It relates to a gene called Prdm9 (Science, vol323, p373) which has the claim of being the most rapidly evolving gene in human history.
Far from being a random event, it has been revealed that 80% of crossing over events occur at hotspots of recombination and 40% of those hotspots have the same 13 letter DNA sequence and the gene responsible for activating those 13 letter hotspots is the gene Prdm9. This gene is discussed within the article.
Also, did you know:
Some populations do more crossing over than others. Low levels of recombination are found in people of African descent who are more genetically diverse than Europeans anyway.
Men and women may have different combination strategies too (Nature, vol 467, p1099). In women crossing over tends to occur between genes which produces new combinations of genes.
In men crossing over is more likely to occur within introns so producing new versions of existing genes. No one knows why the sexes have different strategies but it sure is fascinating.