If you’ve had a cup of coffee with cream
lately, or maybe cereal with milk, you’ve come to the right place. Because, while you may not have thought of
it then, milk is weird. Well, the liquid itself isn’t that weird.
It’s super useful. But the way that we use it? That’s weird. I mean, milk is for babies. That’s why it
was made. Plenty of adult humans drink it anyway, like
myself, and the milk we drink mostly comes from cows. But there are lots of other options out there
-- including the fattiest and skimmest milks known. You just probably wouldn’t want to drink
them. Milk is produced by modified sweat glands
in mammals called mammary glands, and it’s used to give baby animals the nutrients they
need before they can digest other food. All mammals produce milk--it’s where we
get the name Mammalia, and it’s one of the three defining features of mammals, along
with hair and three middle ear bones. Humans, being mammals, also make and drink
milk. But we’ve done something no other animal
has: We’ve taken this nutrient-rich baby food
and, through genetic mutation, turned it into a digestible, dietary staples for humans of
all ages. But most people don’t continue to drink
human milk throughout their lives. If they did, it would mean a human would have
had to sacrifice the calories necessary to make the milk, which would have totally defeated
the purpose back when we were starting to use it as an extra source of nutrients. So instead, we drink the milk of other animals. People around the world drink milk -- and
make other food products from -- animals like yak, reindeer, water buffalo, elk, and horses. In the US and Europe, dairy consumption is
mostly limited to the mammary secretions of sheep, goats, and cows. But really, mostly cows. Why? Well, first, picture a cow. They’re
big and they’re pretty nice. Over generations of selective breeding, we’ve
created creatures who can give between six and seven gallons of milk a day, and they’re
domesticated enough to just line up to do it. Goats and sheep, while they’ve also been
bred to produce more milk and be more willing to do so, can only produce about a gallon
of milk a day. By economics alone, cows are the better milk
producers. But it’s also a matter of taste. Cow’s milk has a fat content similar to
human milk -- about 3.5% versus a human’s 4.5% -- which makes it familiar, at least
if you want to drink whole milk. By comparison, the water buffalo, which produces
the milk that gives the world buffalo mozzarella, has a fat content of almost 7 percent -- great
for cheese, but maybe not the best for drinking. These animal milks all have different fat
content, because it depends on the animal’s environment and the way that they nurse. If you’re looking for the very fattiest
known milk, you’ll have to find a hooded seal -- their milk is about 60% fat. That’s because hooded seal pups are born
on floating sea ice in the North Atlantic and Arctic oceans. The harsh temperatures and the instability
of the environment mean that the pups have to put on a lot of fat really fast. They only
nurse for about four days, but almost double their weight in that time. By comparison, heavy cream is usually around
36% fat. Even if you wanted to hang out in the freezing,
icy ocean, drinking this stuff would be like trying to drink really fatty peanut butter. At the opposite extreme, the skimmest known
milk comes from the black rhinoceros, with a fat content of around 0.2%. The watery milk probably has to do with their
long nursing period: black rhino moms nurse their young for almost two years, and pouring
a ton of fat into their milk for that long would use up a lot of resources. But if you wanted to try some out, you might
have some trouble tracking it down. For one thing, black rhinos are critically
endangered, so it would be tough to find one in the first place. And even if you did find one…it’s still
a rhinoceros. Have you seen one of those things? About a third of the females and half the
males die from fights with other animals. Unless you’re a baby rhinoceros, a nursing
rhino mom is probably not going to let you walk up and take a swig. Now, before we sign off, I want to clear up
one milky myth that gets repeated a lot. Hippopotamuses are mammals, and they make
milk. You may have heard that it is pink, but it
is not. Hippo milk is whitish, just like all other
milk. This misconception probably comes from the
fact that hippos do secrete a super useful mucus on their skin that helps protect against
UV rays and works as an antibiotic. And the mucus is a reddish color. But it is not milk! Though, again, you probably wouldn’t want
to go up to a hippo and check. Thank you for watching this episode of SciShow,
which was brought to you by our patrons on Patreon. If you want to help us spread more
tasty science, you can go to patreon.com/scishow. And don’t forget to go to youtube.com/scishow
and subscribe!
This was awesome! Milk is totally weird.