Charles Darwin (1809-1882) first published this work in 1868 in two volumes. The book began as an expansion of the first two chapters of "On the Origin of Species: 'Variation under Domestication' and 'Variation under Nature'", and it developed into one of his largest works; Darwin referred to it as his 'big book'.
In volume 2, concerned with how species inherit particular characteristics, Darwin first published his 'provisional hypothesis' of pangenesis. This theory of 'gemmules' was not met with much acceptance and today is not valuable as scientific explanation, but it was important in laying down the key questions that needed to be answered regarding the processes of genetic inheritance. Darwin also used volume 2 to challenge the theories of evolution by design, expounded by the botanist Asa Gray. Darwin's arguments were some of the very first in a long debate that remains hot today.
13. Inheritance continued: reversion or atavism
14. Inheritance continued: fixedness of character, prepotency, sexual limitation correspondence of age
15. On crossing
16. Causes which interfere with the free crossing of varieties, influence of domestication on fertility
17. On the good effects of crossing, and on the evil effects of close interbreeding
18. On the advantages and disadvantages of changed conditions of life: sterility form various causes
19. Summary of the four last chapters, with remarks on hybridism
20. Selection by man
21. Selection continued
22. Causes of variability
23. Direct and definite action of the external conditions of life
24. Laws of variation, use and disuse, etc.
25. Laws of variation continued, correlated variability
26. Laws of variation continued, summary
27. Provisional hypothesis of pangenesis
28. Concluding remarks