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Why Alien Species Thrive
planux writes "The Sacramento Bee has an interesting article about why invasive animal species thrive, pushing out native species -- sometimes to the point of extinction. Kevin Lafferty, a U.S. Geological Survey marine ecologist at the Western Ecological Research Center in Santa Barbara says "Invasive species end up with about half the parasites, or diseases, they had at home." Animals with an average of 16 parasites on their home turf typically bring about three of the parasites with them to new locations. And only about four new parasites will typically adapt to attack the invading species. Net gain: 9 fewer parasites!"
If you're somewhere that has access to Nature's archives, you can read the two original articles this one was based off of:
Release of invasive plants from fungal and viral pathogens and
Introduced species and their missing parasites
I just checked, and marijuana (from the hemp plant) apparently was cultivated thousands of years ago in central asia (yes, China), then made its way west to Europe. It was imported (alien species!) to the New World very around 1600, as the hemp provided valuable fiber. I saw the stuff growing wild many feet tall in Asia, which was kind of startling. The varieties grown for drug use has been refined to have many times the THC of the wild variety. The US prohibits growing low-THC hemp for the idiotic reason that it makes law enforcement look bad. Soem argue it does have economic value.
Don't ask me to connect pot and natural selection....
Sickle cell is oh-so-nasty, and even the heterozygotes show some mild symptoms. Yes, I learned the same thing sickle cell and malaria. Only a fraction (8-45% by region) of Africans have the trait, so probably people with it simply survive somewhat more often. I guess it was a glitch at some point that helped, but was not do-or-die essential to survival.