On a trip to the Galapagos Islands as a young man in 1835, Charles Darwin made some keen observations that, little did he know, would change the course of science forever.
Over the next two decades, he continued to observe how organisms had traits that seemed to be very well-suited to their environments, even though there were similarities between species in different environments. He decided this must have arisen from small changes in animals over time that caused species to evolve.
In 1859, he published On The Origin Of Species, which introduced the idea of evolution through natural selection. (Although, curiously, he never actually used the word "evolution" in the book.) It shook the world irrevocably, and we are still feeling those aftershocks today.
Each year on Darwin's birthday — now known as Darwin Day — scientists remember his incredible contributions.
In honor of Darwin Day, here are corrections to 7 popular misconceptions about the theory of evolution.
Misconception 1: Humans couldn't have come from monkeys, because there are still monkeys.
While "The Evolution Of Man" graphic showing progressive stages of human evolution is nice, it's an extremely simplified version of how humans came to be.
Evolutionary biologists do not believe that humans came from monkeys. Rather, humans are apes and share a common ancestor with chimpanzees.
About 6-8 million years ago, there lived a species in African forests that scientists have dubbed Pan prior. Over time, two subgroups emerged: those that stayed in the trees, and those that spent more time on land. By living in two completely different environments, each group had different food availability and faced different challenges.
Over many generations, the group on the ground slowly developed the ability to walk upright, as crossing flat land on two legs instead of on all fours was faster and less energetically taxing. Those that had the ability to walk upright had a distinct advantage. Genes associated with bipedality gave some individuals a better chance to survive and reproduce. Over time, these genes were selected for and persisted throughout the population.
In contrast, those ancient apes that didn't leave the trees had little to no incentive to walk upright, so that trait was never selected for.
Though both groups came from the same place, adaptations molded modern humans and chimps to be very different.
It's easy to see how silly this misconception is by simply asking: "If we came from our grandparents, why do our cousins exist?"
Misconception 2: Evolution is "just a theory."
The biggest problem with this misconception is that while many people use the word "theory" to describe something that is a hunch or a guess, in the scientific community, a theory is so much more.
What makes this especially confusing to some is that there is a difference between scientific theories and scientific laws, but one is not more true than the other. A scientific law applies when something happens the same way every time it is tested. "What comes up, must come down," describes the law of gravity, but it doesn't give us much other information. On the other hand, the theory of gravity attempts to explain what the force of gravity is, how it works, and how it can be tested.
A scientific theory has four key criteria it needs to satisfy: It needs to explain a body of facts, it should predict future outcomes based on what has been seen previously, it needs to be testable and have an ability to be proven wrong, and it needs to be supported with evidence.
Evolution fits all of these beautifully.
Misconception 3: Certain things, such as the human eye, are too complex to have evolved.
Some deniers of evolution claim that the eyeball is too complex to have come about through generations of subsequent mutations. But the way light enters the eye and goes through the retina before being processed by the brain is backward. Complex, yes, but it is far from ideal.
Many other organisms have eyesight that is far poorer than humans, with some possessing not more than a light-receptive patch. Some vision is better than none, and this clearly explains why this trait would have been an advantage. Over time, small photoreceptive patches eventually became more complex structures.
Additionally, there are many animals that have eyesight far keener than ours, giving them the ability to see more colors, farther distances, and sharper details. There are many different kinds of eyes in the animal kingdom, each of which evolved to adapt to a unique environment.
Misconception 4: Scientists are searching for the "missing link" between chimps and humans.
Evolution is not linear, with one link feeding neatly into the next. There is no clear division when speciation occurs.
While a daughter might look similar to her mother, who looked like her mother, there might not be as strong a resemblance between grandmother and granddaughter. If the granddaughter was compared to an ancestor who lived 300 years ago, there would likely not be any indication they were members of the same family. Going back 300,000 years or 300,000,000 years, however, we wouldn't even find a member of the same species, despite having a direct lineage.
In the middle, individuals would show traits of both species. During speciation events, there an incredible amount of hybridization occurs. In addition to all of this genetic confusion, the fact that fossilization is so difficult adds another layer of complexity.
While the fossil record is tremendous, there aren't fossils of every organism that ever lived. In order for an organism to fossilize, it needs to die in a favorable environment, typically buried by sediment. Minerals in the sediment replace the minerals lost in the bone during decomposition, eventually turning it into a fossil.
Because not everything died in this way, scientists may never have a set of bones they can point to definitively as the last common ancestor, but there's already more than enough evidence to support the familial link.
Misconception 5: Microevolution might exist, but it cannot happen on a larger scale to change entire organisms.
Some of those who won't accept evolution will concede that there is microevolution, in which a species can undergo small genetic changes, such as bacteria evolving a resistance to certain drugs, or a particular hair color becoming more common in a certain population. But they refuse to believe that a species can change into something else.
Macroevolution is simply an accumulation of microevolution events. Generation after generation, genetic mutations occur and impact how species look, act, and eat.
There is no clear boundary between macroevolution and speciation. There is no "first" of a brand new species. Each offspring is slightly different from its parent, but sometimes those differences can't be noticed until tracing a lineage for quite some time.
Misconception 6: Scientists argue about whether or not evolution is real. Therefore, teachers should not discuss it in class.
While scientists might argue over certain aspects of evolution, such as what the fossils indicate about a particular organism's diet or how they moved, there is no debate about the fact that evolution as a whole is real.
A study found that 99.9% of life scientists accept evolution by way of natural selection, clearly proving that controversy on the subject is manufactured and is political, not scientific, in nature.
Teachers are given the job of explaining things to students using facts. Evolution absolutely must be taught in classrooms. Because it is true.
Misconception 7: Darwin admitted evolution was a lie on his deathbed.
It has become a popular myth that just before his death, Darwin admitted evolution wasn't real. Not only did this not happen (according to his children, who were there), but it wouldn't have mattered if he did.
Charles Darwin was able to come up with a beautiful theory based solely on observations. He never knew of Gregor Mendel's pea plant experiments that would serve as the basis of the field of genetics, the mechanism for evolution.
The fossil record at his time was very sparse. He had no knowledge of how geology would be used to explain how long ago something lived or how rocks could contain evidence of mass extinction events, such as the iridium that helped solve what happened to the dinosaurs.
Considering how much Darwin didn't know, it's astounding how correct he actually was. Since his death, scientists have learned more about evolution and refined his theory to reflect this body of new information, but his original idea is at the very heart of it.
These days, scientists don't just use evolution to understand what lies behind us, but to propel us into the future as well. Understanding evolution is critical to making effective treatments against bacteria and viruses. It's helping doctors understand how cancer acts the way it does. It is critical to managing the conservation of endangered species.
We owe so much to the young man in the Galapagos who made a curious observation and dared to explain why it was so.
Cover image: Peter Macdiarmid / Getty Images