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Centuries before bathtubs were invented, unwashed cave dwellers had no idea their body odor was offensive.

According to research published in Nature, your nose can detect about one trillion smells. But one smell it can't detect is your own body odor.

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Religious theologians say humans can't detect our body odor to prevent us from becoming depressed. Also, our offensive body odor was necessary to ward off predators.
 
RELATED: 8 foods that actually make you smell bad
 
God, in His infinite wisdom, blocked our ability to detect our own body odor.

However, the game changed forever when man invented soap and razors. That's when the population exploded.

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Pamela Dalton, a psychologist at the Monell Chemical Senses Center in Philadelphia, explained to the Washington Post that the brain also blocks our body odor to make room for more important smells -- like pizza or danger.

"If your sense of smell was bogged down by your body odor -- or other standard smells -- we might not be able to detect the more important odors."

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Is your mom kinder to her grandchild than she was with you? A new study says you're not imagining things.

Retired pop singer Beyonce (left) recalls the day her mom, Tina Lawson slapped the taste out of her mouth for ignoring her in a store.

"I was about 15 and the song was playing on the radio and I'm like 'Yeah!' and these guys were looking like 'Ooooh that's Beyoncé' and I thought I was hot. And she smacked the crap outta me in that store."

Tina said, "I don't care what song you have on the radio - you are my child. You do not disrespect me."

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Tina is considerably kinder to her granddaughter, Blue Ivy, than she was with Beyonce.

According to a new study, biology is the main reason your mom is kinder and more patient with her grandchild than she was with you.

The research was conducted by author James Rilling, a professor of anthropology and professor of psychiatry and behavioral sciences at Emory University in Atlanta.

Rilling discovered grandmothers showed significant neurological changes when they underwent brain scans with functional magnetic resonance imaging (fMRI).

50 grandmothers participated in the study. They were shown pictures of their grandkids, their adult children, and a stranger.

When shown photos of their grandchildren, grandmothers had measurable brain activity and changes in blood flow when shown photos of their grandkids.

The pupils in their eyes also changed size when they saw a photo of their grandchild.

Their brain scans showed more cognitive empathy when looking at photos of their own child.

However, when looking at a grandchild, they showed stronger emotional empathy than they did with their own children.