In addition to founder effects, the new population is often a very small population and so shows increased sensitivity to genetic drift, an increase in inbreeding, and relatively low genetic variation.
The short answer for how long does it take to become a lawyer is that in the United States it takes a minimum of three years. In order to practice law anywhere in the western world, one must pass an examination in the geographic jurisdiction that the proposed lawyer wants to practice law.
There is really no shortcut on how to become a lawyer. You should have participated in relevant activities at the undergraduate level or interned at law firms over summer to make a compelling case of wanting to become a lawyer. After law school, you can take the bar exam to practice in particular states.