Lamarckism (and some Epigenetics)

     Lamarck focused on the individual organism and the changes in traits that occurred through its life. He believed the changes in the individual would affect its offspring. Darwin focused on the changes of traits within a population, and he believed that trait changes took place over the many generations. Darwin believed that all organisms had a common ancestor, while Lamarck believed that all organisms had independent origins. Lamarck also believed that an organism can take the initiative to change it’s own characteristics, its own behavior and physical traits, to better adapt to its environment and survive. He then believed that these changes would be heritable to the organism’s offspring, and the offspring could continue to enhance these changes during the course of its life. 

Lamarck did get one aspect right, which is that traits are heritable. Heritability is an important aspect of evolution. If parents were unable to pass on the traits that made them better survive in their environments, then the traits the offspring possessed would be random. This would likely result in more deaths or less reproductive potential / fitness in the population, thus drastically decreasing population size and genetic diversity. Lamarck was incorrect in the notion that organisms could change their own characteristics during their lifetime and pass those characters on. 

Darwin’s evolution through natural selection states that organisms in a population have a degree of genetic diversity and thus some are born with slightly different traits. The traits that are more conducive to their environment and thus help them to better survive, gain resources, and reproduce. If they are better adapted to their environment, then they have a better ability to reproduce and reproduce more, thus increasing their genetic fitness. Their offspring will have these traits and will also be better suited to adapt to their environments. The genetic frequency and thus phenotypic frequency of the population will likely change because the better adapted organisms will provide more offspring, thus increasing the frequency of their genes. The other organisms within the population that do not have the “better” trait will not reproduce as much and may even die, thus reducing the frequency of their genes and phenotypic traits. In short, genetic diversity and random mutations give organisms the ability to capitalize on new genes/traits that better aid them in their environment.

Lamarck’s theories of individual change, as opposed to population change, reminds me of the concept of epigenetics. Researchers have discovered that by altering behaviors/habits/lifestyle, humans can more or less change how often or how much their genetic code is read, thus shutting off / turning on their own genetic code. These are known as epigenetic changes. The genetic code itself is not altered. Molecules, like methyl groups, are only added or taken away, and histone groups can be furled tightly or loosely based thanks to the absence or presence of acetyl tags. This affects gene expression. When it comes to heritability, most epigenetic changes that occur are erased after fertilization. However, not all epigenetic changes may be undone, so some epigenetic factors may be passed on to offspring. The lifestyle and habits of a person may affect their children! The first time I learned about epigenetic was from watching this video, and it blew my mind.

Sources

Trerotola, M., Relli, V., Simeone, P., & Alberti, S. (2015). Epigenetic inheritance and the missing heritability. Human genomics, 9(1), 17. https://doi.org/10.1186/s40246-015-0041-3