No two mothers are alike (except for the fact that they all love candles). But through the lens of science, some spectacular similarities do shine through. Evolution has shaped generations of mothers and their relationships with their kids. As scientists have shown, the genetic inheritance we receive from our moms goes far beyond the X chromosomes they pass down, seeping into our brains and our behavior.

The relationship goes both ways. Children also have measurable effects on their mothers, meaning that the next time your mom asks when you’re coming home, you can technically say that you’re always with her (but you should probably visit too). Below are some of the ways we’re attached to our biological mothers and how they’re attached to us. Of course, there are many beautiful ways to be a mother outside of having a biological relationship; unfortunately, there aren’t enough studies yet on the families that you get to choose.

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There's a biological attachment between mothers and their kids.

Mom’s Voice Lights Up Our Brains

When you go to a grocery with your mom, somehow you can always hear her yelling for you to grab some dip from across the store. There’s no explanation for that yet, but scientists do know that children uniquely respond to the sound of their mother’s voice. In 2016, researchers from the Stanford University School of Medicine showed that children’s brains are more engaged when their hear their mother’s voice and that the sound of her voice activates very specific parts of their brains.

The team showed this through an experiment in which 24 kids aged seven to 12 had their brains scanned while they listened to recordings of either their mother or random women say nonsense words (the idea being that meaningless words wouldn’t trigger other parts of the brain). When an individual mom said those words, the parts of her kids’ brains related to emotion and reward processing, social functioning, relevance detection, and face recognition became activated. While it had been established that hearing a mother’s voice brought her children emotional comfort, this was the first time that “biological circuitry” could be linked to the experience. Moms have “quick access to so many different brain systems,” the team writes, which is really a mom’s dream come true.

A Special Chemical Puts the Female Brain in Mom Mode

Looking at a baby may give you far less pleasure than looking at a puppy now, but that likely will change if you ever have your own child. In a 2014 study on mice published in Nature, a team of researchers showed that the “love hormone” oxytocin flips the brain into a maternal state.

The study is based on the fact that, on both sides of the mouse auditory cortex, there are oxytocin receptors and oxytocin-producing neurons. The team hypothesized that these receptors and their proximity to the hearing system could explain why mice — and human mothers — quickly respond to the sounds of their children. Injecting oxytocin into the left auditory cortex of female mice who’d never had children immediately caused them to respond to the calls of baby mice. The surge of oxytocin seemed to transform their behavior and their interpretation to social cues, which the scientists think also applies to happens to new human mothers, whose brains also get flooded with the chemical.

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The sound of a mother's voice and heart affects a child's brain development.

We Inherit Some of our Mother’s Fears

In another rodent study, scientists showed that maternal fear responses could be passed down to their children just by limited exposure to the fear stimuli. The 2014 paper, published in PNAS, showed that scents alone can pass fear onto newborns. In the experiment, female rats were first conditioned using electric shocks to fear the smell of peppermint. Then, the rats were impregnated. When the pups were born, they too were exposed to the peppermint smell but were not given a shock. Nevertheless, the pups were still afraid when exposed to peppermint, even when their mother wasn’t present. This may explain why, in humans, PTSD and certain phobias can sometimes be passed down from mothers to children.

Brains Get a Boost From a Mom’s Heartbeat

A 2015 study from researchers at Brigham and Women’s Hospital in Boston found that our brains are not only activated by the sound of our mother’s voices but also actually grow because of it. Twenty premature babies, who had spent more time in an incubator than with their moms, were studied as the sound of their mother’s voice and heartbeat were pumped into the incubators with tiny speakers. The babies, each born between eight to 15 weeks early, listened to these recordings three times a day for 30 days, while a control group of another 20 didn’t get the private DJ session.

By the end of the experiment, the scientists concluded that the experimental group had developed significantly larger auditory cortexes than the control group. In other words, the sounds from their mothers actually made parts of their brains grow. If only calling your mom during finals could give you that same brain-growing boost as well.

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A fetuses' cells are passed through to the mom via the placenta.

Our Cells Are in our Moms — and Vice Versa

We may inherit genes from our mothers, but while we’re in the womb, we pass on some of our genetic material to them as well through the form of cells. As a mother’s placenta grows, it attaches to her arteries, creating a two-way channel between her and her baby. Large amounts of fetal material are slurped off into her bloodstream, leaving mom with her infant’s cells entering her organs, becoming heart muscle cells, and sometimes even turning into neurons. A 2015 study in Molecular Human Reproduction found that tissue samples of women who had died during or just after pregnancy and were pregnant with boys had male cells in their brains, hearts, and kidneys — with roughly one cell out of every 1,000 being male.

For a time, scientists thought that these fetal cells in mothers may pose a danger, perhaps increasing the likelihood of developing autoimmune disorders. But more recently, scientists have shown that these cells actually help moms be healthy and decrease the likelihood of developing cancer and cardiovascular disease. On the flip side, cells from moms cross the placenta and enter the fetal body — meaning that you have a bit of her cells as well.