Why Lord Brahma married his own daughter Saraswati???

According to our Purana, Lord Brahma was born in a golden springs from Lord Vishnu’s naval. Brahma had just taken birth and is a child without any knowledge. Brahma is considered as the creator of our universe.

Brahma, for the hep in the process of creation, created a female deity called Shatrupa also known as Sandhya or Saraswati(the goddess of knowledge). He was so attracted to her beauty that he tried to constantly look upon her. Although Brahma had refrained from all sorts of senses but somehow his mind slipped this time and felt desired for Saraswati in his heart. Saraswati, whereas, was not pleased with this behaviour of Brahma and was trying to hide in all possible directions from his gaze.

Brahma grew extra heads for every direction she was going. He grew four heads in four directions. To escape from Brahma she went up into the sky hid herself. Brahma grew a fifth head upwards and found her. Every time she hid herself Brahma was able to find her. Devi Saraswati became angry and hopeless.

Lord Shiva, seeing the obsession of Brahma towards Saraswati, got furious and punished Brahma by cutting his upward head and also Lord Shiva cursed him for not being worshiped by anyone due to his act towards Saraswati.

Saraswati found herself helpless and finally she surrendered to Brahma for the purpose of creating life. They spent around 100 years together and there gave birth the Manu, the first man in the universe.