New study finds the egg may actually 'choose' the sperm
Here's the first evidence to challenge the "fastest sperm" narrative.
If you've attended high school, you can probably remember filling in a Punnett square during a biology class. It was the simple diagram that could not only make you feel like a knowledgeable budding geneticist, but could also help you figure out the probability of your kids having blue eyes in the case the cute classmate you had a crush on agreed to live with you happily ever after.
Credit: Flickr / yourgenome
The Punnett Square is a visual representation of Gregor Mendel's laws of inheritance. They are three and they posit that 1) alternative forms of a gene (allele pairs) separate randomly during the production of an egg or sperm (gametes), so that each gamete only carries one form of the gene; 2) each pair of alleles segregates independently of other pairs during the formation of an egg or sperm; 3) the genotype of an individual is made of many alleles (after a random pairing of an egg and a sperm, each of which carries a random form of the gene), and the phenotype of an individual (the visible expression of the genotype) is determined by the dominant alleles and the environment.
What underlies all of Mendel's laws is the idea of randomness. Scientists believe that it is up to chance which sperm will fertilize an egg and which combinations of alleles the offspring would have. That is, of course, after the sperm has proven itself to be the strongest and most enduring swimmer of them all. But the point is, the egg has no say in this. It sits passively waiting to be fertilized.
This whole narrative, including Mendel's laws, may be about to change. Dr. Joseph H. Nadeau, principal scientist at the Pacific Northwest Research Institute, has found evidence that suggests eggs and sperm don't always combine randomly, but in fact the egg may choose which sperm to fertilize it. The findings have been published in Genetics.
Nadeau was tipped off by two experiments from his own lab which were supposed to produce specific predictable ratios of gene combinations in offspring (based on Mendel's laws), but they didn't. It actually turned out that certain pairings of genes are much more likely than others in the cases when the mother carries a particular gene.
Nadeau was exploring how the interactions between two genes (Apobec1 and Dnd1) affected the risks for testicular cancer in mice. He noticed a profound difference between the offspring of the mice in the cases when the mother carried a normal and mutated version of Dnd1 vs. when the father carried a normal and mutated version of the gene, and then the mice were bred with a partner who had a normal and mutated version of Apobec1. (Now is the time to bust out those Punnett chart skills.)
When the mother carried the two versions of Dnd1, the distribution of the genes in the offspring followed Mendel's laws but when the father did, the math went entirely off. Instead of finding the expected 75 percent of offspring to carry at least one of the mutant genes, they found that only 27 percent of the offspring did.
After eliminating other possible explanations for the unlikely ratios, like embryonic death, Nadeau concluded that fertilization must not have been random and there must be a mechanism that allows the egg to choose the sperm with the normal instead of the mutated gene. He calls it genetically biased fertilization.
“It's the gamete equivalent of choosing a partner," Nadeau says for Quanta Magazine. "We've been blinded by our preconceptions. It's a different way to think about fertilization with very different implications about the process of fertilization."
The mechanism of how the egg may decide which sperm to let fertilize it is still unclear. There probably are secreted and cell-surface factors in female reproductive organs that could control access of sperm to eggs based on their genetic content. Nevertheless these findings shed a new light on the female and her reproductive system, which as it turns out, has a much more active role in choosing a partner or a sperm cell and influencing the genetic composition of her offspring.
For more on the topic check out Quanta Magazine.
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Whether or not women think beards are sexy has to do with "moral disgust"
- A new study found that women perceive men with facial hair to be more attractive as well as physically and socially dominant.
- Women tend to associate more masculine faces with physical strength, social assertiveness, and formidability.
- Women who display higher levels of "moral disgust," or feelings of repugnance toward taboo behaviors, are more likely to prefer hairy faces.
