Why Do We Crave Junk Food?

 by Anne Munier

Evolution influences human behaviour by holding on to traits that make us more likely to survive and have babies. Behaviours like avoiding vicious predators, jerking your hand away if you touch something hot, or cooperating with community members all helped our ancestors survive, and have been passed down through generations. Traits that lead to very *unhealthy* outcomes (like, say, having an irresistible urge to play with vicious predators) tend to get weeded out of the population, because kids who play with tigers generally don’t survive long enough to pass on their genes.

So why do so many of us feel compelled to overeat junk food? Junk food, for the sake of this article, means processed foods that are high in sugar, fat, and salt. This type of diet is harmful for our health, yet it is a rare person who craves steamed broccoli over milkshakes, pizza, or brownies.

Oddly enough, these cravings are very much shaped by human, and even pre-human, evolution.

A monkey with a sweet tooth munching on jackfruit

Millions of years ago, some early primates developed a taste for fruit, even though it tends to grow high up in trees, and it’s much easier to munch on plants that are close by. These particular primates did awfully well because fruit has much more energy (i.e. calories) than other foods, and is easier to digest. This leads to healthy primates in good condition to have lots of babies. These babies inherited their parents’ love of fruit, and likewise did better than their counterparts who couldn’t be bothered to climb for their food. And so it continued through the generations, until eventually the whole species were driven to eat as much fruit as possible.

(Fun Fact #1: Primate species that eat the most fruit have the biggest brains.)

Moving along our evolutionary story, early humans were developing ever-larger brains, which, along with our active hunter-forager lifestyles, meant we needed a ton of energy to keep going. We continued to love sugar from fruit or wild honey when we could get it (which wasn’t often), as well as high-fat foods, which are also high in calories. When we had the chance to eat more than we needed, our bodies stored the surplus as fat, allowing people to have more babies, and enhancing survival during times of food scarcity.

(Fun Fact #2: Humans tend to be better at storing fat than other animals. Even super-skinny humans have more body fat than the chunkiest chimpanzee).

Fast forward to the 21^st century -- most of us live in relative prosperity and have constant access to junk food. And while treats that our hunter-gatherer ancestors enjoyed came wrapped up with fiber, vitamins and minerals, today’s treats -- not so much.

We are now hard-wired to seek out sugar and fat, to the point that they stimulate pleasure centres in our brain. This is true for newborns and adults, across all cultures in the world. Healthy food elicits a bit of this pleasure stimulation, junk food elicits A LOT more. And the more junk food we eat, the more we develop a tolerance to it, so we need to eat more to get that same pleasure response. Sound familiar? Addictive substances, including cigarettes and drugs like cocaine, work on our brain in the same way.

Melt-in-your-mouth Cheetos have a very profitable mouth feel.

Then there are the manufacturers of processed junk foods. They want to maximize their profit by selling as much product as they can. And they have all sorts of tricks up their sleeves about how to get us (and keep us!) hooked on the stuff. For example, they figure out a food’s:

• Bliss point: the perfect ratio of sugar, fat, and salt to maximize deliciousness and over-consumption

• Mouth feel: how food interacts with your mouth -- the more quickly it melts, for example, the more it confuses our brain into thinking that we’ve consumed fewer calories than we really have

What is the result of these biological forces on one hand, and the commercial forces on the other?

The number of people who are obese is growing annually, as are associated conditions such as high blood pressure, heart disease, chronic inflammation, and Type 2 diabetes. Add to this the impacts on mental, psychological and dental health, and ballooning health care costs that affect everyone.

So, given enough time, could humans evolve to lose a taste for junk food, since it’s so damaging? Maybe, but let’s not hold our breath. Evolution acts genetically, by passing on genes to our children. But most disease related to excessive junk food affect people later in life, after they’ve already had (or not had) kids.

Is it inevitable then, that we’ll continue to eat excessive amounts of junk food, and our health will keep deteriorating? Not at all! Here are two things to keep in mind as we go forth in our junk food-laden society:

1. Evolution has also endowed us with big beautiful brains capable of critical thought. Even if things are stacked against us, we can make great (if sometimes tough) decisions about our eating and exercise habits.

