All animals, birds, fish etc. are divided into sexes but there is a very big difference between all of them and humans. They were all created at the same time, male and female. Each was created independent of one another. Each can carry out its mission in life without the other one. The only need in their uniting is to breed. However, humans were created one as part of the other. The woman is עזר כנגדו. Their lives are unfulfilled without one another.
A man is to work hand in hand with his wife to fulfill their joint mission. He cannot do this alone. The expression ודבק באשתו , he shall cleave to his wife, is only stated by humans.
This unity takes place when both invest their minds, emotions and spirit to to be subordinate to and directed by a Higher Will. Together they form אדם.
Beraishis 2:24, Pages 69-70
