Each creature in PixArk have their own base value for every stat. Creatures in level 1 will have the exact stat as their base value. Each time a wild creature levels up, they will recieve a level up in a random stat. Wild Creatures recieve more stats from a level up than a tamed one.
For the health stat, the calculation works like this:
Wild level increase:
Base value health x 0.2
Domesticated level increase:
Newly tamed health stat x 0.0675 (1.35%)
Every time a wild creature levels up their health stat, they will add 20% of their base health value.
A gryphon level 1 will have 2400 health. If at level 2 it levels up the health stat, it will now get 480 extra health, which is 20% of 2400. Now the gryphon has 2880 health.
Each stat have their own multiplication factors:
Wild stat level up
Health: +20% from base value
Stamina: +10% from base value
Oxygen: +10% from base value
Food: +10% from base value
Weight: +2% from base value
Meele damage: +10% from base damage
Torpidity: +5% from base value
Domesticated stat level up
Health: +1.35% from newly tamed stat
Stamina: +10% from newly tamed stat
Oxygen: +10% from newly tamed stat
Food: +10% from newly tamed stat
Weight: +5% from newly tamed stat
Meele damage: +2.125% from newly tamed stat
When a creature is tamed, the domesticated stat increase will use the tamed stat (the stats it has the second you tame it, or is born from breeding) as a base value for calculating stat increase.
Let's say we tame a gryphon at level 20 and it has 150% meele damage. Now if we level up the damage stat, it will increase by 2.125% from 150, instead of it's base value like wild creature's stats are calculated. The meele damage should now be 153.1875%, rounded up to 153.2% (150 x 1.02125).
As you can see from this calculation, the higher a stat is before taming, the higher it will increase after taming too.