Tag Archives: sexual selection

Not so picky and coy after all: Female animals also have mating contests. They’re just more subtle than males

Sage-grouse on lek site in Central Oregon. Credit: NRCS Oregon, Flickr.

Men chase and women choose. This old-fashioned perspective on dating is also surprisingly prevalent among scientists studying mating dynamics shaped by sexual selection, wherein male animals are seen as more expendable and have to compete for the attention of picky females. But a new study shines light on the often-overlooked female competition for access to quality male mates, showing that sexual selection in females is actually the norm rather than the exception.

Victorian-era sex stereotypes

Charles Darwin claimed that all living species were derived from common ancestors, proposing natural selection as the driving mechanism in his pivotal book On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life. Natural selection says that organisms better adapted to their environment would benefit from higher rates of survival than those less equipped to do so, and would thus be more likely to pass on copies of their genes.

Darwin noted, however, that some elaborate traits had no apparent adaptive purpose and clearly did not aid survival (and in some cases jeopardized it by attracting predators) but rather served a sexual purpose. The male peacock with its extravagant plumage is an often-cited example of this effect. These traits could evolve if they are sexually selected, hence the name sexual selection, which Darwin explored at length in his follow-up book, The Descent of Man.

Sexual selection operates through two mechanisms: intrasexual selection, which refers to competition between members of the same sex (usually males) for access to mates, and intersexual selection, where members of one sex (usually females) choose members of the opposite sex. 

In a new study, a team of researchers led by Salomé Fromonteil of CNRS and the University of Rennes in France argues that the male-centered perspective on sexual selection is greatly exaggerated and has contributed to “a pervasive bias in research agendas of behavioural ecologists and evolutionary biologists over the last decades.

“Despite an increased awareness that females also compete for mating partners, we still tend to consider sexual selection in females a rare peculiarity,” the researchers wrote in a new study that appeared in the preprint server biorxiv.org.

In the 19th-century, Darwin wrote in his original conception of sexual selection that “with almost all animals, in which the sexes are separate, there is a constantly recurrent struggle between the males for the possession of the females” and that “the female […], with the rarest exception, is less eager than the male […,] she is coy and may often be seen endeavouring for a long time to escape from the male.”

This Victorian-era assertion has proven remarkably resilient, largely because there is some truth to it. In 2016, Tim Janicke, an evolutionary biologist at the University of Montpellier in France and co-author of the new study, measured the strength of sexual selection acting upon a variety of animal species and found that males experience a higher degree of sexual selection than females do.

However, the male side of sexual selection is greatly inflated compared to the female side, the researchers argue. For instance, studies exploring aspects of sexual selection on males outnumber those examining female competition for mates and male choice by a factor of ten to one, despite the fact that there are numerous instances of female intrasexual selection in the animal kingdom.

When females compete for males’ attention

Seahorses mating, taken at Seahorse World in Beauty Point, Tasmania. Credit: Flickr, John Dalton.

The clearest examples can be found in so-called sex-role reversed species in which the females actively compete for males and are the more ornamented sex. These include pipefishes and seahorses, in which fertilization takes place inside the brood pouch of the male until the young are ready to hatch, and this male will provide all parental care. In such species, males are a limited resource for which females have to compete, which leads to selection for ornaments favored by males in both pre- and post-copulatory mate choice.

However, nature doesn’t have to be flipped on its head in order to see sexual selection operating in females. Even in species with conventional sex roles where male ornamentation and extravagant courtship behaviors are selected for, you can still see female competition for high-quality males. For instance, female wattled jacanas (Jacana jacana) are known to aggressively fight for control over territory in order to monopolize multiple mates. Meanwhile, dung beetle females have evolved small horns that they sometimes use to battle other females in contests over access to mates. In Black grouse (Tetrao tetrix), both males and females compete for mates in elaborate courtship displayed arenas called leks.

“Consequently, sexual selection in females might actually be an omnipresent phenomenon in animals but operating less intensely and more subtly compared to males, which can make it more difficult to detect,” the researchers wrote.

In their new investigation, Janicke and Fromonteil investigate the published literature reporting evidence of sexual selection in females from 72 species. Particularly, the researchers measured and compared the Bateman gradient, a measure of the fitness benefit of mating, named after 20th-century British geneticist Angus John Bateman.