2. We need to recognize that diet goes beyond will power. Our biology and powerful market forces are designed to make us crave junk food, which, sadly, is often cheaper than whole food. So let’s NOT blame anybody for “lifestyle diseases” caused by too much junk food. Rather let’s consider societal changes that could improve things -- like limiting marketing of junk food to children, or ensuring that healthy food is easily available to all of us. What ideas do you have?

Why Do Kids Play?

by Anne Munier

Kids doing what kids do best!

Children are playful creatures. This holds true all over the world- whether that’s playing 4-square in the schoolyard, engaging in some shadow tag if you happen to be in Ireland, or maybe partaking in a bit of luksong-baka if you’re in the Philippines (it translates to “jump over the cow”, but don’t worry, no real cows are involved!). Even back in the Middle Ages kids made toys out of wood or stones, and long before then, pre-historic toddlers finger-painted on cave walls. No matter where kids are, a day well spent is a day full of fun.

Twig figurines from the American South-West. Toys have been popular for a long time.

And it’s not just human kids -- lots of animals, especially mammals, grow up playing. Think of otters gliding down mud slides on their bellies, puppies wrestling with sticks, baby goats galloping all over each other and head butting anything in sight- they are clearly having fun! The most play-loving of all may be our closest relatives the chimpanzees and bonobos, who laugh, tickle, wrestle, play with dolls (well, with sticks that they treat like dolls, so I’d say that counts), and spend most of their childhood, well, having fun.

All this to say -- playing is genetically ingrained in humans. Kids have evolved to play.

Humans are in good company when it comes to enjoying some good playtime.

But why?? Generally we evolve attributes that help us to survive, be healthy, and have babies. But for most of our evolutionary history we were hunters and gatherers, and playing could have some serious drawbacks. For instance, play:

-Burns lots of energy, so kids need to eat more food (that can be expensive when you’re foraging and hunting every day for survival)

-Is risky -- have you ever known a kid to get hurt or lost when they’re clambering over rocks or climbing trees or exploring new areas?

-Can be loud, which would have attracted the attention of hungry predators.

Having fun? No, these kids are honing their critical thinking skills and coming up with solutions.

None of this sounds like an evolutionarily good idea! But scientists assure us that the benefits of play far outweigh the downsides, by helping kids to:

-Learn skills- children’s games often mimic adult activities, such as playing with toy tools, caring for stuffies, or building sand castles. Play allows for years of practice before taking on real life responsibilities (of renovating buildings, parenting, or designing houses for example). It also gives kids a chance to figure out what they love doing.

-Be strong! All that running around and climbing and wresting and jumping is great exercise.

-Think critically- learn how to analyze situations, come up with solutions, and then evaluate. Think of playing Capture the Flag: your team decides who does what, and how to react to certain situations (like the other team getting too close to your flag). Then you try it out, and chat about how it all went down afterwards. Critical thinking at its finest!

-Communicate, form friendships, develop confidence, and generally get along with others. Social animals (like humans, apes, or wolves) tend to spend more time playing than other species.

-Come up with solutions to life’s problems while having fun! Which, it turns out, is a far better way to learn than when you’re stressed out and running from a charging predator, say. One study observed a group of chimpanzees who all wanted some bananas that were out of reach. Which one figured out how to manoeuver them down with sticks? The one who had had the opportunity to play with sticks beforehand, learning how to manipulate them!

Science backs all this up. Bear cubs that play the most are the most likely to survive the winter. Playful yellow bellied marmots are most likely to have high status as adults. Girls in Botswana who play at pounding grain when they’re young become better grain-pounders (a very challenging job) when older. And children who play more as kids tend to become adults who are good at making friends and adapting to life’s changes.

Keep playing little bear!

The bigger problem today is that kids seem to have *less* playtime than ever before. There may be lots more organized activities in kids’ lives (sports teams, music lessons, tutoring sessions, what have you), but having time to play whatever they want - not so much. Scientists are learning that this is not good for the physical and mental health of children *or* the adults they become.

So, the next time anyone tells you that you’re wasting time playing around rather than doing something serious with your time, you can let them know that millions of years of evolution aren’t wrong. That play *is* serious business, and one of the most important things you can spend your precious time on!

