Republican presidential candidate Ben Carson compared allowing gay and lesbian couples to marry to requiring that car seats accommodate conjoined twins and anatomically normal children.

Carson made the analogy in his latest book, titled A More Perfect Union.

“Laws and regulations should be designed to address normal situations while providing special mechanisms for the creation of exceptions in abnormal situations. Changing the law governing the normal situation in order to accommodate the abnormal situation is like requiring that car seats be designed to accommodate conjoined twins as well as anatomically normal children,” Carson wrote.

“The more sensible thing would be to require car seats to accommodate typical children and design special car seats for atypical children as needed. This principle can be applied to a host of situations in our nation. For example, most people are heterosexual, and changing the definition of marriage to suit those outside that definition is unnecessarily complicated.”

Earlier this year, Carson vowed to no longer discuss LGBT rights after being widely criticized for claiming that being gay is a choice because prison can make a person gay.

(Related: Ben Carson won't say whether Gay Pride flag symbolizes “hatred toward Christians.”)