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By Deane Morrison
We humans have a strong urge to reproduce, but if the environment steers us into putting off having children, we may be rewarded with both longer life and a bigger genetic footprint in future generations.
A new University of Minnesota study reveals what may be a major force in shaping the evolution of most living things, including humans. Harnessing this natural effect could open the door to new means of delaying reproduction while promoting longer, healthier lives.
The work, led by ecology, evolution and behavior graduate student Will Ratcliff, was published in the Public Library of Science.
The basic idea is simple. When environmental cues like food shortages signal that the population is about to shrink, individuals who can afford to wait until this has happened should do so; then their offspring, when they come, will represent a bigger fraction of the gene pool.
"When the population is declining, future kids make a greater splash in the gene pool than current kids," Ratcliff said. "If there are tradeoffs between reproducing now versus later, delaying can be a good idea even if it reduces the number of kids you have during your lifetime."
Conversely, if hard times turn to good times and the population is about to boom, it's better to get those kids out there sooner, while the population is still small.
Over evolutionary history, early reproduction has reduced life expectancy due to the risk of complications in pregnancy, death in childbirth, damaging fights for mates or social status, and the demands of caring for and protecting offspring, Ratcliff said. Though lessened for modern humans, these risks shaped the evolution of our responses to stress.
For example, in some parts of Africa that suffer chronic food shortages – an environmental signal that the population will decline – girls experience their first menstrual period at later ages.
"Delaying reproduction to age 16 instead of 12 can really increase your chances, and your offspring's chances, of survival because having children very young is fraught with risk," Ratcliff said.
But in Western countries where girls have been getting richer food in recent years, the age of menarche has been receding. Rich food is an environmental signal that the population is poised to rise, and so the age of fertility has dropped.
Besides food availability, the environment may signal an imminent population decline chemically. Many food plants produce toxins that tend to depress reproduction and extend the lifespan. Humans may have eaten more of such plants when meat and other rich foods were relatively scarce, a sign that a population is facing a decline.
"A lot of these toxins extend life in ways that mimic dietary restrictions and have been shown to extend life in mice, fruit flies, roundworms, and yeast," Ratcliff said. "The whole point is that if a population is headed downhill, an individual who trades early reproduction for longevity can come out ahead."
One mechanism may involve testosterone, which suppresses the immune system, R. Ford Denison said, Ratcliff's faculty adviser and adjunct professor in the University's College of Biological Sciences. Thus, a toxin or other cue that reduces testosterone levels would tend to extend life as well as dampen reproductive behavior. Someday, the researchers say, harbingers of population decline may result in new drugs or lifestyle changes that lead to delayed reproduction and, potentially, longer and healthier lives.
What counts are the message organisms are getting from the environment, not necessarily the actual situation, the researchers said. For example, while the stress of regular fasting can delay reproduction and extend life, animal experiments have shown that the mere odor of food can reverse this effect.
By William Roberts, M.D., M.S.
Dehydration and sports. We hear about the issue all the time, but how much do you know?
Anytime a person exercises he generates heat, which is a byproduct of muscle work. This raises body temperatures, which triggers the brain to tell the skin to sweat. Sweat is mostly water, so it needs to be replaced in order for an athlete to maintain normal body function.
Athletes most at risk for dehydration are those who perform in hot conditions and those who wear a lot of equipment. Football players are at the greatest risk in Minnesota, since these student athletes are required to practice for five days without equipment in order to get acclimated to the heat.
So how much water do you need in order to stay properly hydrated? Athletes sweat at different rates, so it’s hard pinpoint an exact amount. But generally, for every pound of body weight lost during physical activity, the athlete should drink one-and-a-half pints of water. Therefore, if you lose two pounds, drink three pints to regain hydration.
Staying hydrated is fairly easy to do. If you’re thirsty, your body probably needs water. If you’re not thirsty, your body is probably all right. An easy way to keep an eye on your hydration level is to monitor your urine. Urine should be the color of light lemonade. Unlike what you may hear from coaches, urine should not be clear. If it is, you run the risk of hyponatremia, which means there is too much water in your body. On the other hand, urine should not be too dark. If it looks like apple juice, start drinking water because you’re most likely dehydrated.
Oftentimes I see athletes eating orange slices in between periods of a hockey game or at halftime of a soccer match. While intentions of replenishing one’s body with nutrients during intense physical activity are correct, the best way to do this is with sports drinks. Your body does need the sugar and sodium, but receiving these through food sources makes your body work harder in order to break down the nutrients. Sports drinks provide nutrients — and in liquid form.
The time to bring food into physical activity is directly following a demanding workout or competition. The sooner you can get calories into your body, the better. Consume a large amount of calories immediately after your workout, and an hour or two later, have a normal meal. This will help your muscles recover and better prepare your body for competition the next day.
While the temperatures continue to rise this summer, make sure you’re staying hydrated and fueled. After all, unlike most things in athletics, these are things you can control.
William Roberts, M.D., M.S., is professor of family medicine and community health at the University of Minnesota. Areas of specialties include ice hockey injuries, marathon injuries and exertional heat stroke. For more health-related information, go to http://www.healthtalk.umn.edu.
By Shirley J. Anderson-Porisch,
Have a son or daughter going off to college? You can help them make good decisions with their money. When asked how to make good decisions with money, I start by taking a look at spending – and now is the time to talk with them about money management skills.
Even though we may not always consciously ask ourselves questions about money, every spending decision involves questions: What are the options? What are the pros and cons of each option? Which option will I choose? Will I choose that option in the future? Asking and answering these questions when making a decision should result in a positive solution.
College students who make decisions with money by asking themselves questions and following a plan will likely be able to stay in control of their finances. The plan should show available money for spending or income, and compare that to expenses. By making good decisions about expenses, income will remain balanced.
To illustrate that point, let’s look at some common spending scenarios for a college student.
A common source of college student income is a job. If a student works 20 hours per week at $8 per hour, the net monthly income is $480. Their expenses may include $100 for gas, $80 for car insurance, $75 for a cell phone bill, $100 for clothes and personal care, and $125 for various entertainment costs. Spending at these levels would keep the student on track with their $480 of income.
So what if a student’s plan for spending decisions is out of balance? Suggest they work a few more hours for more income or finding a way to reduce their spending.
Increasing income is not always the solution – more income usually means more spending.
Any college student will do well with their spending decisions if they:
• Plan all spending: track it, record it and monitor it.
• Spend wisely: pay on time, stay within limits and make the most of available money.
• Organize spending information: open mail daily and file it safely for timely retrieval.
Planning for spending decisions during the college years may well last a lifetime.
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Shirley Anderson-Porisch works as a family resource management Extension educator at the University of Minnesota and is an expert in family finance. She has long been a media contributor and is an accredited financial counselor.
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