Beards and perceptions of masculinity<img type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8yMjU5OTg0MC9vcmlnaW4uanBnIiwiZXhwaXJlc19hdCI6MTY0NzkxMjM3N30.cH-GqNwP5GVqvstgJWAhBPn1B_lYpVEAI0I7iax7EQw/img.jpg?width=1245&coordinates=0%2C1900%2C0%2C849&height=700" id="caae6" class="rm-shortcode" data-rm-shortcode-id="cb0a355a4e8e1899789bc45f3f7aef56" data-rm-shortcode-name="rebelmouse-image" />
Photo Credit: Wikimedia<p>The study used 919 American (mostly white) women ages 18-70 who rated 30 pictures of men they were shown with various stages of facial hair growth. The photographs depicted men with faces that had been digitally altered to look more feminine or more masculine, with a beard and without a beard. The women rated the men according to perceived attractiveness for long-term and short-term relationships. The study found that the more facial hair the men had, the higher the men were rated on their attractiveness, particularly for their suitability for a long-term relationship.</p><p>Part of this might be attributed to facial masculinity — i.e. protruding brow ridge, wide cheekbones, thick jawline, and deeply set narrow eyes — which conveys information to a woman about a man's underlying health and formidability. Women tend to associate more masculine faces with physical strength and social assertiveness. It can also indicate a man with a superior immune response. The researchers suggested that their findings favoring bearded men could be due to the fact that facial hair enhances the masculine facial features on a man's face, like creating the illusion of a thicker jaw line. This could communicate direct benefits to women like resources and protection that would enhance survival among mothers and their infants. In other words, while a beard doesn't mean superior genetics in and of itself, it might be a primitive, ornamental way of saying, "Hey girl, I'm a testosterone-fueled lean, mean, pathogen fighting machine." <br></p><p>It could also be that a beard becomes its own destiny. The researchers in this study cite prior research that found that by growing a beard, men felt more masculine and had higher levels of serum testosterone, which was linked to a higher level of social dominance. They also tended to subscribe to more old-school beliefs about gender roles in their relationships with women as compared to men with clean-shaven faces.<span></span><br></p>
What does disgust have to do with beard preference?<p>Obviously, not all women dig beards. The researchers were particularly interested in what traits make a women prefer bearded men over clean-shaven faces. They looked into several factors including a woman's disgust levels on various concepts, her desire to become pregnant, and her exposure to facial hair in her personal life. </p><p>According to the study, women who were not into facial hair were turned-off by potential parasites or other critters they imagined could be in the hair or skin. Women ranking high on this "ectoparasite disgust" scale might have viewed beards as a sign of poor grooming habits. However, women who ranked higher in levels of "pathogen" did find the bearded men to be desirable, possibly because they perceived beards as a signal of good health and immune function. An intriguing discovery in the study was links to morality. Women who displayed higher levels of "moral disgust," or feelings of repugnance toward taboo behaviors, were more likely to prefer hairy faces. The authors opined that this could reflect a link between beardedness, politically conservative outlooks, and traditional views regarding performances of masculinity in heterosexual relationships.</p>
Additional findings<img type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8yMjU5OTg1My9vcmlnaW4uZ2lmIiwiZXhwaXJlc19hdCI6MTYyNDI1NjUyOX0.P9B8WbmJR0q4nfzYZKbuNSA-2SAigVWJgrQE-_Gxlds/img.gif?width=980" id="49143" class="rm-shortcode" data-rm-shortcode-id="2ed3b1d6f20fc170bf2974646e565e8d" data-rm-shortcode-name="rebelmouse-image" />Giphy<p>The correlations that existed between married and single women's rating on the attractiveness of beards were not particularly clear, although the researchers noted that single and married women who wanted children tended to find beards more attractive than the women who didn't want children. They also found that women with bearded husbands found beards to be more attractive, which might indicate that social exposure to beards influences how desirable they are perceived of as being. Or it could be that men with wives who like beards grow beards.</p><p>It's important to note that culture plays a huge role in how attractive women perceive certain male characteristics as being. This study looked at a small, culturally specific group of American women, so no big, universal claims should be made about masculinity, facial hair, and male desirability to women. However, research like this is important in highlighting how human grooming decisions are driven by much more than fashion trends. Sociobiological, economic, and ecological factors all play a part in the way we choose to present ourselves.</p>
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