Science Daily)

ScienceDaily (Oct. 16, 2012) — To whom a man’s possessions go when he dies is both a matter of cultural norm and evolutionary advantage.

In most human societies, men pass on their worldly goods to their wife’s children. But in about 10 percent of societies, men inexplicably transfer their wealth to their sister’s sons — what’s called “mother’s brother-sister’s son” inheritance. A new study on this unusual form of matrilineal inheritance by Santa Fe Institute reseacher Laura Fortunato has produced insights into this practice.

Her findings appear October 17 in the online edition of Proceedings of the Royal Society B.

“Matrilineal inheritance is puzzling for anthropologists because it causes tension for a man caught between his sisters and wife,” explains Fortunato, who has used game theory to study mother’s brother-sister’s son inheritance. “From an evolutionary perspective it’s also puzzling because you expect an individual to invest in his closest relatives — usually the individual’s own children.”

For decades research on the practice of matrilineal inheritance focused on the probabilities of a man being the biological father of his wife’s children — probabilities that lie on a sliding scale depending on the rate of promiscuity or whether polyandrous marriage (when a woman takes two or more husbands) is practiced.

Of special interest has been the probability value below which man is more closely related to his sister’s children than to his wife’s children. Below this “paternity threshold” a man is better off investing in his sister’s offspring, who are sure to be blood relatives, than his own wife’s children.

In her work modeling the evolutionary payoffs of marriage and inheritance strategies, Fortunato looked beyond the paternity threshold to see, among other things, what payoffs there were for men and women in different marital situations — including polygamy.

“What emerges is quite interesting,” says Fortunato. “Where inheritance is matrilineal, a man with multiple wives ‘wins’ over a man with a single wife.” That’s because wives have brothers, and those brothers will pass on their wealth to the husband’s sons. So more wives means more brothers-in-laws to invest in your sons.

The model also shows an effect for women with multiple husbands. The husband of a woman with multiple husbands is unsure of his paternity, so he may be better off investing in his sister’s offspring.

“A woman does not benefit from multiple husbands where inheritance is matrilineal, however,” Fortunato explains, “because her husbands will invest in their sisters’ kids.” Family structure determines how societies handle relatedness and reproduction issues, Fortunato says. Understanding these practices and their evolutionary implications is a prerequisite for a theory of human behavior.

Journal Reference:

1. Dr Laura Fortunato. The evolution of matrilineal kinship organizationProceedings of the Royal Society B, October 17, 2012 DOI: 10.1098/rspb.2012.1926