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Can we naturally select for sex?
I hope you are safe and well. We’ve had some interesting questions not related to coronavirus this week. Here’s what I’ve learned:
Sex of babies can’t be controlled by diet or timing
Numerous parenting internet sites claim all sorts of things for couples trying to have kids, like the claim that more acidic diets make having a girl more likely. Others claim couples can pre-determine their baby's sex by trying to conceive during certain times of the monthly cycle. Some even claim that avoiding dairy and eating bananas will help with the chances of getting a boy when trying to conceive. Are these methods of natural sex selection effective? asked one metafact user. We’ve had 3 top experts confirm it’s a myth.
There is no credible scientific evidence that having sex at different times of the cycle or that the acidic or alkaline environment of the reproductive tract have any significant effect on the sex of babies.
notes Professor George Seidel Jnr, a reproductive biologist from Colorado State University.
Dr Taylor Pini, also a reproductive biologist goes into more detail about the competition of sperm within the female reproductive tract in her answer here:
There is no evidence to suggest that the timing of intercourse has any impact on the sex of the resultant embryo. The sex of an embryo is determined by whether the sperm that achieves fertilization carries an X or Y chromosome. Eggs always carry an X chromosome, so an X sperm will create a female (XX) and a Y sperm will create a male (XY). Studies on sperm separated into X and Y bearing populations have shown little differences in important sperm performance characteristics (e.g. motility), suggesting that one would not "out compete" the other once in the female reproductive tract.
It’s easy for some people to get allured into the idea their baby was determined by these natural methods says Dr Karin Hammarberg, a fertility expert from Monash University:
There are no effective natural gender selection methods. The reason why people might believe in purported methods of natural gender selection is that the odds of having a baby with the desired sex is 50/50. So, if someone tries to time sex in a way they believe will favour one sex or another, and then have a baby with that sex, they are likely to attribute this to timing of sex. And if they have a baby of the opposite sex, they are unlikely to share the fact that the method didn't work!
Seems like the confirmation bias is at play here, like it is for many types of widely shared myths.
Water filters not needed at home say experts
Billions are spent each year on home water purifiers/filtration units. The premise is that municipal water being supplied to our houses require additional purification. Of course, water filtration companies want us to believe that tap water in the developed world needs extra treatment. Individual taste is an individual choice, but do we need extra filtration at home?
It all depends on where you live and the type of water reservoir says Professor Peter Scales, Water engineer from the University of Melbourne.
If we are talking about water from a reservoir in a place like Melbourne [Australia] in a highly protected catchment or high quality ground water, these only need one barrier – chlorine.
A ‘barrier’ is expert jargon for a treatment stage. Chlorine is often used as the primary disinfectant of barrier of choice to kill disease-causing bacteria, viruses, and parasites from the water supply. Cities who don’t have high-quality water catchments like in Melbourne need to add multiple ‘barriers’ to ensure clean water.
In somewhere like California, water quality is not quite as good as Melbourne but they have a 3-4 barrier system prior to the house. There is no need for further treatment although people still get sold lots of filters.
says Professor Scales.
Takehome is that for point of entry systems in houses, most of these don't need filtration systems, but people buy them and use them in any case.
There is also a healthy consensus suggesting that tap water (and it’s minerals) is actually better for you than purified water… The obvious caveat to all of this is when you live in rural areas or undeveloped countries with no treatment or poor quality catchments. In the developed world however, we are very very lucky "as 1 in 4 people [globally] still drink water that is not safe” says Professor Scales.
Notes, reminders and updates…
Beyond COVID-19: Our mission at Metafact is to find you trusted knowledge, vetted by verified experts in science & health. Since March, I have focussed primarily on COVID-19 related questions and will be publishing a review on this by the end of the month. Because of this focus and the lock-down our member-voted monthly reviews and audio versions have been delayed. But next month I plan to start moving beyond COVID-19, into the next three topics chosen by members: Vaping, Mental Health and Habits.
Sydney Launch: With members all around the world you may recall we had a San Francisco and London launch for Metafact late last year. I had finally organized the Sydney launch with Professor Ian Frazer (co-inventor of HPV vaccine) to happen this coming week. Well, that’s obviously on hold for a bit given COVID-19… We will be hosting the Sydney event when we can, hopefully later this year (if the curve remains flat). Thanks again for your support and patience during this time.
Voting has begun!
Voting has started again here, where you decide the topics for us to review. This month’s 5 review options are: coffee, green tea, whey protein, Vitamin D or creatine. It’s really important that we are investigating topics you care about: Go vote here!! If you want to add a topic to one of our polls - you can always send me a comment here.
Stay safe and may the facts be with you!
Ben McNeil, Founder of Metafact
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