(Describer) On a video:

Subject A-34, Neonatal Intelligence Battery, trial 17, hour four. Let's just get on with it. OK, just going to solve for x.

(Describer) With a baby...

(Describer) The baby takes a marker and draws.

Looking for more numbers.

(Describer) The baby hits the table with it.

We'll just-- oh, I'm going to-- we'll get back to that one later. OK, just going to start my watch.

(Describer) The baby gets a Rubik's Cube.

Unorthodox.

[baby chattering]

It is challenging. Yes. We're at 47 minutes.

(Describer) The baby throws it.

Oh, well if that's how you're going to play, then fine.

(Describer) With two blocks...

What is the relationship between the two objects? I think he's going to get this one. And he's eating it.

(Describer) He reaches for a notebook.

You can't cheat. Marks off for that. Okay, this...

(Describer) The baby slides a paper off the table.

Can you spell p--

(Describer) He throws down the cube.

can you spell pitui-- can you spell p? That is incorrect.

(Describer) The baby drools.

Hey, smart people. Joe here. The first thing a baby giraffe experiences after being born is a two-meter fall straight down to the ground. But within an hour, it's standing, walking, and nursing on its own. And a blue whale calf, after nearly a year growing inside Mom, can swim to the surface moments after being born. Human babies on the other hand, we are born unable to move or eat on our own, we can't communicate or fully sense our world, and we leak everywhere. If humans are so smart, why are our babies so unsmart? Human babies begin life so undeveloped that many people refer to a baby's first few months of life as the fourth trimester. Compared to other animals, we lie on the altricial end of the spectrum. Compare that with, say, a baby cow, a precocial animal whose brain and body is developed enough that they can stand and run just moments after being born. Tiny humans require a ton of parental care before we're ready to be on our own. Our parents not only grow us for nine months or so, they carry us, they feed us, they keep us from dying, and they teach us how to provide for ourselves for 15, 18 years. Heck, these days even over 30 isn't unheard of. It's actually totally normal--

MOM: Wah, wah. Wah, wah, wah, wah.

(Describer) He looks up.

JOE: Ma, I'm shooting a video down here. Gah, just start over and edit this. That's because, well, our brains come out half-cooked at best. When we're born, our brain is around 30% the size of our adult brain. That's the smallest of all of our primate relatives. So why does our smart species have such small-brained babies? Well, for a long time, scientists' best answer to that question was the obstetric dilemma. Basically, our brains come out as big as they physically can be. The obstetric dilemma goes like this-- if our brains were any bigger at birth, they wouldn't fit out the birth canal. And if female pelvises were any wider, they would make walking and running less efficient, which might not affect your life that much, but it would have made it easier for our ancestors to become dinner, which means no babies, which means no you or me. So here, natural selection found a compromise. Mom's pelvis stays narrow enough to walk and run, and babies are born earlier so their noggins don't get stuck. It's a pretty logical idea. But it doesn't hold water. Male and female bodies do have significant anatomical differences. But research has found that wider or roomier pelvises don't make walking and running, a.k.a. locomotion...

[fanfare]

less efficient. And some women already have pelvic openings wide enough to fit bigger heads and brains. Not every woman does, but if there was strong pressure from natural selection for roomier pelvises, they'd have become more common. So pelvis size isn't why our babies come out half-baked. The real answer might have more to do with metabolism. The bigger a developing baby gets, the more demands from mom. I mean, women grow a completely new organ, the placenta, not to mention a complete human being inside their bodies. And that takes energy. It might be that Mom's ability to provide enough energy for growing baby determines when baby is born. Humans and all other animals have what's called a basal metabolic rate. It's how much energy we burn when we're not doing anything else. Tour de France cyclists at peak human performance can hit maybe four or five times their base metabolism. But most of us normal humans, we max out at around two times our basal rate. We just can't run our biological engines any higher for very long. It's like overclocking a CPU. There's just a physical limit to how much extra energy we can create. For the last third of a pregnancy, and even into nursing, a mother is at the limit, burning twice as much energy as before baby. Nine months happens to be right about the time a growing baby starts to demand more energy than Mom can provide, so it's born. It's called the EGG hypothesis, or Energetics of Gestation and Fetal Growth. But I like EGG. But even energy and metabolism might not be the full answer. It could be that how helpless our babies are when they're born has had a big influence on what happens after they're born. Now, how self-sufficient an animal's young are at birth can be determined by a lot of things-- if they have to run from predators, if their parents are quickly on the move, or if their egg just had enough nutrients to hatch big. But having helpless babies and helping them get smarter might have forced ancient human parents to get smarter too. It's a pretty cool theory and works like this-- when we look at human ancestors, it's clear that natural selection favored humans with larger brains because they tended to be smarter. But human babies' brains are already born as big as they can be because of the whole energy thing. So the only way to make a bigger brain is for the brain to spend more time growing after you're born. That requires longer parental care, which requires more intelligent parents, which over time selects for parents with bigger brains. It's a feedback loop. The more intelligent the parents, the better and longer they can care for a little helpless baby, and the bigger the baby's brain can eventually grow. Research tells us that modern human brains don't finish developing until about age 25, which means I have been past my peak for a while. But it supports this idea that intelligent parents caring for their children for longer have helped extend the amount of time that our brains get to grow before they're done. More intelligence probably made early human ancestors more social, too, which made raising helpless young even easier, which would start a whole other feedback loop, making us more and more social over time. And these aren't the kinds of things that you'd notice in a generation or two. They'd evolve across hundreds of generations. There are definitely other reasons that our ancestors' brains grew. Making tools and hunting animals, that helped a lot. Harnessing fire and cooking food to get more calories and nutrients helped too. But ask any parent, it is not easy to raise a helpless baby, especially for a decade or two like humans do. It takes our unique intelligence and our unique social abilities to do it. I mean, you give a human baby to a group of chimpanzees, it's not going to end well. In the end, like all interesting and complex human traits, our extreme intelligence and our babies' relative lack thereof can't be explained by just one reason. It's a mix of many reasons. Having a baby is not an easy thing to do. But the very fact that humans are so good at having more humans and caring for them and each other as deeply and for as long as we do is proof enough that we're a very special species indeed. Stay curious.