Conjoined twins Marieme and Ndeye Ndiaye seem to be as similar as any two people can be, physically and genetically, but to their dad, Ibrahima Ndiaye, says the 6-year-olds couldn't be more different.

Identical Twins Are Genetically Different, Research Suggests SAN FRANCISCO – Identical twins may not be so identical after all. Even though identical twins supposedly share all of their DNA, they ...

Behavioral and physical differences between identical twins are fascinating because they are unexpected. Many people assume that when identical twins differ they do so because they are treated ...

The Science of Siblings is a new series exploring the ways our siblings can influence us, from our money and our mental health all the way down to our very molecules. We'll be sharing these stories ...

Logically speaking, you would think that animals who appeared to be the same – even if they were found in different parts of the world – would belong to the same species, and that they would share the ...