Bateman’s work showed that males produce sperm at a low energy cost, whereas females have a relatively much higher investment in far fewer eggs. This energy imbalance in gamete investment, Bateman argued, drives competing strategies in males and females. Males are thus incentivized to spread their sperm to as many mates as possible and to compete with other males for access to mating partners, while females are incentivized to be more choosy.

Sex is costly for females but the worst outcome is no sex at all

The Bateman gradient is a measure of the benefit of having multiple mating partners. The steeper the curve of the Bateman gradient, the greater the fitness benefit a male or female gains from mating more.

Although these gradients varied wildly among the species included in the meta-analysis, the researchers found that females from species that had access to many partners had higher Bateman gradient values than females of species that tended to mostly mate with one male at a time.

In effect, this means that, just like males, females also gain a fitness boost from access to multiple males, which naturally opens the door for sexual selection. In fact, the study’s authors claim that sexual selection in females is the norm rather than the exception across the animal tree of life.

“Specifically, our results document that females – just as widely assumed for males – typically benefit from having more than one mating partner. As a consequence, selection is also expected to favour the evolution of female traits that promote the acquisition of mating partners. However, given the previously documented higher benefit of mating in males, sexual selection on females may often operate more hiddenly leading to the evolution of less conspicuous ornaments and armaments compared to males,” they wrote.

While the relative difference in gamete cost between the sexes likely drives important behavioral changes in their mating strategies, the researchers argue that reproductive success may sometimes be maximized when mating with multiple mates or, at the very least, having additional mating episodes.

“Collectively, our study contributes to a more nuanced view on sexual selection and sex differences in general. Darwinian sex roles may predominate the animal tree of life in the sense that sexual selection is typically stronger on males compared to females but our meta-analysis questions the view that females are typically coy and passive. Sexual selection on females should not be considered a rare phenomenon but instead be acknowledged as widespread across animals,” the researchers concluded.

Why do men have beards? An inquiry from an evolutionary biology perspective

Credit: Pixabay.

One of the most easily recognizable features of sexual dimorphism in humans is the fact that males grow beards whereas women don’t. But what is the point of having a beard in the first place, evolutionary-speaking?

Do beards make men more attractive?

Whenever there are important physiological differences between males and females of a species, these features are more often than not due to the evolutionary pressure of sexual selection — the process that favors traits that promote mating opportunities.

Charles Darwin proposed the concept of sexual selection 150 years ago in On the Origin of Species by Means of Natural Selection, but his definitive work on sexual selection was undoubtedly covered in ones of his lesser-known works: The Descent of Man, and Selection in Relation to Sex, which was published in 1871. Although Darwin wrote extensively about sexual selection and offered ample evidence to support his thesis, this simple quote from the book illustrates the concept quite clearly:

“We are, however, here concerned only with that kind of selection, which I have called sexual selection. This depends on the advantage which certain individuals have over other individuals of the same sex and species, in exclusive relation to reproduction.”

Essentially, Darwin argued that sexual selection drove variation in traits such as skin and hair color, and also shaped many differences between men and women. According to Darwin, such traits help, not with the struggle for survival (natural selection), but with the struggle for reproduction.

However, determining the effects of sexual selection in humans is very tricky because our behavior is also largely driven by culture. It may be difficult to identify a human complex behavior that is completely independent of culture or social learning. For instance, we dress in fashionable clothes to attract the opposite sex — and fashion always changes with the times and varies depending on the geographical location. Footbinding in ancient China and neck rings in the Kayan are some extreme examples of such behavior.

So what does all of this have to do with beards? Being a defining feature of men, it stands to reason that beards evolved to attract mates. However, studies have been rather inconclusive in this respect.

It’s not the beard, bro. Credit: Pixabay.

One 2013 study found that “women judged faces with heavy stubble as most attractive and heavy beards, light stubble and clean-shaven faces as similarly less attractive.” However, a 1996 study reached the opposite conclusion, finding that men with “facial hair were perceived as more aggressive, less appeasing, less attractive, older, and lower on social maturity than clean-shaven faces.”

To complicate things even further, research suggests that in times when beards are fashionable, being clean-shaven is more attractive, while if there are many clean-shaven men, beards become more attractive simply by contrast.

Some women really like beards, while others can’t stand them. There’s no universal preference for beards across the board.

The lack of consistent evidence and the fact that most studies are performed with Westerner participants makes a poor case that men’s beards serve to attract females. However, we’re not out of sexual selection territory yet.

