Nature Teams with Nurture: A resurrected perspective on inheritance and evolution
By Michael Whaby
"I think there can be little doubt that use in our domestic animals strengthens and enlarges certain parts, and disuse diminishes them" — Charles Darwin
The age-old debate, nature vs nurture, is being re-evaluated. Although DNA lays the foundation for who we are, experiences mold our behaviors throughout our lifetimes—but do these experiences actually have the capacity to affect successive generations? A new perspective on evolution and inheritance is coming to fruition, and many are taken aback by the emerging, dogma-shifting evidence.
The term, survival of the fittest, is no stranger to the common ear. This term originated from Charles Darwin’s theory of evolution: natural selection. Under this theory, organisms that are most fit for their environments are selected for and reproduce at more successful rates. These successful organisms out-compete other organisms, in this regard, by keeping their DNA around—by reproducing, of course—and, in fact, that DNA, which is essentially every organism’s unique blueprint, is actually the basis for their success, or fitness.
Jean-Baptiste Lamarck’s theory of evolution might be a bit more foreign to the common ear but is nonetheless becoming increasingly more omnipresent. Lamarck’s theory is often referred to as the inheritance of acquired characteristics. You probably learned of an example of this and, subsequently, of its rebuttal: Giraffes once had short necks, but over time, after many frustrating attempts to stretch their necks and eat from tall trees, they acquired longer necks. This mechanism is referred to as use and disuse—passing on to offspring traits that are useful while discarding those that are not (as even Darwin mentioned in his book, On the Origin of Species, as quoted above).
As you see, both theories of evolution yield changes in organisms; however, one happens through means of sheer changes in DNA, while the other seems, well, less transparent. To understand both of these forms of evolution, you must grapple with two concepts: genetics and epigenetics. Genetics deals with DNA and changes within it. Epigenetics—as the prefix epi- suggests—deals with changes on, but not within DNA. As an analogy, genetics is the machine (DNA) while epigenetics are the workers turning the machine on and off.
Notice how DNA was not mentioned once in the explanation of Lamarckian evolution. That is because changes in the genetic code—the actual DNA—are not required for this evolution to take place. The basis of Darwinian evolution, however, revolves around changes in DNA, and how these changes may or may not make an organism more fit for their environment.
Today, we have a solid understanding of genetic inheritance, and we even use these understandings to track, prevent and, astoundingly, cure genetic diseases. For example, a rare neuromuscular disease, Spinal Muscular Atrophy, is caused by the genetic inheritance of a single mutation in DNA—keep in mind that there are approximately 3 billion units of DNA in the human genome. This disease, as of 2019, has a cure that saves infants that would otherwise die by the age of two! Our understanding of epigenetics, and its inheritance, however, is not as solidified, but current work is being done to unravel its mysteries.
Some pivotal research regarding epigenetic inheritance, carried out by Brian Dias and Kerry Ressler at Emory University School of Medicine, was published in the scientific journal Nature Neuroscience. They showed that mice conditioned to react to a particular odor—the “odor-conditioned mice”—can indeed pass down information that makes even their offspring more sensitive to the same odor. They proved this by showing that the offspring of the odor-conditioned mice, and even their offspring’s offspring, had more olfactory (nose) neurons specific to that odor compared to mice whose parents were not exposed to the odor. This evidence suggests a mechanism for parents to pass down “important” information—without changing DNA—to their offspring that is likely to be useful in their lives.
So, what is the significance of this? We already know that the environment can influence genetics as well as epigenetics—UV from the sun can damage DNA (genetics) just as exercise can cause changes in how DNA is used (epigenetics). But maybe the implications of epigenetic inheritance should perhaps carry equal importance to genetic inheritance. For instance, how much does the lifestyle of the parent, prior to conception, really matter? What are the risks associated with, say, one parent being an alcoholic? Will the conditioned habits of parents have any effect their children, as the odor-conditioned mice passed on information to their offspring? We, and every other organism, don’t have much control over the DNA that our offspring receive, as this is an inherent process. But maybe we have more control than we think about how our epigenomes are passed on.
Dias, B. G., & Ressler, K. J. (2014). Parental olfactory experience influences behavior and neural structure in subsequent generations. Nature neuroscience, 17(1), 89–96. https://doi.org/10.1038/nn.3594
Lacal, I., & Ventura, R. (2018). Epigenetic Inheritance: Concepts, Mechanisms and Perspectives. Frontiers in molecular neuroscience, 11, 292. https://doi.org/10.3389/fnmol.2018.00292