Arthritis
Arthritis is a joint disorder in
which there is inflammation of one or more joints. Arthritis is frequently accompanied by joint
pain. There are many types of arthritis and over 100 have been identified. The causes
of arthritis include injury, metabolic abnormalities, hereditary factors,
effect of infections, and a misdirected immune system. Arthritis is mostly
common among women and occurs as people get older. Severe arthritis can result
in chronic pain, inability to do daily activities and can cause difficulty in walking.
I would say immigration only.
emigration would theoretically reduce the genetic variation as unique individuals leave, but immigration would bring unique traits into circulation in an ecosystem.
I'm not super great at biogy tho so this might not be right... :)
