Life - This dictates how much damage you can take before death.
Defense - How much Attack damage you soak, the higher it is the less life you lose on hit.
Stamina - How often you can dodge. The higher it is, the more dodging you can do, without worrying about being hit.
Hunger - How long you can go without your need for meat or plants starts draining your life. The higher it is the longer you can go without, however you will need more food to fill you up.
Speed - How fast you move. The faster you are the better to escape threats or catch food. (The only way to temporarily alter this stat is to wear the full Aviator set unlocked by the Thoroughbred Horse, or the Tuxedo.)
How to gain stats?
By completing challenges you gain TEMPORARY stat boosts (such as Hunger +5). When you die or advance generations you lose these stats.
To permanently boost stats you need to first get temporary stat boosts, then find a Mate (the higher Rank mate the better). When you advance a generation, you lose your temporary boost, however a percentage of them (determined by the quality of your mate) are kept.
For example, if you completed three challenges and got Attack +5, Life +10 and Hunger +2, then mated with a prime mate, After mating you will see a notification saying you have Attack +3, Life +5 and Hunger +1. It means you lost some of the buffs from the challenges, but kept 3 Attack, 5 Life and 1 Hunger, for every generation to follow.
(A prime mate keeps 50% of these buffs, an average keeps 25%, and a desperate mate keeps only 10% of these buffs. [