what does this quote mean "The woman is the mule of the world." Nanny

Janie's grandmother is a former slave who represents the thoughts and fears of the men and women of the slave era. Nanny values wealth and security over anything else and too strongly encourages Janie to marry Logan Killicks because he possesses some land and a mule. Nanny feels that negro women are relegated to being treated like mules so she might as well marry man with some land and a little money.