Beards as a signal of dominance for other men rather than an attraction cue for women

Traits favored by sexual selection do not necessarily serve to attract, they can also improve reproductive outcomes by making men appear more dominant, hence more able to fend off competition for mates.

Studies suggest that men with beards are perceived as older, stronger, and more aggressive than those that are clear-shaven.

Credit: Pixabay.

One interesting study that assessed British facial hair styles between 1842 and 1971 found that beards and moustaches became more fashionable during times when there was a great proportion of single men competing for fewer women.

A 2015 study, which was published in the journal Behavioral Ecology, found that perceptions of men’s dominance increased with features of masculinity (lower-pitched voices and greater beard growth). Beards didn’t appear to affect a man’s attractiveness rating.

“Together, these results suggest that the optimal level of physical masculinity might differ depending on whether the outcome is social dominance or mate attraction. These dual selection pressures might maintain some of the documented variability in male physical and behavioral masculinity that we see today,” the authors wrote.

Beards to soften the punch?

Credit: Pixabay.

Aside from enhancing traits of dominance (and providing the perfect breeding grounds for bacteria and other germs), beards may also serve a very practical purpose.

A recent study, which was published in April 2020 in the journal Integrative Organismal Biology, suggests that growing a thick beard offers protection for the human jaw from the impact of blunt force.

Previous research suggested that human hands evolved to be used as weapons and the human face is naturally developed to withstand blunt force.

The new study suggests that the beard can also offer men an edge during physical confrontations with other males. The researchers covered a human skull with fiber epoxy composite and grafted a beard made of untrimmed sheepskin.

Their trials found that the faux beard absorbed 37% more energy than hairless models. What’s more, beard-covered skulls broke bones only 45% of the time, compared to hair-free skulls that broke almost all of the time.

“These differences were due in part to a longer time frame of force delivery in the furred samples. These data support the hypothesis that human beards protect vulnerable regions of the facial skeleton from damaging strikes,” the authors wrote.

Bottom line: it’s highly unlikely that beards are some fluke of evolution. Instead, they’re likely the result of evolutionary pressures meant to enforce dominance hierarchies, perhaps enabling some men to intimidate competitors for mates. They may also aid in physical confrontations with other men by softening the impact of blunt force. In the end, unfortunately (or maybe fortunately for you), there is limited evidence that beards make men more attractive.

When it comes to narwhal sexual selection, tusk size matters

The only thing cuter than this male (with tusk) and female is the fact that a group of narwhals is technically called a ‘blessing’. Credit: Carsten Egevang, Greenland Institute of Natural Resources.

Reproduction is essential to the continuation of any species and organisms have developed all sorts of strategies — some more bizarre than others — under the pressure of sexual selection.

Peacocks are usually the most common example, with their extravagant plumage meant to attract females, at the expense of being a clear target for predators. Other animals attract mates by growing disproportionately large body parts that signal power. Elks have antlers, crayfish use claws, and the narwhal woos ladies with their powerful tusks.

“Broadly, I’m interested in sexual selection, which is responsible for creating some of the craziest traits in biology. As an evolutionary biologist, I try to understand why some animals have these bizarre traits, and why some don’t,” said Zackary Graham, a doctoral student at Arizona State University’s School of Life Sciences.

“One way we try to understand these traits is by looking at the morphology, or the size and shape of them. I immediately became obsessed with trying to think of some interesting animals to study. I was Googling everything; maybe I can find a dinosaur in a museum. Eventually, I found the narwhal tusk.”

Narwhals have tusks protruding out of their foreheads that can grow more than 8-feet-long (2.5 meters) in some of the most gifted individuals. These aren’t horns but rather modified teeth, similarly to those sported by walruses and elephants. Their spiral pattern also gives them an almost mythical appearance, due to which they are sometimes referred to as the “unicorns of the sea”.

Big tusks: an honest signal to potential mates

Narwhals are rather elusive creatures since they spend most of their lives under the thick Arctic ice. This has led to many speculations as to their main purpose. The tusks might be used for fighting, hunting, or — as this latest study suggests — attracting mates.

Graham has a lot of experience studying sexual selection in a variety of species. His Ph.D. thesis, for instance, was focused on the crayfish whose massive claws, known as chelae, often make up 35–50% of their total dry weight. Males with large chelae were more likely to survive predation, occupy positions of dominance, and copulate with females than males with small chelae.

