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   You may be your germs: Microbe genes slipped into human DNA, study says    
      
   By Ben Brumfield, CNN    
   Updated 9:04 AM ET, Fri March 13, 2015    
      
      
   The biggest collection of the human body's 100 trillion or so microbes is   
   in our gut.    
   The biggest collection of the human body's 100 trillion or so microbes is in   
   our gut.    
   Story highlights    
   Microbes in our bodies greatly outnumber our human cells    
   In millions of years, microbe DNA has slipped into cells, diversifying our   
   evolution, scientists say    
   (CNN)Evolutionary diagrams usually connect humans and monkeys with common   
   primate ancestors, but now, scientists say there's a missing link that   
   deserves a spot on that family tree -- our bacteria, fungi, and viruses.    
      
   Though most of our genes come from primate ancestors, many of them slipped   
   into our DNA from microbes living in our bodies, says British researcher   
   Alastair Crisp.    
      
   It's called horizontal gene transfer. Scientists have known of examples of   
   this for a long time: Bacteria slip genes to each other, and it helps them   
   evolve. And scientists have seen insects pick up bacterial genes that allow   
   them to digest certain foods.   
       
      
   An artist's rendering shows a DNA double helix.    
   An artist's rendering shows a DNA double helix.    
   Some researchers have disputed that microbes have swapped genes with the cells   
   of complex animals, such as humans. But a new study at the University of   
   Cambridge indicates it has probably happened a lot.    
      
   Humans may have as many as hundreds of so-called foreign genes they picked up   
   from microbes.    
      
   "Surprisingly, far from being a rare occurrence, it appears that (horizontal   
   gene transfer) has contributed to the evolution of many, perhaps all, animals   
   and that the process is ongoing, meaning that we may need to re-evaluate how   
   we think about    
   evolution," Crisp said.    
      
   Chock fulla microbes    
   That may not surprise microbiologists.    
      
   We humans and other complex animals are full of microbes, gajillions of them.   
   People have so many that microbe cells living in our bodies outnumber our own   
   vastly.    
      
   A body has about 10 trillion human cells, says microbiologist Rob Knight. The   
   microbe cells living inside of us number around 100 trillion. That's a ratio   
   of 10 to one. The biggest collection is in our gut.    
      
   They're mostly helpful, and we we'd have a hard time living without them.    
      
   Their genetic material dwarfs ours. The human genome adds up to 20,000 genes.   
   The collective genomes of the many varieties of microbes in our bodies adds up   
   to between 2 million and 20 million, Knight says.    
      
      
   It's no wonder that some them probably have been seeping into our DNA over   
   millions of years. It has helped diversify our evolution, the Cambridge   
   researchers say.    
      
   Fly, worm, human    
   In recent decades, scientists laid down genomes -- a detailed description of   
   gene sequences -- for all kinds of species, including humans.    
      
   The Cambridge researchers compared the genomes of various species of fruit   
   flies, worms and primates, including humans.    
      
   They calculated similarities and differences between the genes across those   
   species to look for ones that stuck out as not being part of a smooth   
   evolutionary lineage, but instead probably popped in at some point.    
      
   They found 128 formerly unidentified "foreign" genes in humans and confirmed   
   17 that had previously been reported. Most of them play a role in digestion.   
   But the scientists also found that the gene that determines blood types -- A,   
   B and O -- is "foreign.   
   "    
      
   Some "foreign" genes that transferred in from microbes help our bodies' immune   
   systems defend against microbial infections like bacteria and fungi.    
      
   The researchers said there may be an obscure chance that the "foreign" genes   
   got into our DNA a result of evolutionary happenstance, but they also said   
   theirs is the most logical and likely explanation:    
      
   The microbes did it.    
      
   http://www.cnn.com/2015/03/13/health/microbe-genes-human-dna-evolution/   
      
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