Why is there always an Opposite?

Do you wonder why almost everything has its opposite? 

I do wonder why.

We have BLACK color and then there is also WHITE. You can choose to go Up or Down, or Left or Right. The world has NORTHERN part and SOUTHERN part, plus the EAST and the WEST. You can always turn ON and OFF your television set if your bored. In entering restaurants, you can either PUSH or PULL the doors. What is the difference between PROTONS and ELECTRONS or why does our batteries have POSITIVE and NEGATIVE charges. Sometimes you feel HOT then suddenly it feels COLD. Some trees are TALL and some are SHORT. Flowers and some plants can either be BEAUTIFUL or UGLY. The sun either RISE or SET.

In humans, why do distinctions between man and woman exist? 

Disclaimer: This picture was retrieved from http://www.faqs.org/photo-dict/phrase/2775/balance.html.

From the very beginning, our creator could have opt to design one mold. The mold which will bring in to existence similar and equal type of person. The question is why does He chose to create two distinct person. As for me, I see it as a way of God on how He wants to continue life on earth, to leave on the hands of the people how they will develop, adjust and balance out the world. Thousands of years ago, Men are always seen to be tough, hard and authoritative. Women, on the other hand, are sweet, helpless and subservient. The world back then are dominated by men. Men are SUPERIOR and women are INFERIOR. The concept of equalities does not exist. But as the world revolves and changes continues, the people also developed and learned to grow. In our modern world, equality was born and known all over.  Men learned to listen and to respect women. Our balance scale is now stable, but no one can tell if someday the scale may lean either to the left or the right. So if we know that we are one of the weights working as a balancer, let us just continue to live the way we have been living.