Nicky taught a lesson on variation in species as part of the IGCSE Biology and Double Science curriculum, covering genetic, environmental, and combined variations, along with concepts of random fertilization and mutations. The session included practical examples of genetic diagrams and Punnett squares to demonstrate allele combinations and probabilities. Nicky explained how both genetic factors like mutations and environmental influences contribute to variation, while also introducing the concept of natural selection and concluding with a review of mutation definitions.