OPTIONAL RULE
A skill adjustment is listed with some of the species. This is a reflection on the capabilities of the species. If a species is more physically or mentally capable, then they don't have to work as hard to accomplish their goals, and therefore will earn skill at a slightly slower rate. The species that are at a disadvantage will rely on earned skill more than the capabilities they were born with so they will earn skill at a slightly faster rate.
There are two ways that this adjustment can be used. Obviously, the first is when awarding skill to a character. When a character has earned ten skill, you would add the skill adjustment to the ten skill. In the case of a negative skill adjustment, the ten skill will go down and thus, the character will need to earn more skill to reach the next stage. The negative adjustment would only be added once per stage. In the case of a positive skill adjustment, the character would have skill added and thus have a head start on the next stage.
The second way the adjustment can be used is during character generation. Often when creating a character you start them off at second stage, or third stage, etc. But, you could add some variability to it. Let's say you want to start the character in second stage. You could say that their skill is 25 plus the species skill adjustment. This would keep them in second stage, but would make the capable species work a little harder to reach third. To add even more variability, you could add a dice roll. For example, roll 1D6, where a 4, 5, or 6 is an addition of 1, 2, or 3 skill respectively and 3, 2, or 1 is a negative of 1, 2, or 3 respectively. If you add the skill adjustment, it is possible that the character could cross a stage boundary in either direction.
Obviously, these are optional rules. They are used when the referee wants to inspire the players to pick species other than Groten, Massetin, etc.