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The University of Texas at Austin. Illustration by Jenna Luecke.

Our Gut Microbiome Evolved Alongside Us, Study Finds

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The University of Texas at Austin. Illustration by Jenna Luecke.

A new study in the journal Science examining the genetics of the bacteria living in the guts of African great apes and people from Connecticut supports the idea that our microbiome has been evolving with us, despite bacteria-affecting changes in environment, diet, geography, and for humans, medicine usage.

Using fecal samples, an international team of scientists led by researchers from the University of Texas at Austin created evolutionary trees for three different groups of bacteria that make up one-fifth of the human gut microbiome, tracing bacterial species back millions of years. They found that our gut microbiome can be traced all the way back to before the human species existed, to the common ancestor that both humans and great apes evolved from millions of years ago. Gut microbes have evolved in parallel with the different species, they say, with genetic splits in bacteria occurring at the same time as gorillas diverged from other hominids about 15.6 million years ago (which is much earlier than some previous estimates) and humans split from chimps and bonobos roughly 5.3 million years ago.

This means that though our environment does affect our microbiome (eating less fiber, for instance, has been shown to alter the bacterial makeup, as has using deodorant), genetics play a major role in the types of species we play host to.

There’s potential that some of our bacterial lineage may be shared with species even farther back in the evolutionary tree, the researchers say. “Maybe we can trace our gut microbes back to our common ancestors with all mammals, all reptiles, all amphibians, maybe even all vertebrates,” study author Andrew Moeller postulates. This research doesn’t dive quite so deep, but future studies might explore those issues.

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Animals
Why Do Female Spotted Hyenas Give Birth Through Their Pseudo-Penises?
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YouTube

At the zoo, you can sometimes tell the difference between male and female animals by noting their physical size, their behavior, and yes, their nether regions. Hyenas, however, flip the script: Not only are lady spotted hyenas bigger and meaner than their male counterparts, ruling the pack with an iron paw, they also sport what appear to be penises—shaft, scrotum, and all.

"Appear" is the key word here: These 7-inch-long phalluses don't produce sperm, so they're technically really long clitorises in disguise. But why do female hyenas have them? And do they actually have to (gulp) give birth through them? Wouldn't that hurt … a lot?

The short answers to these questions are, respectively, "We don't know," "Yes," and "OW." Longer answers can be found in this MinuteEarth video, which provides the full lowdown on hyena sex. Don't say we didn't warn you.

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Animals
The Science Behind the Urge to Cuddle Cute Babies
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You don’t have to be a cat person to feel your heart warm up at the sight of a big-eyed, tiny-nosed kitten stumbling across the floor. When confronted with a baby kitty, you may feel the urge to scoop it up and cuddle with it for the rest of the day. This reaction isn’t limited to felines—puppies and even some adult animals trigger these same snuggle instincts. If this feeling sounds familiar, that means your brain is just doing what it evolved to do to preserve the human species.

This episode of the National Geographic video series We’re Wired That Way lays out what's going on in your head when you see something cute. The facial features of most young mammals fall into the same configuration: large round eyes, and small noses, mouths, and chins. This is called kinderschema, and humans are engineered to find it adorable because it can be found in our own babies. When we see a typical baby face, it activates our instincts to nurture and protect while also releasing the feel-good chemical dopamine to reward us for doing so. That way we feel driven to keep babies safe even if they’re not our own, thus boosting their chances of survival and the survival of our species.

Because kinderschema isn’t limited to the human race, we feel this response when looking at non-human baby animals as well. Some mammals, like cats and guinea pigs, retain their kinderschema into adulthood. So next time you let out an involuntary squee at the sight of your pet, remember that you have biology to blame.

[h/t National Geographic]

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