Odorant receptor genes in humans

The sense of smell is highly sophisticated in vertebrates but Homo sapiens ranks low in olfactory performance when compared to other species - why? Olfaction initiates with the interaction of odorants with specific receptors on the surface of olfactory sensory neurons in the nose. The genes encoding odorant receptors form the largest family in the vertebrate genome, numbering as many as 1000 in rodents. It has recently come to light that the repertoire of human odorant receptor genes, unlike in other vertebrates, is riddled with pseudogenes.