The researchers looked at the relationship between tusk size and narwhal body size in 245 adults that were documented by previous studies over the course of 35 years.

Sexually selected traits — by which I mean those favored for their reproductive value — are often characterized by disproportional growth. Very large individuals will most often have larger than expected sexually selected traits (a large elk has even larger antlers compared to smaller individuals).

The tusk grows out in a spiral pattern, giving the appearance of a sea-dwelling unicorn. Credit: Carsten Egevang, Greenland Institute of Natural Resources.

Graham and colleagues studied narwhal males of the same age, focusing on the growth (or scaling) of the tusk in relationship with body size. The tusk scaling was then compared to the scaling relationship between body size and a trait that is unlikely to have any sexual function, such as their tail (called a fluke).

“We also predicted that if the narwhal tusk is sexually selected, we expect greater variation in tusk length compared to the variation in fluke width,” said Graham. 

Some male tusks were found to have as much as a 4-fold variation in length, despite having the same body size. In contrast, the fluke hardly varied at all, ranging in size from 1.5-feet to 3-feet long (2-fold variation) within individuals of the same body size. There was also evidence of disproportional growth in the tusk compared to the fluke.

This is the best evidence to date that narwhal tusks are sexually selected.

“By combining our results on tusk scaling with known material properties of the tusk, we suggest that the narwhal tusk is a sexually selected signal that is used during the male-male tusking contests,” said Graham. “The information that the tusk communicates is simple: “I am bigger than you.”

Many sexually selected traits, such as the narwhal’s tusk, require extra resources to foster their development — things like nutrients and body conditions. As such, the biggest, strongest, and most dominant individuals usually afford the resources and energy needed to produce extremely large sexually selected traits. So, a larger tusk compared to other individuals sends an honest signal of sexual quality to both females and other males (their competition).

This isn’t the last word on the matter. Graham hopes that in the future he will be able to use drones and submersible robots in order to record the behavior of elusive narwhals in their natural habitat, deep below the Arctic sea.

“Overall, our evidence supports the hypothesis that the tusk functions both as a sexually selected weapon and sexually selected signal during male-male contests,” said Graham. “However, further evaluations of the narwhal’s ecology are warranted.”

The findings were reported in the journal Biology Letters. Colleagues from the LUTA do Departamento de Ecologia e Biologia Evolutiva, UNIFESP, Brazil and the Greenland Institute of Natural Resources contributed to the narwhal dataset.

A male bird can either be handsome or a talented singer — but never both

Credit: Pixabay.

Male peacocks are famous for their flamboyant plumage, which doesn’t serve any purpose other than to attract a mate. It’s a prime example of sexual selection listed in every textbook on evolution. Funny thing is, for all the effort they put into their attire, peacocks are really lousy singers — and a new study found that they’re not alone. According to researchers at the University of Oxford birds who sing well have less striking plumage, and vice-versa.

You can’t have the best of both worlds

The researchers led by Christopher Cooney, an evolutionary biologist at Oxford’s Department of Zoology, compared the feather colors and songs of 518 species of birds.

The sex-differences in plumage coloration is a standard indicator of sexual selection, correlating with other indices such as testes size, the degree of polygyny (the practice of mating with multiple individuals), and extra-pair paternity (promiscuous mating behaviour in monogamous species). Another important indicator of sexual selection, particularly in birds, is represented by acoustic ornaments — the birdsong.

[panel style=”panel-info” title=”What is sexual selection?” footer=””]Charles Darwin proposed that all living species were derived from common ancestors, proposing natural selection as the driving mechanism. Natural selection simply states that organisms better adapted to their environment would benefit from higher rates of survival than those less well equipped to do so, and would thus be more likely to pass on copies of their genes.

Darwin noted, however, that some elaborate traits had no apparent adaptive purpose and clearly did not aid survival (and in some cases jeopardized it by attracting predators) but rather served a sexual purpose. These traits could evolve if they are sexually selected, hence the name sexual selection.

Sexual selection operates through two mechanisms: intrasexual selection, which refers to competition between members of the same sex (usually males) for access to mates, and intersexual selection, where members of one sex (usually females) choose members of the opposite sex. [/panel]

The analysis performed by the Oxford researchers had three parts. First, they analyzed published song recordings to estimate the extent of song divergence within species pairs. Second, they assessed the relationship — if there was one to begin with — between sexual dichromatism (sex differences in color of plumage among birds of the same species) and the degree of song divergence across pairs. Lastly, the researchers used statistical models to assess the relative association between dichromatism and song divergence in relation to other factors.

