Scientists say that Darwinian ‘survival-of-the-fittest’ laws continue to affect human evolution even in the modern world.

New research, recently published in the Proceedings of the National Academy of Sciences, finds that despite technological and medical advancement and an increase prevalence of monogamy, natural and sexual selection is still significantly shaping human evolution.

Researchers looked at church records of about of 5,923 people who lived in four different farming or fishing villages in Finland born between 1760 and 1849, a time period where agriculture was relatively well established and society had strict rules against divorce and extramarital affairs. 

Researchers studied economic status, births, deaths and marriages to examine four key aspects of life that affect survival and reproduction, like which individuals lived beyond age 15, who got married or stayed single, how many marriages each individual had (at the time a second marriage was only possible if a spouse died), and how many children were born in each marriage. 

The findings show that in all four villages natural selection was apparent and similar to selection seen in the wild, as almost half of the people who had died before age 15 had traits that were not favored by natural selection, like susceptibility to disease, and therefore none of their genes were passed on to the next generation. 

Researchers found that a fifth of the individuals who survived past childhood but did not get married and had no children also had traits that prevented them from passing on their genes. 

Wealthy Finns who had land were also just as susceptible to natural selection pressures as their poorer landless counterparts, suggesting that “wealth did not buffer the environment enough to prevent natural selection from culling or favoring individuals,” according to Science Magazine. 

“We have shown advances have not challenged the fact that our species is still evolving, just like all the other species 'in the wild'. It is a common misunderstanding that evolution took place a long time ago, and that to understand ourselves we must look back to the hunter-gatherer days of humans," co-author Dr Virpi Lummaa, from the University of Sheffield's department of animal and plant sciences said in a statement.

"We have shown significant selection has been taking place in very recent populations, and likely still occurs, so humans continue to be affected by both natural and sexual selection,” Lummaa said.  “Although the specific pressures, the factors making some individuals able to survive better, or have better success at finding partners and produce more kids, have changed across time and differ in different populations."

However researchers noted that like most animal species, men and women are not equal when it comes to natural selection because men who were able to attract new mates had more offspring. Researchers found that on average men with one partner were able to have about five children, but with four partners men had an average of 7.5 offspring. 

Researchers suggested that the sexual selection process was more important in men than in women in terms of passing down genes not only because mating with more partners increases the chance of reproductive success for a man and not for a women, but also because men tended to remarry younger women with better child-bearing potential.

Therefore, co-author Dr Alexandre Courtiol, from the Wissenschaftskolleg Institute for Advanced Study in Berlin, Germany, said that the characteristics or traits that increase mating success of men, like attractiveness, are likely to evolve more rapidly than those that increase the mating success of women, according to a statement.

“Surprisingly, however, selection affected wealthy and poor people in the society to the same extent," he added.

Researchers could not determine which traits were being selected in the Finnish populations examined, but they found that the range of the number of offspring for individuals looked at ranged from zero to 17, suggesting that there was a large opportunity for natural selection to occur. 

Stephen Stearns, an evolutionary biologist at Yale University, told Science Magazine that while the importance of sexual selection has been widely accepted in birds and fish, the latest research “is the first time that sexual selection has been so well documented in humans.” 

Stearns added that the latest findings provide “additional, conformational evidence” for showing the existence of occurring natural selection.

Courtiol is not sure how strong natural selection is today, especially in the developed world, but he believes that his latest research showed ample evidence that even as recently as 200 years ago, Darwinian laws still played a role in shaping humans as a species, and he noted that biological as well as cultural processes should both be considered in understanding how humans have evolved through time.