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updated 12/29/2008 1:47:46 PM ET 2008-12-29T18:47:46

Visiting — or even just viewing photos of family members — prompts brain activity that affects how you feel about them, your friends, and even yourself, a new study suggests.

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The study is the first to compare brain activity associated with seeing relatives with that linked to seeing friends and strangers. It suggests our feelings about biological relatives are at least somewhat primal.

The findings may help explain everything from why our family can get on our nerves to why people who look like us can spark immediate feelings of trust, "but not lust," said Steven Platek, who co-authored the study with Shelly Kemp.

"We like to be around people that look more like us, but we do not find them as sexually attractive," added Platek, editor-in-chief of the journal Frontiers in Evolutionary Neuroscience. "I think it is linked to our subconscious ability to detect facial resemblances so we avoid lusting after those that may be related to us."

For the study, the researchers performed MRI brain scans on test subjects viewing images of biological relatives, friends, strangers, themselves and various morphed images. Video: Is holiday stress making you fat?

The scientists found that relatives and self-lookalikes are processed through a self-referential part of the brain. Friends and strangers who look nothing like the viewer, on the other hand, light up entirely different areas of the brain, those linked to making important and risky decisions with respect to the self.

The findings are published in the latest issue of the journal Neuropsychologia.

Platek and Kemp also found that the brain ranks everyone socially, with relatives at the head of the line.

"I think facial resemblance is ranked right up there in importance with attractiveness," Platek said.

Since relatives are processed through areas of the brain linked to self-reference, the study could also help to explain why relatives cause us to take things personally. While we may tolerate a friend's loud laughter or snoring, for example, we may have less patience with a relative because we judge them similarly to how we judge ourselves.

"This research is a wonderful example of the fruitfulness of conducting cognitive neuroscience informed by evolutionary theory," said Todd Shackelford, a professor of psychology at Florida Atlantic University.

"I am hopeful that other researchers in the cognitive neurosciences will follow Dr. Platek's lead and take full advantage of the predictive power of a Darwinian perspective on the design of the structure of the mind," he told Discovery News.

It's likely, he explained, that a face we perceive as "friendly" is one that looks more like us. But how we later feel about that person could be tied to how we feel about ourselves, perhaps explaining the prevalence of arguments during family reunions.

© 2012 Discovery Channel

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