These findings suggest that birds where males showed off fancy plumage tended to have more monotonous songs. Conversely, bird species in which the male and female more closely resembled each other had livelier, longer songs.

The study published in the journal Royal Society Proceedings B seems to indicate that there’s an inherent trait between the two sexual selection traits. You can’t have both perhaps because each trait is costly. Also, perhaps it is pointless to expend energy when one of the traits is working just fine. Who needs to sing well when you look as fabulous as a male peacock?

 

Mandarin ducks, male (left) and female (right), illustrating the dramatic difference between sexes. Credit: Wikimedia Commons.

Male-female differences linked to risk of extinction, new study finds

A surprising new study suggests that the bigger the difference between sexes, the higher the odds that their species is heading for extinction.

Mandarin ducks, male (left) and female (right), illustrating the dramatic difference between sexes. Credit: Wikimedia Commons.

Mandarin ducks, male (left) and female (right), illustrating the dramatic difference between sexes. Credit: Wikimedia Commons.

Sexual dimorphism is the condition where the two sexes of the same species exhibit different characteristics beyond the differences in their sexual organs. For instance, many bird species show at least some dimorphism in color, with the female being cryptically colored to remain concealed in the nest while the more-colorful male uses it flashy plumage in displays of courtship and territorial behaviors. In some species, there is also a size mismatch between the sexes. For instance, for most mammals, the male is larger than the female, but for other animals, such as some spiders, the female is larger than the male. Homo sapiens has a low level of sexual dimorphism compared with many other species — and the similarity in the sizes of male and female human beings is a good example of how nature often does not make clear divisions.

There are various reasons why sexual dimorphism exists in the first place, which is the product of evolution by natural selection. For instance, a male bird’s bright coloration signals to the female that he is fit, healthy and a good choice to father her chicks. For deer, a male’s sexually dimorphic weapon — his antlers — is used to fight each other to establish breeding rights. Female insects are often larger than males, in order to lay more eggs.

The reproductive success of an organism is often more important than its long-term survival, which is why scientists have always debated whether sexual dimorphism is actually good or bad, as a whole, for a species. A peacock’s bright, bombastic plumage, for instance, can attract a worthy mate — but also a predator.

Researchers at the Smithsonian Institution compared tiny crustaceans called ostracods, which lived throughout the Late Cretaceous, from 66 to 84 million years ago. The team found that among the 93 ostracod species, it was those species with the greatest sex differences that were also the likeliest to go extinct — up to ten times likelier than species with less pronounced sexual dimorphism.

Female ostracodes of the species Veenia ponderos. Credit: Gene Hunt.

Male ostracodes of the species Veenia ponderosa, Credit: Gene Hunt.

Male ostracodes of the species Veenia ponderosa, Credit: Gene Hunt.

It’s not clear yet whether these results generally apply to other species or genera for that matter — but it might very well be true. Previous studies on birds and mammals found similar results, concluding that sexual selection increases the risk of extinction. What’s more, the general pattern seems to be the same: the male of many species invests considerable resources to attract or compete for mates.

The results are important for conservationism. If sexual dimorphism is truly a significant risk factor, then we have to take it into account when planning for shifting conditions.

In the future, the researchers plan on studying sexual dimorphism in ostracodes in the next geological interval, the Paleocene. The present study ends right before the extinction event that wiped out the dinosaurs, and the authors are interested in learning if the extinction triggered any shift in dimorphism.

Findings appeared in the journal Nature.

Ladybugs.

If you like having sex, you should thank pathogens for making it possible

The arms race between pathogens and the organisms they infect may be the fundamental reason why animals have taken to having sex and then stuck with it, a new paper reports.

So why do we have sex? Well, it’s obvious isn’t it — we do it to make more humans. But there is a small chink in that explanation, something which has been bothering evolutionary geneticists for about as long there have been any around: sexual reproduction is hard work, whereas asexual reproduction is easy and much more efficient — so why bother with it?

Ladybugs.

Image via Pixabay.

