Why Love Appeared - Relations

When our ancestors began to enlarge their brains about 2 million years ago, new reasons arose for the further evolution of love. This is the sixth article in a series of stories about love by biologist Alexander Markov. Before that, we have already published other materials from this cycle: "Darling, I am dopaminergic motivated", or What is love, "Symptoms of love", "Prehistoric love", "How did love appear in the world", "Infantilism is a consequence of evolution?"

Large-headed babies are difficult to give birth, especially if you walk on two legs. The pelvic features required for bipedal walking conflict with features that would facilitate the birth of large-headed babies. Therefore, the babies of hominids began to be born very underdeveloped in comparison with the babies of other anthropoids (while their heads are not very large). Because of this, childhood was lengthened - the cubs now remained helpless much longer than other anthropoids. This means that more love and patience was required from the parents. Mothers had to love their offspring very much in order to nurse them so long and selflessly. And fathers also had to love their wife and children very much in order to support them for so long.

In human ancestors, a mutation in the prodynorphin gene was fixed, which may have influenced the reward sistem. A 68-nucleotide sequence - the regulatory region of the gene encoding the prodynorphin protein - in humans and other primates. The arrows show five mutations that are unique to humans.

(Rockman MV, Hahn MW, Soranzo N., Zimpich F., Goldstein DB, et al. (2005) Ancient and Recent Positive Selection Transformed Opioid cis-Regulation in Humans. PLoS Biol 3 (12).)

There are indirect genetic arguments for the fact that important changes have actually taken place in our emotional sphere, in the so-called reward system.

Показано, что люди отличаются от других обезьян несколькими мутациями в регуляторной области гена, кодирующего белок продинорфин. Продинорфин является предшественником (исходным материалом для производства) нескольких нейропептидов-эндорфинов, связанных с регуляцией эмоционального статуса и влияющих на поведение и формирование социальных связей. Эндорфины также называют эндогенными опиатами. Некоторые наркотики вызывают чувство эйфории как раз потому, что связываются с рецепторами эндорфинов.

Moreover, the coding part of the gene (the region in which the protein structure is encoded) in humans is the same as in other monkeys. Natural selection regularly screened out all the changes arising here. Therefore, both prodynorphin itself and the neuropeptides formed from it - endorphins - are the same in all monkeys, including humans. Only the regulatory region of the gene has changed - the region, the structure of which determines in what situations a given gene will turn on and off and with what intensity it will work (that is, ultimately, how many endorphins will be synthesized).

It turned out that replacing the "monkey" regulatory site with a "human" one leads to an increase in the synthesis of prodinorphin by nerve cells by about 20%. Maybe the evolutionary meaning of this genetic change was to increase the amount of endorphins produced by brain cells?

In principle, it can be assumed that humans are capable of experiencing stronger positive emotions than chimpanzees. Humans have to do a lot of things that chimpanzees won't do in life

For example, make serious sacrifices for your neighbor. Women of Homo sapiens experience absolutely non-monkey suffering during childbirth, and then, not like a monkey, they babysit helpless babies for a long time. This requires strong internal reinforcement, a powerful "internal reward system." After childbirth, by the way, there is a powerful release of endorphins.

Maybe our human feelings of delight, happiness, and, of course, love - are significantly superior in strength to similar experiences of chimpanzees? This is not excluded, although it is difficult to experimentally test this hypothesis. But the point is, most likely, not only that more endorphins were produced, but also that the synthesis of endorphins began to occur in response to some other stimuli. This could seriously change the motivation for actions, our desires and goals in life.

Photo: Lori Photo Bank / Image author