Gene Therapy: Embryonic Engineering and the Future of Human Evolution

by L. E. Carmichael

Welcome to Part 3 of my series on gene therapy and genetic engineering. If you haven't already, I'd suggest reading Parts 1 and 2 before you continue:

Introduction to Gene Therapy: It Sounds Simple, But It's Sure Not Easy

Gene Therapy: Vectors, Viruses, and Why CRISPR Will Change Everything

Today, we're talking about the second major challenge with gene therapy - getting replacement DNA into EVERY affected cell in a patient's body - and why that problem leads to the central ethical debate in this field.

Who Are the Patients?

Gene therapy is designed for patients with genetic diseases. The word "patient" implies a couple of things. First of all, a child or adult that has multiple cells... hence the crux of the gene delivery problem we discussed earlier.

The second critical implication is that patients are autonomous human beings who are capable of understanding the treatment, including its risks and benefits, and are also capable giving their informed consent. Many genetic diseases strike during childhood, and in those cases, parents or guardians are legally permitted to give consent for their children's care.

Carry that thought to its logical extension, and it implies that parents could also have the right to consent to gene therapy on behalf of unborn babies - and specifically, single-celled embryos.

Embryonic Gene Therapy

In September, Chinese scientists announced that they had used CRISPR technology to edit a disease gene in human embryos. If those embryos had been implanted and allowed to develop, they would have been born as disease-free humans. It was an incredible breakthrough... and it opens up a lot of questions.

From a technological standpoint, embryonic gene therapy is absolutely the way to go:

1. If you're doing gene therapy on a fertilized egg - by definition a single cell - the whole problem of delivering functional genes to every affected cell just goes away. Because "every" is now "one."
2. Every cell in the eventual human body descends from that fertilized egg. So every cell in the human being that egg becomes carries the therapy gene. The cure is permanent.
3. That human being's own eggs or sperm will also carry the functional gene. In other words, the cure is not just permanent, but heritable. It will be passed down to the person's own children, meaning one treatment could wipe out the disease from an entire future family tree.

Now We Know We Can... Does That Mean We Should?

The heritability of embryonic gene therapy is the reason that the vast majority of scientists have long considered such procedures unethical - or at the very least, warranting serious discussion. It is one thing to permanently alter the health of an existing human being - we've been doing that for centuries, using medical treatments as diverse as vaccines and surgeries. And indeed, if we have the power to improve someone's life and relieve their suffering, don't we have a moral obligation to at least try?

Altering the genomes of theoretical future humans is another thing entirely. First, because it's much harder to predict the consequences of actions on that scale, and second, because theoretical humans cannot consent to the alteration of their DNA when they do not yet exist. What right do we have to take those choices away? And while it's hard to imagine why someone would want to live with a disease when they didn't have to, our potential to impact the human genome, and therefore the course of human evolution, doesn't stop there.

After all, DNA is DNA. And CRISPR works on ALL the genes, not just the ones that can cause disease.

Embryonic Engineering and "Designer Babies"

Thanks to the Human Genome Project, we have a better understanding of our DNA than ever before. We're finding genes linked to all kinds of interesting traits, like eye colour and height and muscle development and intelligence...

Chinese scientists have genetically engineering dogs with over-developed musculature. Want your kid to be an Olympic power lifter, a soldier, a firefighter? Why bother building the necessary physique with diet and exercise when you could hard-wire their DNA? Ditto if you want your kid to get into Harvard or win a Nobel Prize.There have already been stories about parents undergoing IVF treatments who choose traits like the sex of their unborn child. With genetic engineering, the possibilities are truly becoming limitless.

The Ethics of Gene Therapy and Genomic Engineering

Just because a technology is potentially limitless, doesn't mean it has to be used to its full potential. We have an obligation to decide what uses of gene editing techniques are acceptable and what uses are not, and a further obligation to enforce whatever standards we agree upon.

The ethics of genetic engineering have been debated since the 1970s, when it became possible to manipulate DNA directly for the first time (before that, we had to do it the old fashioned way, using selective breeding). The debates will continue, and in light of these recent Chinese studies, likely intensify. And that's as it should be. Like so many technologies before them, gene therapy and genetic engineering have enormous potential for good, and enormous potential to be abused.

The choice will be up to us.

I hope you've enjoyed learning more about these topics, and I hope you'll continue following news reports about CRISPR and genetic engineering in the news. In the meantime, I'd love to know your thoughts on these issues. Please share and comment!