The genomic structure defines both physical and psychological human characteristics. It can be safely conceived that genomes define also a 'mental' representation of the psychophysical characteristics – the idea - of the partner, the ideal one required to achieve the expected selection of the perfect couple (for evolutionary purpose?). This mental picture of the ideal partner – this idea - can be called Ideal Partner Idea (IPI). The genomic determined IPI is molded by personal achieved culture.

Hypothesis on the mechanism of couple choice and love
The real appearance of persons – saying their specific, visible psychophysical characteristics – is called here General Appearance, GA.
When persons come together, each one compares GA of the others with his proper IPI. The result of the comparison depends from the real degree of similarity between personal IPI and the GA of attendants, together with the cultural ability of each subject to make an efficient comparison. The degree of similarity between the IPI and GA of the subjects is strictly related to the probability for a resulting degree of pleasantness between the two and in the end - if the similarity between IPI and GA is high enough - the probability to fall in love.
The result of the comparison is not strictly linked neither to similarities nor dissimilarity of GA with characteristics of the physical aspect and/or personality of individuals as it is a-priori chosen by single individuals.
The falling in love of a single person having the IPI very similar to the GA of a second person is not a guarantee for the two to live together with success.
The formation of a couple in love requires that the IPIs of the two individuals too would compare favourably.
The result can be expected to occur with quite high probability, if the relationship of personal GA and personal IPI is of such a kind that – putting GA1 and IPI1 the characteristics of a first person, and GA2 and IPI2 the ones of the second one – the genomic-and-cultural conditions leading to IPI1 would correspond with GA2 and viceversa IPI2 correspond with GA1.
According to the degree with which the idea of ideal partner of the two individuals corresponds with general psychophysical characteristics of the other, then the encounter of the two persons will be:

  GA2 <similar to> IPI1    and    GA1 <similar to> IPI2

The higher the similarity between respective IPI and GA, the higher can be expected the probability of pleasantness and mutual love will be.

Taking into account the diversity of individual psychophysical characters as determined by action of genomic-and-cultural events, a large possibility do exist for encounter of different IPI and GA, leading to different degree of similarity of Idea (IPI) with reality (GA) of psychophysical characters. Accordingly, the probability for different individuals to develop different degrees of pleasantness and in the end – but also at first sight - to fall in love, it will be.