That’s something we’ve all asked ourselves at one point or another but Dr. Jack da Silva and James Galbraith from the University of Adelaide have actually set out to get an answer. After using a computer model to simulate how the genomes of Caenorhabditis elegans (non-parasitic roundworms) shift throughout several generations, the duo suggests that sexual reproduction imposed itself because organisms needed to constantly adapt their genomes to fight off co-evolving pathogens.

“Asexual reproduction, such as laying unfertilised eggs or budding off a piece of yourself, is a much simpler way of reproducing,” says Dr da Silva, Senior Lecturer in the University of Adelaide’s School of Biological Sciences.

“It doesn’t require finding a mate, and the time and energy involved in that, nor the intricate and complicated genetics that come into play with sexual reproduction. It’s hard to understand why sex evolved at all.”

One decades-old theory has been attracting more attention recently, da Silva said. Known as the Hill-Robertson Interference, it holds that sexual reproduction evolved because it allows DNA recombination between mates, allowing offspring to ‘hoard’ more beneficial mutations. In the case of asexual reproduction, where there is no pooling of genes, beneficial mutations compete with each other and natural selection grinds down.

But de Silva says this theory doesn’t explain why sexual reproduction would be maintained in a stable, well-adapted population — where maintaining the status quo makes more evolutionary sense.

 

“It is hard to imagine why this sort of natural selection should be ongoing, which would be required for sex to be favoured,” he says.

“Most mutations in an adapted population will be bad. For a mutation to be good for you, the environment needs to be changing fairly rapidly. There would need to be some strong ongoing selective force for sex to be favoured over asexual reproduction.”

The team’s suggestion is to bring another, less influential evolutionary theory into the mix. Known as the Red Queen theory, it holds that because bacteria, viruses, or parasites are continuously trying to adapt and overcome our natural or artificial defenses, our genomes are also trying to keep one step ahead by continuously mutating, becoming more resistant to them.

‘Good enough’ is better than ‘the best’

While we may be really well adapted to our environments, there’s a constant sort of biological arms race going on. Staying unpredictable — by having the ability to develop new mutations and pool them in offspring — thus becomes more advantageous than reaching a hypothetical ‘best-adapted’ genome and keeping with it.

So in the end, organisms may have chosen sexual reproduction over cloning because, although it’s harder and (on those lonely Saturday nights) more frustrating to pull off, it keeps us all similar but different enough so the germs can’t get us all in one shot. Which I feel is win for us.

“These two theories have been pushed around and analysed independently but we’ve brought them together,” says Dr da Silva. “Either on their own can’t explain sex, but looking at them together we’ve shown that the Red Queen dynamics of co-evolving pathogens produces that changing environment that makes sex advantageous through the simple genetic mechanism of the Hill-Robertson theory.”

“This is not a definitive test but it shows our model is consistent with the best experimental evidence that exists.”

The paper “Hill-Robertson Interference Maintained by Red Queen Dynamics Favours the Evolution of Sex” has been published in the Journal of Evolutionary Biology.

tall men

Why the Dutch are the tallest on the planet: sexual selection

European males are on average 11 centimeters taller now than they were in the 1870s, which is quite a lot by all means. Everybody makes fun of Napoleon for being short, but as a matter of fact even he was actually standing above average height. But even by European standards,the Dutch are really tall! What have they been eating that makes them this tall?  The average Dutchman now stands over six feet tall, and while the rest of the world seems to have stabilized their height,, they’re still riding a growing trendline. The answer may actually be evolutionary – the tall Dutchmen have more babies.

tall men

Image: Telegraph.co.uk

The average male height in the Netherlands has increased by 20 cm (eight inches) in the last 150 years, according to military records. By comparison, the height of the average American man has risen a mere six centimetres over the same period.

Dr. Gert Stulp, who unsurprisingly stands 6 feet and 7″ tall, studies why his fellow countrymen are the tallest on the planet. Not content with previous explanations like better food and access to medical care (it’s not quite exclusive to Holland), Stulp marched on an ambitious project in which he mined the LifeLines database. This is a sophisticated database with loads of records on Dutch families, including genetic and medical profiles. He focused on 42,612 men and women over age 45, and filtered the results by height and number of children given birth. This simple query reveals that taller men had more children.

