Well-known atheist and best-selling author Richard Dawkins REUTERS/Chris Keane Scientist Richard Dawkins apologized on Thursday for causing a "feeding frenzy" on Twitter after he said it would be immoral not to abort a fetus with Down's Syndrome.

Dawkins, who has been at the centre of a series of controversies on social media, responded to a user who said they would face a "real ethical dilemma" if they discovered they were expecting a baby with Down's Syndrome.

"Abort it and try again. It would be immoral to bring it into the world if you have the choice," the biologist wrote.

The comment drew criticism from users of the social media site.

"I would fight til my last breath for the life of my son. No dilemma," one user replied.

In a later blog, the author of The Selfish Gene and The God Delusion said his comment had been "tactlessly vulnerable to misunderstanding".

"If your morality is based, as mine is, on a desire to increase the sum of happiness and reduce suffering, the decision to deliberately give birth to a Down baby, when you have the choice to abort it early in the pregnancy, might actually be immoral from the point of view of the child's own welfare," Dawkins wrote.