Why can saturated fatty acids pack tightly together forming solid fats?

Saturated fatty acids adopt the alternating all-anti conformation, which gives a maximum of symmetry to the crystal,

Explanation:

From the chemical point of view, they are very little reactive. They usually contain an even number of carbon atoms. In the nomenclature of fatty acids, trivial names are used more frequently than systematic ones. The abbreviated nomenclature is very useful for naming fatty acids. It consists of a C, followed by two numbers, separated by a colon. The first number indicates the length of the hydrocarbon chain, while the second number indicates the number of double bonds it contains.

The most abundant saturated fatty acids are palmitic (hexadecanoic, or C16: 0) and stearic (octadecanoic, or C18: 0). Saturated fatty acids of less than 10 C atoms are liquid at room temperature and partially soluble in water. From 12 C, they are solid and practically insoluble in water. In the solid state, saturated fatty acids adopt the alternating all-anti conformation, which gives a maximum of symmetry to the crystal, so the melting points are high. The melting point increases with the length of the chain.

the fossil record provides evidence of a common ancestor to many species.