So your kid wants to know how babies are made? Don’t hem and haw or spin some yarn about birds and bees—break down the biochemistry. It’s true what they say: The sexiest organ is the brain.

1/ Attraction

When a mommy and a daddy love each other very much, the neurons of the ventral tegmentum start producing the neurotransmitter dopamine and pumping it to the caudate nucleus, the hypothalamus, and other brain regions. High levels of dopamine can induce the release of testosterone, which is associated with a drive to make babies.

2/ Arousal

For daddies, physical and/or visual arousal can cause the neurotransmitter nitric oxide to be released by the autonomic nervous system. The chemical boosts the blood flow into the corpora cavernosa—the spongy tubes in the penis. As they inflate, the veins that would normally drain the blood are squeezed shut. Nitric oxide probably also causes clitoral swelling.

3/ Stimulation

Sexual stimulation triggers nerve cells in the brain to release stored oxytocin into the bloodstream. The hormone stimulates contractions in the smooth muscles of the uterus and of the male reproductive system, increasing enjoyment for both participants. In men, the theory goes, the contractions ultimately assist with ejaculation.

4/ Consummation

The climax phase of the sexual cycle triggers the release of more dopamine into the nucleus accumbens. (Known as the “reward area” of the brain, the accumbens is also associated with addiction.) Doing the deed also produces more testosterone. This can, in turn, result in a repetition of the act. Unless Mommy and Daddy have to get up early the next morning.