From dragging mates around by their hair to finding nutrition by hunting and gathering, men weren’t always the sophisticated and rational up-right beings that they are now. Life on earth has been evolving for the last three billion years, bringing important changes not only for those being dragged around by their hair, but for every species on earth.

Charles Robert Darwin was the first to formulate a theory of evolution by means of natural selection. His book, On the Origin of Species, was published in 1859, and has grown to be the underlying principle for every field within the life sciences, explaining the diversity of life on earth.

Brian Langerhans , associate professor of biology at N.C. State, specializes in evolutionary ecology, and thus relies heavily on Darwin’s theories in his everyday work.

“Every single day [for me] is influenced by Darwin’s ideas in particular. Evolutionary influence is everything I do,” Langerhans said. “If you are involved in biology, period, evolution influences everything.”

Langerhans said he cannot imagine a world without Darwin’s theories. The fact that we rely on his ideas so heavily, when they were published more than 150 years ago, should show their significance.

“[I can’t imagine where we would be] without any theory of evolution—that’s just totally impossible,” Langerhans said. “It’s impossible to know what it would be like because of the significant impact his ideas have had on all aspects of human life. He’s impacted how we eat, the medicine we take, how we conserve and reserve and the way we understand the planet and ourselves.”

A few of Darwin’s contemporaries were pursuing similar theories of evolution, according to Langerhans , so scientists wouldn’t be too far off if his ideas hadn’t been published. But Darwin’s ideas specifically were unique because “he knew all of these little nuances within certain things [that most others didn’t],” Langerhans said.

The scope, magnitude and shocking specificity of Darwin’s ideas have given them world-renowned relevance that continues to influence discoveries today. “[Darwin], if he were here, would be totally amazed with things involving the molecular influences; we’re looking for types of selection using tools he could have never anticipated,” Langerhans said.

Darwin’s theories have been tested and refuted, only to be rebuilt again by the scientific community. “[A lot of] big, recent discoveries are pretty influenced by his ideas; it turns out so many of his ideas were actually correct. Man, he was sure right, more than he was wrong,” Langerhans said.

For example, Langerhans tries to understand the mechanistic causes of speciation . Darwin’s answer was natural selection. “I figure out how new species are formed, but we are actually coming to all these conclusions Darwin was,” Langerhans said. “We thought natural selection wasn’t generating new species, but the evidence is overwhelming and indisputable that it has been the driver of speciation.”

John Godwin, professor of zoology, agrees that Darwin’s theories are pivotal to any study of life on earth. “Nothing in biology makes sense except in light of evolution,” Godwin said.

These theories impact some of the most important scientific discoveries. For example, Godwin explained the importance of Darwin’s theories when evaluating certain aspects of human genetics.

“[In one case] we looked at conserve mechanisms— a conserve set of genes that regulate reproduction— because a condition was discovered where a human was unable to reproductively mature,” Godwin said. “Usually there is such strong evolutionary conservation of those mechanisms, so to understand things like that we evaluate the most basic levels of evolutionary and extraordinary construction.”

Evolutionary theories also allow scientists to learn things about humans from certain similar animals, such as rats. So in the case mentioned above, scientists could test and study rats to learn about these strange circumstances.

“The medical community is coming to a view that understanding how the body’s systems evolved can suggest important things about how to treat humans and avoid certain diseases,” Godwin said. “For example, why is it we are becoming increasingly heavy? Diabetes is becoming a huge problem…because we have shelves and shelves of Twinkies , when 10,000 years ago food was hard to come by.”

Godwin is currently using Darwinian theories to compare the human genome with that of the zebra fish in hopes of making discoveries about human anxiety disorders.

“What we are looking at is the expression of genes in key areas of the brain that we know are linked to stress and anxiety, and how these gene patterns differ between fish that are very nervous and those that are not,” Godwin said. “We see those differences in humans as well…so this is a nice animal for understanding how the brain is put together early in life, and how it is wired to be more susceptible to certain disorders.”

Both Langerhans and Godwin celebrated International Darwin Day. Langerhans will be putting up annual birthday congratulations to Darwin on his website.