Proving Horizontal Gene Transfer in Humans (2/15/2007)

Darwin's theory of natural selection is considered by most scientists to be correct, the mechanism that allows it to occur has been hard to nail down though. Many scientists have claimed that it is the accumulation of minor genetic mutations over time. As new traits are developed they will be passed on only if the trait gives the bearer some advantage. The inverse of this is also true, in that if an organism inherits a trait like a disease, then they may not be around long enough to pass on the trait.

New evidence in genetics suggests that random genetic mutations aren't the only reason we inherit new traits.

In a recent paper about horizontal gene transfer (HGT), Dr. Michael Deem with Rice University shows that gene's are being transferred from one species to another. How the genes are being transferred though is still debatable.

In another paper by Dr. Sarah Tishkoff with the University of Maryland, she may have stumbled upon a potential clue. In her research on Lactose Persistence, she mentions the Hadza population of Tanzania who have the ability to digest lactose even though they are hunter/gatherers and don't practice cattle domestication. So how did they obtain the ability to digest lactose?

There are several possibilities:

1. it could be random mutation/recombination
2. sometime in there genetic past they did practice cattle domestication
3. some other gene or trait they have that is advantageous is bound to the lactose persistence gene
4. They are receiving the gene through some other source, such as HGT.

It is unlikely that it is just a random genetic mutations, considering such a high number of Hazda people that have the gene. They may have practiced cattle domestication in their genetic past, but this would be hard to prove. Their may also be some other gene that is dominant that is somehow linked to the lactose persistence gene, but this would require a much larger data set and possibly a complete genome of the Hazda.

What if it were horizontal gene transfer? First off, how does it work, how do the gene's get transferred from one organism to another. In similar species it happens through sex, but how does it work in different species? At the very least, the genetic information would need to be passed via blood, semen, or bodily fluids that contain all or some of the DNA being exchanged.

Virus's have been known to be transferred from food that wasn't cooked properly. If a virus can be introduced across species can DNA?

What if the Hadza have received this gene through something they ate? What if an animal they were eating had the lactose persistent gene? How would you test this theory?

I'd start by determining the specific type of lactose persistent gene that the Hazda have. I'd then determine what constitutes the bulk of the Hazda diet now and in the past. I'd focus on large mammals, specifically, since they are milk producing, and probably part of the Hazda diet, and their DNA would be the most compatible with humans. I'd then test the DNA of these animals for the lactose persistent gene.

If the specific lactose gene that the Hazda have is the same as one or more of the animals that they eat, then it is only circumstantial proof at best. The real proof would come from comparing the complete set o genes the Hazda have with the genome of eaten animal to determine if they share other genes. As a control group I'd use something completely foreign to the Hazda, perhaps a whitetail deer from the United States. If the Hazda have more genes in common with the animals they are eating than with the whitetail deer, then this would show fairly strong evidence that genetic information is being transferred from the eaten animal to the Hazda.

In another way you could test the lactose gene's being exhibited in other people, and determine if they are predominant in the animals they traditionally eat. If the lactose gene a person has is more abundant in the food they or their ancestors ate, than in other animals, then this would also show fairly straight forward proof that genes are being transferred.

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