Darwin theorized that mankind (both male and female) evolved alongside each other over millions of years, both reproducing after their own kind before the ability to physically have sex evolved. They did this through asexuality (without sexual desire or activity or lacking any apparent sex or sex organs). Each of them split in half: Asexual organisms reproduce by fission (splitting in half).
Every song has a composer, every book has an author, every car has a maker, every painting has a painter, and every building has a builder. So it isn't irrational to take this simple logic a little further and say that nature must have had a Maker. It would be irrational to believe that it made itself.
In the past, missionaries have traveled to far countries with the message of the gospel - with great hardship and often with the loss of life. In contrast, we can reach millions instantly from the comfort of our homes by merely hitting the 'send' button on our computers, or with iPads, or phones.