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Carrying Kids: The Incredible Science and Benefits, Part I

Carrying Kids: The Incredible Science and Benefits, Part I

Carrying children is one of the original forms of rucking. It changed our species and still benefits us and kids today.

Why it matters: Carrying children played a vital role in human evolution, development, and fitness. Even if you don’t have a kid, you can learn something from it.

Quick housekeeping + what’s coming this week:

  • Members keep 2% alive. I’m encouraging everyone to become a Member. Sign up here.

  • Wednesday we’ll follow up on this post with a handful of ideas and tips on four topics related to carrying kids and how you can apply the lessons from the evolution of child carrying to your daily life to improve your health and fitness (even if you don’t have kids).

  • Friday we’re launching a new series called The Expedition. It’s a delve into what I’ve been reading, listening to, thinking about, and more.

  • This post will be useful to anyone who has a baby or toddler in their life (parents, grandparents, family, friends). Please consider sharing it.

Now let’s get into it. Thanks to popularity of The Comfort Crisis, I get a lot of questions about rucking.

One of the most common is: Does carrying my child count as rucking?

The answer is a resounding yes. Carrying a child is actually more challenging than carrying an equivalent amount of dead weight.

When the weight you carry is in the form of a kid, it squirms around, screams in your ear, and may even vomit down your neck.

And it turns out that carrying kids is important. Really important.

It changes the carrier and carried and shaped humans into who we are today. This post will cover:

  • Why we evolved to carry our kids more than other animals, and how this changed us.
  • Why carrying kids helps them learn language better.
  • Why carrying kids improves their physical abilities.
  • Why kids who are carried more do better emotionally.
  • Why carrying makes kids and parents happier.
  • Why carrying kids improves the physical health and fitness of parents.

Let’s roll …

Carrying kids—an evolutionary heritage

In 2020, a group of anthropologists and biologists from five different universities across the world looked at all the research on carrying kids.

If you read The Comfort Crisis, you know that humans are born to carry. We’re the only animal that can carry items long distances on our own. Carrying shaped us. It allowed us to become apex predators and take over the world.

  • We’d carry hunted meat and gathered food back to camp.
  • We’d carry tools into the unknown so we could explore more of the globe.
  • We’d carry weapons into battle.
  • And we would, of course, carry our children.

Humans carry our offspring more and longer than most other animals.

Here’s why: Human children take a long time to mature—we spend twice as long in childhood and adolescence compared to our closest animal relatives like chimps and other primates.

We can thank our big brains and narrow pelvises for our slow development.

Our narrow pelvises are a killer adaptation that allow us to walk upright and cover long distances. But these narrower pelvises also changed how we can develop in the womb.

Here’s how our bodies compare to three of our ancestors who lived 2 to 4 million years ago. All the pelvises are relatively narrow.

If a baby’s brain was fully formed in the womb, it would be impossible for the baby to exit. A mother’s pelvis just isn’t wide enough.

Evolution’s solution was simple. Whereas most other mammals’ brains develop more in the womb, human brains develop mostly outside of the womb. We basically get shot out into the world with a brain that is entirely useless.

We take years to be able to do anything on our own. But the tradeoff is that we eventually walk upright and have the most brilliant brain in the animal kingdom.

In fact, a human brain isn’t fully developed until about age 25. (This, mom and everyone else in Davis County, Utah, explains my idiotic behavior in high school.)

How this relates to carrying

Because our brain is doing so much catching up when we’re an infant, it takes us a long time to become mobile on our own. Many other animals start walking immediately upon exiting the womb. Like giraffes, horses, pigs, and camels.

Meanwhile, it takes most human babies about 12 to 15 months to learn to walk. That’s about 2.5 times longer than our closest animal relatives.

And once human babies can walk, they take a long time to get good at it. They’re clumsy. Their endurance sucks. So they still require occasional carrying for years after that.

Which brings us back to that international team of scientists. Because our parents have to carry us for so long when we’re babies and toddlers, the scientists wanted to know the role carrying kids played in human evolution and how it changed us.

  • Those scientists wrote, “In an evolutionary aspect, human infants have been carried for at least 6 million years. If we consider our non-human ancestors as well, offspring are genetically predisposed to being carried for 55 million years, since Primates started to emerge.”
  • They continued, “We humans are born with an evolutionary preadaptation: The ability to cling and to be able to carry our infants. Nurturing in accordance with a 55-million-year-old evolutionary heritage is more likely to result in mentally and physically healthy and resilient individuals in this and future generations.”

They uncovered fascinating facts about carrying children that still apply to kids today. It makes a strong case not only for carrying children, but mimicking how children are carried if you don’t have any.

Kids learn language better when carried

In short

Carried kids learn more faster.

The details

When early humans started carrying their kids, it “opened up new ways of learning by observing visual and auditory stimuli simultaneously,” the scientists wrote.

Think about it. When you carry a child, it’s in the middle of whatever you’re doing, seeing and hearing the world as you do. The position, “provide(s) a safe place and vantage point for learning in the most critical first year of life.”

Perhaps most important is that the child is thrust into the middle of your interactions with other humans. In turn, she can watch other people’s faces and mannerism, and eventually mirror their behaviors. It’s how we being to learn how to be a human with other humans.