Among those born in the early 1950s, for example, men who were 5 feet 6 inches had on average 2.15 children. Men who were 6 feet 1 inch had 2.39 children. And this trend has persisted for more than 35 years. This, of course, makes sense. Taller people make babies that grow to be tall and short people make short kids. It’s widely known that women favor taller partners, but this again is something that the whole world can relate to, not just the Netherlands. So, are Dutch women particularly biased? Are taller couples more sexually active, so they make more kids thus proliferating a skyhigh lineage? Clearly, this is far from settled. However, the evidence thus far does indeed seem to point towards a sexual selection explanation. Dr. Stulp and colleagues are now probing the records further analyzing the heights of parents and their children in the Netherlands.

“Height is very heritable – taller parents tend to have somewhat taller children than shorter parents,” Stulp said. “Because taller individuals would have more offspring in the next generation who would be taller, the average height in that generation would a bit taller on average than the preceding generation, if all else is equal.”

Stulp is also careful to highlight that by no means this is an absolute trend. For instance, he points out that shorter women and men of average height make the most productive pair as far as child bearing is concerned, hence height is definitely a cultural preference.

“There is much variation in what men and women want,” he said. “When it comes to choosing a mate, height tends to have (only) a small effect, which is not very surprising given the many other, more important, traits people value in their mate.”

Perhaps, the biggest takeaway we should all take from this is that evolution is a permanent work in progress. Even for us humans, it’s happening right now. With each generation, we adapt to an ever changing world. Our success depends on adapting at pace with the rate of change.

Humanity is still subjected to the natural process of evolution, despite advances

Evolution, in very loose lines, is defined as the process which allows a species to survive by passing on the differentiating traits most likely to help offspring adapt to the world through means of natural and sexual selection. Considering the world around us has been shaped so much by human hand, a lot of people have questioned whether the natural process of evolution still applies to modern day humans. A research carried out by scientists in Finland concludes that the human evolutionary process is still well in place, and that we don’t necessarily need to study early hunter-gatherer communities from 10,000 years ago to understand how the human species evolved, and subsequently survived.

The environment we live in today has been almost completely artifically revamped. Advances beginning with the agricultural and industrial revolutions, have lead to significant advances which have shaped our way of life and made us less subsceptible to external natural stimuli, like diseases, hunger, and so on – at least in the parts of the world we like to call “civilized”. To see if all these factors have affected the billion-year old process of evolution, scientist  in an international collaboration, analyzed church records of about 6,000 Finnish people born between 1760-1849 to determine whether the demographic, cultural, and technological changes of the agricultural revolution affected natural and sexual selection in our species. Finland was an ideal choice for study material, since the country’s church has kept strict records of births, deaths, marriages, and wealth status, which were kept for tax purposes for centuries.

This relatively extensive data set allowed the researchers to form patterns and compare them with other species. The scientists looked at four key aspects that the agrarian industry of the time affected people, namely survival to adulthood, access to mates, mating success and fertility per mate. The scientists found that the modern farmers and fishermen of Finland responded to evolution much in the same way other species did as well.

Project leader Virpi Lummaa, of the department of animal and plant sciences, says: “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.”

Lummaa adds: “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. 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.”

As for most animal species, the authors found that men and women are not equal concerning Darwinian selection.

Principal investigator Alexandre Courtiol, of the Wissenschftskolleg zu Berlin, adds: “Characteristics increasing the mating success of men are likely to evolve faster than those increasing the mating success of women. This is because mating with more partners was shown to increase reproductive success more in men than in women.

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

Understanding how natural and sexual selection still affects modern humans, in a time in which culture and science seeks to surpass our biological needs is extremely important to understanding ourselves in the first place, and hopefully predicting what shape society and the human species as a whole might take in the future. The present research offers some clues and glimpses that suggest the impact of natural and sexual selection which affects all living organism on Earth still very much applies to humans as well, and should not be underestimated.

“Most scientists studying human evolution focus only on our hunter-gatherer way of life 10,000 years ago, but we show that, albeit interesting, this will not give you a complete picture of the story — we also need to focus on how people were living until very recently, and probably even today,” Courtiol added.

“Extending our research toward modern days would be particularly interesting to understand how the current environment continues to shape humans,” Courtiol said. “This could be potentially of importance from a medical point of view, to understand, for instance, how quickly our immunity can respond to new major epidemics. One major obstacle is that we need reliable data at the level of individuals — number of offspring, number of partners, birth and death date — across the lifetime of all born individuals, and such datasets are rare because even many famous longitudinal studies are biased towards certain types of people or do not cover all necessary life events.”

Their findings are published in Proceedings of the National Academy of Sciences (PNAS).

source: Futurity