Children conceived during famines and mice with yellow coats have each clearly taught us remarkable things about early development, and the importance of epigenetics in this process. Oddly enough, these two disparate groups have one other thing to teach us. At the very beginning of the 19th century, Jean-Baptiste Lamarck published his most famous work,
Chapter 6. The Sins of the Fathers
For I, the Lord your God, am a jealous God, punishing the children for the sins of the fathers to the third and fourth generation of those who hate me
The
Kipling was having fun with his stories, whereas Lamarck was trying to develop a scientific theory. Like any good scientist, he tried to collect data relevant to this hypothesis. In one of the most famous examples of this, Lamarck recorded that the sons of blacksmiths (a very physical trade) tended to have larger arm muscles than the sons of weavers (a much less physical occupation). Lamarck interpreted this as the blacksmiths’ sons inheriting the acquired phenotype of large muscles from their fathers.
Our modern interpretation is different. We recognise that a man whose genes tended to endow him with the ability to develop large muscles would be at an advantage in a trade such as blacksmithing. This occupation would attract those who were genetically best suited to it. Our interpretation would also encompass the likelihood that the blacksmith’s sons may have inherited this genetic tendency towards chunky biceps. Finally, we would acknowledge that at the time that Lamarck was writing, children were used routinely as additional members of a family workforce. The children of a blacksmith were more likely than those of a weaver to be performing relatively heavy manual labour from an early age and hence would be likely to develop larger arm muscles as a response to their environment, just as we all do when we pump iron.
It would be a mistake to look back on Lamarck and only mock. We no longer accept most of his ideas scientifically, but we should acknowledge that he was making a genuine attempt to address important questions. Inevitably, and quite rightly, Lamarck has been overshadowed by Charles Darwin, the true colossus of 19th century biology – actually, probably the colossus of biology generally. Darwin’s model of the evolution of species via natural selection has been the single most powerful conceptual framework in biological sciences. Its power became even greater once married to Mendel’s work on inheritance and our molecular understanding of DNA as the raw material of inheritance.
If we wanted to summarise a century and a half of evolutionary theory in one paragraph we might say:
Random variation in genes creates phenotypic variation in individuals. Some individuals will survive better than others in a particular environment, and these individuals are likely to have more offspring. These offspring may inherit the same advantageous genetic variation as their parent, so they too will have increased breeding success. Eventually, over a huge number of generations, separate species will evolve.