Why We Are Carrier Mammals

Adriana explains why the type of mammal humans are impacts how much and what kind of care your baby needs from you.

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Why We Are Carrier Mammals

Adriana Lozada:

I’m Adriana Lozada and you’re listening to Birthful. And today just like we do every other week, we’re going to take a deep dive into a fascinating perinatal topic. Today we’re really going to nerd out in the physiology because I wanted to talk about how the type of mammal that we are as humans determines what our babies need from us. And you might say type of mammals, yes type of mammals. Because it turns out that mammals can be classified on a spectrum from altricial to precocial, with the altricial being those that are born very immature that they can’t move that much. They need protection and they need warmth. They can’t regulate their temperature that great, but that protection can be from the environment, like say a den or a burrow, not necessarily having contact with another mammalian body.

Now the precocials they’re well-developed and able to move about at birth. And they tend to stay in very close contact with their mother’s throughout. Now, where do humans fit in, in all of this? That’s the question that Dr Nils Bergman, a Swedish specialist in perinatal neuroscience and also one of the founders of the Kangaroo Care Movement, that’s one of the questions he set out to answer. Dr. Bergman took a closer look at mammalian feeding patterns, their milk composition and how far infants can be away from their parents and for how long they can be away.

And he came up with four general categories of mammals within that altricial to precocial spectrum. These categories are nest mammals, cache mammals, spelled C-A-C-H-E like when a webpage is cached in your browser, follow mammals and carry mammals. All right. So first let’s take a look at the cache mammals, which are very altricial. These are babies that are kind of tucked away in a safe place and parents return to feed them every 12 hours or more. Their milk is very high in protein and fat and that’s to help keep them very full for a long time. Also, because if they get hungry and start crying, crying would alert predators.

So that milk is high in protein, high in fat to keep them full, keep them from crying. And they’re also relatively, quite mature at birth. They can control their own temperatures, they can keep quiet. Some examples of cache mammals are deers and rabbits and also bats. So then if we look at nest mammals, those are less mature at birth than cache mammals or follow mammals. They tend to be born in litters and that is because they need the warmth of the nest or the warmth of others. So they’re not that great at regulating their own temperatures. Their milk is lower in protein and fat than the cache mammals, so they need to eat more often. They usually feed around every two to four hours and so parents returned to the nest several times per day to feed them. Some examples of nest mammals are wolves, dogs, and cats.

Now towards the precocial end of the spectrum, we have follow mammals. And these are baby mammals that are born mature and can walk enough to follow their parents right after birth. They tend to stay close and feed very frequently during the day and night. And they need to do that because their milk content is lower in fat and protein than both the cache or the nest animals. They also have hair to help them control their temperature, which they can do quite well. Again, they’re very mature. Some examples of these follow mammals are cows and giraffes and horses and sheeps and elephants and zebras. You have seen them be born and then immediately start walking, it’s really impressive. So then let’s take a look at carry mammals. And carry mammals are the most immature at birth. They’re completely dependent for food, for warmth, for safety and they also need to be carried constantly because they know they need to be close to a body for all these things.

So they do not like to be put down that feels to them unsafe and it makes them distressed. So then they cry when being separated or feeling unsafe. They are not great at regulating their own temperature, so they need the warmth of other bodies to keep them warm. And if we look at their milk composition, it’s low in fat, low in protein, which means they need to feed around the clock and it tends to be in clustered, frequent and short intervals because their stomachs are not that big. Some examples of carry mammals are apes and marsupials like kangaroos. And so I mentioned that the milk composition of carry mammals is the lowest in protein and fat. And what Dr Nils noticed is that that is also the case of human milk.

Also, our human babies tend to be born very immature, completely dependent for food, for warmth and safety. So ding, ding, ding, if you were thinking humans are carrying mammals, yes we are. If you take a look at the composition of human milk, it is 4% fat, 1% protein, 7% carbohydrate and 88% water. And when I learned that human milk is 88% water, that definitely made sense to me because I remember breastfeeding my baby and being so thirsty. And that is the experience of a lot of people. So make sure when you’re breastfeeding that you have a big glass of water or a container with water next to you. So from this research, Dr. Bergman concluded that human babies are programmed to feed often and to be carried a lot. And this idea that they need to eat every two to three hours with an average of eight to 12 times a day, might actually be too infrequent.

Dr. Bergman talks about having them eat every hour since newborns can only handle about 20ml of milk at a time because of the size of their stomachs and their sleep cycles are just under an hour. So then if you go to eating every hour or so, it would be like feed, sleep, feed, sleep, feed, sleep, and do as much skin to skin as possible. That all brings regulation, it brings calm and is what their biology expects after 2 million years as hunter gatherers and only 10,000 as agriculturists and a bit over a hundred in this more industrialized environments that we’ve got going on today. Because carry mammals tend to be the most immature, they need the protective buffering of an adult body that holds them and feeds them and brings them surges of oxytocin to help grow their brains in a circuitry of connection instead of isolation, which is biologically stressful for them.

So in a way being connected to that body is what helps them complete their path towards maturity, because it’s much more about brain wiring for both baby and the primary parent than just feeding or just holding. So to review four types of mammals, cache, nest, follow, and carry mammals with humans falling into the carry category because the milk composition is low in fat and low in protein, which means our babies need to eat all the time and they also need to be carried all the time. So hopefully understanding this will serve as some form of consolation if you find that your baby won’t let you put them down. And if that is the case, see if you can activate your inner kangaroo and prepare to wear your baby often and feed them often. If you’re wondering for how long this constant contact needs to happen, there isn’t really a hard stop when babies are like, “Nope, I don’t need any more of this type of contact, I don’t need to be carried all the time.”

But there does tend to be a change around three months where babies finally understand that they’re individuals and not connected to you, that they’re actually separate from you. That happens around three months. And then when they start getting more mobile and crawling and their environment expands beyond the safety of your body, then you’ll see that they start spending a lot more time away from you. Because our bodies don’t have pouters like kangaroos do remember that baby carriers are definitely your friends. And so are helpful helpers of the family and friend variety that can hold your baby while you take a shower, have a nap, or take a break. While it is true that your baby needs constant connection that doesn’t mean that it has to be solely from you, remember your village and lean on them as well.

You can connect with Birthful on Instagram at birthfulpodcast. And to learn more about Birthful and my birth and postpartum preparation classes, go to birthful.com. Birthful was created by me, Adriana Lozada, and this episode was produced by LWC Studios: Paulina Velasco, Jen Chien and Kojin Tashiro. Thank you for listening to and sharing Birthful. Be sure to follow us on Apple Podcast, Goodpods, Amazon Music, Spotify, and everywhere you listen, and come back for more ways to inform your intuition.



Lozada, Adriana, host. “What Type of Mammal Are You?” Birthful, Birthful, January 12, 2022. Birthful.com

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