The type of reproduction that causes variation in organisms is sexual reproduction.

Here's why:

* Genetic Recombination: During sexual reproduction, two parents contribute genetic material to their offspring. This leads to the mixing and shuffling of genes, creating unique combinations that are different from either parent.

* Independent Assortment: During meiosis (the process that creates gametes), chromosomes are sorted randomly into daughter cells. This ensures that each gamete receives a different mix of chromosomes from the parent.

* Crossing Over: During meiosis, homologous chromosomes (one from each parent) exchange genetic material. This swaps segments of DNA, further increasing genetic diversity.

Asexual reproduction results in offspring that are genetically identical to the parent. While there may be occasional mutations, asexual reproduction does not involve the mixing of genes and therefore does not introduce significant variation.