It is normally taken for granted by biologists that all biological inheritance (as opposed to cultural inheritance) is material and is transferred from one generation to the next genetically, in DNA, or is cytoplasmic inheritance (as in the case of mitochondria) or as epigenetic modifications of the DNA. However there are many problems with this seemingly straightforward view, not least the missing heritability problem. Through analysing tens of thousands human genomes, the attempt to find genes 'for' various physical traits and disease-proneness have been remarkably unsuccessful, except in the case of a few rare hereditary diseases like cystic fibrosis and sickle cell anaemia. Instead of accounting for about 80% of inheritance, the genes seem to explain only 5 - 10%. The remaining unexplained inheritance is called the 'missing inheritability' problem. The biologist Rupert Sheldrake has proposed an alternative hypothesis according to which most of the inheritance of form and behaviour depends on morphic resonance rather than genes. For a detailed discussion of his ideas see his book The Presence of the Past or for a briefer summary of the issues of these fundamental questions see Chapter 6 of his book Science Set Free/The Science Delusion.