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Nearly half (49 percent) of the "nones" in the survey reported leaving religion because they just don't believe in it.

One fifth (20 percent) of the "nones" said they rejected their childhood religion because they dislike the organization itself.

If those two reasons seem natural and almost self-explanatory, the third explanation is where it really gets interesting.

Perhaps the most surprising cohort of the religious "nones" are the "inactive believers." They account for 10 percent of those surveyed: 8 percent described themselves as "non-practicing," and the other 2 percent said they were just "too busy." This group included zero atheists and only 3 percent of agnostics.

They never thought about it

They Don't Want To Change

They don't feel not Courageous

Their environment is holding them back

They feel like giving up after one or three failures

They Have Not Felt Enough Pain As yet

Two members of the same species combine their DNA to produce a new genome.

Some of their offspring will carry a beneficial mix of good genes from both parents, meaning they will respond better to environmental stresses that would leave asexual species in grave danger.

It is a "learning" process – an organism "learns" new information, especially in a changing environment, and the organism passes those lessons on (in its DNA) to the next generation to help them survive.

Darwin suggested that natural selection was not the only evolutionary pressure at work in sex. There was something else going on as well, something Darwin called sexual selection. This is a preference by one sex for certain characteristics in individuals of the other sex.

A study published in 2015 found that it is vital for males to compete for reproduction and females to choose between those competing males.

This helps explain why sex persists as a dominant mechanism for producing offspring.

A fossil called Bangiomorpha pubescens is a multicellular organism that sexually reproduced, the oldest reported occurrence in the fossil record.

The evidence that these fossils sexually reproduced is in the finding that the spores or reproductive cells they generated came in two forms – male and female. Today we know that red algae lack sperm that actively swim. They rely on water currents to transport their reproductive cells, which is likely how they have been doing it for the last 1.2 billion years.