Mayonnaise and the origin of life

by Harold J. Morowitz

Mayonnaise is a mixture of oil and water. But we know that oil and water do not mix. What is the magic ingredient that allows us to mix salad oil and weak acetic acid (vinegar - mostly water)? It takes a special long molecule – an amphiphilic molecule, which has an affinity for water on one end and an affinity for lipids (oil) on the other. And what is the most common source of this amphilic molecule? Egg yolks, of course. Add some egg yolks to your salad oil and vinegar and blend carefully. Voila! Mayonnaise. (A bit of lemon juice helps the flavor.) Lecithin is the term you will find on many of your food products. Lecithin is an amphiphilic molecule. In fact, the word lecithin comes to us from the Greek *lekithos*, meaning egg yolk. The biological cells of our body have a wall that separates lipid from water. Before the evolution of amphiphilic molecules, no cell wall could exist. After the biological cell became possible, all evolution continued. From mayonnaise to life!