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How do you decide whether a stranger is a good person or not? Your first response might be that you don’t judge people until you get to know them better.

But even though that’s probably a good thing to aspire to most of the time, it’s not how we evolved. Humans are social animals, and it’s important for us to be able to quickly form judgments about whether a stranger is trustworthy or someone we should avoid. On the other hand, we tend to be flexible in those judgments.

And in a study published this week in the journal Nature Human Behavior, researchers found that we seem to be predisposed towards forgiveness. Across several experiments, the team had more than 1,000 people watch actors decide whether or not to give someone an electric shock in exchange for money. As participants observed the actor’s behavior, they were asked to predict what the stranger would do next based on what they’d seen them do so far.

They also rated how confident they were about the predictions. Unsurprisingly, the subjects quickly formed positive impressions of good strangers -- the ones who chose not to give the electric shocks -- and were confident in their predictions that those people would continue to be kind. When it came to the bad strangers, though, participants had a different reaction.

Even when they saw someone choose to deliver a painful electric shock in return for cash, they didn’t feel as confident that the person they were watching was really a bad person. And they were willing to change their minds quickly when presented with new evidence -- as soon as they saw a supposedly bad stranger show mercy, their opinion of the stranger improved … at least until the next offense. This tendency to give strangers the benefit of the doubt might not extend to more extreme situations, like if the person on the receiving end of the shock was a loved one.

But there seems to be something unique about how we form judgments of people’s character. Previous studies where participants judged a stranger’s skill at a task, rather than their morals, didn’t find any similar flexibility in the predictions about lower-skilled versus higher-skilled people. So apparently all that old advice like, “never hold a grudge,” “don’t let the sun set on your anger,” and “forgive and forget” is actually backed up by our social evolution.

Because yeah, it’s important to know if someone isn’t trustworthy. But if you write them off as a bad apple too quickly, you might miss out on the benefits of a potential relationship with them. So we may be quick to judge … but at least we’re also quick to forgive.

It’s all in the inner workings of our minds. Meanwhile, other research published this week looked at the inner workings of our bones. In a study published Thursday in the journal Cell, scientists found a whole new type of stem cell — those blank slates that can give rise to all the different types of cells we need to function.

Biologists have found a bunch of different types of stem cells so far, like in the brain and bone marrow. Now, for the first time, they’ve isolated the stem cells in our skeletons that produce bone tissue and cartilage — a discovery that could someday help us treat injuries and diseases that affect the skeletal system. The different kinds of stem cells are classified according their potential to differentiate into various cell types.

And although skeletal stem cells had been observed in lab mice, no one had managed to find them in humans before. In the past, attempts to isolate stem cells from bone depended on getting bone marrow cells to stick to plastic plates. But this technique often resulted in cultures that contained a mix of cells at different stages of differentiation.

To finally find true skeletal stem cells, the team sequenced the RNA of individual cells from two areas of the femur in a human fetus. RNA is the messenger molecule that tells your cells which parts of your DNA to actually turn into proteins. So by sequencing RNA instead of DNA, the researchers could tell which specific genes an individual cell was expressing, and identify the ones most similar to the skeletal stem cells in mice.

Once they knew what they were looking for, the researchers were able to find skeletal stem cells in adult bone tissue, too, and even generate them from induced pluripotent stem cells. Those are adult blood or skin cells that scientists have reprogrammed back into stem cell blank slates. Finally, the team mapped out the steps involved in forming skeletal tissues -- the different stages between undifferentiated stem cell and finished product.

There’s plenty more to learn about how exactly we make all the different types of cells in our bodies -- besides cartilage and bone, our skeletal systems also include some fatty tissue, and those fat cells don’t come from the stem cells ID’d by this study. We’re not at the point where you can grow a whole new bone in a lab from your own stem cells or anything. But there are lots of diseases that affect bones and cartilage — from the obvious ones like osteoporosis and arthritis, to the more indirect problems that come from things like diabetes.

And finding skeletal stem cells, figuring out how to make them, and knowing how to turn them into bone and cartilage cells opens up all kinds of new possibilities for diagnosing and treating those issues. Thanks for watching this episode of SciShow News! So, here’s an exciting thing: You might have noticed that on our Quiz Show episodes, one of our presenters wears a SciShow lab coat like this one while they talk about the answers to the questions.

Well, now you can get your very own SciShow lab coat over at DFTBA.com/scishow! There’s a limited number of them though, so get ‘em while they’re hot! [OUTRO♩].