These two kids in Mozambique are in the middle of their moms’ social interactions. Also: Props to the woman in the background for sending out the best stink eye ever.

The scientists wrote that once we started carrying children, “language development boosted, which facilitated communication, (and) therefore advanced social bonds.”

Kids gain important physical skills when carried

In short

Infants test four important physical skills when they’re carried. These help their body, brain, and central nervous system develop appropriately.

The details

When you put an infant in a crib or car seat or lie it on the floor, it just sort of lays there. It’s so weak it can hardly do anything but move its arms and legs a bit.

But when you carry the child, some important physical skills are tested and developed.

Head and neck control

The infant has to work their neck to keep their head upright. The researchers say this builds their vestibular system. That system is responsible for balance, knowing where your body is in space, and coordinating your movement with balance.

It also begins to strengthen their core and stabilizing muscles.


When you place your finger in a baby’s hand, she’ll grasp it. This is an innate reflex that likely evolved to help babies be carried.

Babies reflexively grasp your skin or clothing when carried. The scientists wrote that this helps them stabilize their torso and triggers other bodily responses. It “keeps the infant a reflexively-active participant while eliciting compensatory responses.” Translation: They’re learning how to move and react to the world.

The “Moro reflex”

The Moro reflex is a response that kicks on when an infant loses balance. They extend their arms and legs, then pull their arms in, and sometimes cry. It’s also been described as the “embracing reflex.” Scientists think that its role is to help and teach and infant to cling to their parent and regain hold. It seems to help the baby’s central nervous system develop.


When a baby’s foot touches a flat surface, it will make walking motions even though it’s months from walking. This is elicited in carrying as well. Scientists think that it helps babies cling and adjust themselves when being carried, and it sets the movement patterns needed to eventually walk.

Kids relax when their parent carries them

In short

Carrying a child elicits a natural reaction that calms both the parent and the baby, and it might be necessary for children to become healthy, stable, resilient adults.

The details

When a baby’s mother picks her up, it’s like they’ve both just popped a sedative. Both of their heart rates drop and sync up. Scientists call this the “transport response.”

The baby relaxes. It’s stress markers drop and it’s likely to stop crying. Even when an infant isn’t crying, being picked up and carried by mom drops their heart rate (suggesting reduced stress).

  • Why this happens: The scientists think the “transport response” improved survival. Let’s say there’s a predator nearby. If you pick up the baby and hug it tight and the baby stops crying or is less likely to cry, you’ll be less likely to be detected.
  • One fascinating fact: Heart rate doesn’t drop as much if a stranger picks up the baby.
  • Most important: The scientists wrote that babies who are frequently carried “appear more likely to thrive, becoming healthy and stable adults, even if their life is stressful. If infants do not receive the necessary body contact … the lack of it may cause long-term negative effects on their physical and mental health.”

Kids and parents become happier from carrying

In short

Parents who don’t have as much skin-to-skin contact with their children are more likely to be depressed.

The details

Carrying not only seems to improve the happiness of babies, it also makes parents happier.

For example, one study discovered that mothers who didn’t have skin-to-skin contact with their kids experienced more symptoms of depression than did a group who carried their children every day.

This holds for fathers too.

Parents work their bodies when carrying kids

In short

Carrying a 7 to 25 pound weight around is physical work that keeps us healthy and build strength in the areas we need it most.

The details

Babies need to be carried all the time until they hit about two years old and turn into infants. Still then, you’ll occasionally carry them.

Babies weigh an average of seven to eight pounds. They gain a pound or two a month until they reach two. The average two year old weighs about 25 pounds.

All that weight carrying makes every movement more challenging. Like, you’re basically living life while carrying a dumbbell in your arms, at your side, slung across your front or back.

This woman wins the carrying Olympics.

Moving with weight leads us to preferentially burn fat over muscle (cardio alone burns a higher ratio of muscle to fat).

And because we carry kids in all different positions—hugged, in our right arm or left arm, at our right hip or left hip—and squirming around, it stimulates and strengthens all sorts of muscle groups. Especially our core.

And good core strength is one of the best ways to prevent and relieve back pain. About 80 percent of Americans will experience back pain, and most of this pain is “non-specific.” It emerges because the core muscles that protect our spine have become weak due to our newfound sedentary lifestyles.

Bonus fun fact: Right handedness may have evolved from carrying kids

In short

Most people are right handed possibly thanks to how women prefer to carry children.

The details

Anywhere from 70 to 85 percent of women hold infants on their left. This applies to women who are left handed, and we even see it in young girls carrying dolls. Babies also seem to prefer to be carried on the left side.

In 1983, the famed neuroscientist and evolutionary biologist William Calvin theorized that our tendency for “right-handedness is derived from infants carried by the left arm because it is the infant’s preference, hence leaving the parents’ right arm and hand free for manipulation.”

Wednesday will be Part II of this post. We’ll cover:

  • How rucking evolved from carrying kids (this is crazy fascinating).
  • How to carry kids in the safest and most beneficial way.
  • How to apply the lessons from the evolution of child carrying to your daily life to improve your health and fitness (even if you don’t have kids).
  • How to apply these lessons to relieve common physical pains like back pain.

Thanks for reading.

Have fun, don’t die, carry your kids.


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