When explaining human origins, a staggering 42% of all Americans still ascribe to a creationist interpretation—despite the fact that there’s plenty of evidence to support the theory of natural selection. Here are some of the most potent scientific discoveries that prove Darwin was right.

Discovering DNA

One of the more remarkable things about On the Origin of Species is that Charles Darwin articulated his theory without knowing the exact mechanism by which variation occurs. It wouldn’t be until Watson and Crick’s discovery of DNA in the 1950s that evolutionary biologists would finally have the answer.

(Credit: Pixbay/Public Domain CC0)

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The advent of genetics is the single most important thing to happen to the study of evolutionary biology since Darwin’s theory first appeared (with a respectful tip of the hat to Gregor Mendel and his discovery of the fundamental laws of inheritance). Because DNA is universal to all life, its presence strongly suggests that all creatures on Earth evolved from a common ancestor.

It also explains how the proliferation of genetic mutations (essentially copy errors), combined with the processes of natural selection, enables evolution to happen. Ultimately, DNA is the engine that drives evolution. It’s an elegant—sometimes brutal—process that doesn’t require a guiding hand. Natural selection is a wholly autonomous process, thus earning it the moniker of “God killer.”

Finding Transitional Fossils

Species come and go, but life goes on. This is the essential lesson of the extensive fossil record—one that dates back 3.8 billion years. What’s more, it’s a chain of continuity used by evolutionary biologists to study the various interconnected progressions made by species as they change over time. So-called “transitional fossils” — like the recent discovery of Pappochelys, a 240-million-year-old reptile with a set of emerging turtle-like features — provide evidence for “missing links” between two different species by showing some of the traits of both, although this isn’t necessarily evidence of direct descent. Biologists use each discovery of such new species to fill in the evolutionary gaps.

The recent discovery of Pappochelys, a 240-million-year-old reptile with a set of emerging turtle-like features, is helping scientists fill in an important evolutionary gap—while causing great consternation to creationists. (Credit: Rainer Schoch/Nature)

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The presence of so many fossils demonstrates the ever-changing diversity of life since it first emerged. From life’s early beginnings as single-celled prokaryotic cells through to the Cambrian Explosion and the emergence of dinosaurs and mammals, it’s a story of continuous adaptation. Creationists like to believe that certain evolutionary steps are intractable, but as more and more transitional fossils are discovered, it’s clear that each evolutionary advance can be explained.

For example, some creationists argue that evolutionists cannot identify missing links between reptiles and birds. A post from Scientific American offers a compelling rebuttal:

Actually, paleontologists know of many detailed examples of fossils intermediate in form between various taxonomic groups. One of the most famous fossils of all time is Archaeopteryx, which combines feathers and skeletal structures peculiar to birds with features of dinosaurs. A flock’s worth of other feathered fossil species, some more avian and some less, has also been found. A sequence of fossils spans the evolution of modern horses from the tiny Eohippus. Whales had four-legged ancestors that walked on land, and creatures known as Ambulocetus and Rodhocetus helped to make that transition. Fossil seashells trace the evolution of various mollusks through millions of years. Perhaps 20 or more hominids (not all of them our ancestors) fill the gap between Lucy the australopithecine and modern humans.

Indeed, fortuitous mutations have fueled a trial-and-error process that have produced gradual but dramatic changes in species over the course of eons. Some evolutionary offshoots worked for a while, but changing circumstances—such as difficult environmental conditions or the introduction of a rival species—produced dead ends (e.g. wooly mammoths, sabre toothed tigers, and very likely, the panda bear). Other branches proved more resilient, allowing species to continue in novel directions (birds, as an offshoot of dinosaurs, are an excellent example). And yet some species, such as cyanobacteria, coelacanths, and crocodiles, have barely changed, showing that evolution doesn’t fix what ain’t broke.

Archaeornithura meemannae is the oldest known relative of modern birds (Credit: Wang et al/Nature)

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Fossil discoveries also show the interconnectedness of species over time. A great example is the recent discovery of Archaeornithura meemannae, a newly discovered species that is now the oldest-known member of an evolutionary branch that includes all living birds. This creature fills an important gap that explains its presence among other contemporaneous birds, while also pointing to other yet-to-be-found bird-like creatures. These transitional fossils allow paleontologists and cladisticians to iteratively piece together the great chain of being.

Matching Traits to Common Ancestors

Typically, evolutionary biologists like to point out the differences in species as they branch away from common ancestors, but they also like to identify those characteristics that remain common to both. This serves the dual purpose of showing evolution-in-action, while also demonstrating the subtle ways in which speciation can occur.

A simplified diagram showing the evolution of the horse. Each name represents a group of related species. As this chart shows, evolution rarely follows a straight line, but instead branches in many directions. (Credit: Humboldt)

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For example, the form and structure (morphologies) of deer, moose, horses, and zebras are strikingly similar. Not surprisingly, they share a common ancestor. Similarly, seagulls and pelicans are similar in their appearance, behavior, and DNA. Again, they share a common ancestor, from which they deviated in relatively minor but important ways. Similarly, Homo sapiens and Homo neanderthalensis were more alike than they were different, branching off from the evolutionary tree fairly recently in evolutionary history.

As Darwin pointed out 150 years ago, these common characteristics provide indisputable data points in favor of evolution, showing the ways in which species diverge when circumstances change.

Identifying Vestigial Traits

One of the more compelling arguments in favor of evolution is the presence of vestigial traits—physical characteristics that are gradually working their way out of an organism’s genetic profile. Most of these traits are benign, but some can be harmful (which is why they’re often referred to as “evolutionary baggage”).

You can blame your ancestors for your impacted wisdom teeth. (Credit: Coronation Dental Specialty Group, CC-BY SA 3.0)

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Just as full-blown characteristics don’t appear overnight—such as flight in birds, or an elephant’s long and dextrous trunk—traits that are no longer required for an organism’s day-to-day survival take a long time to disappear. These characteristics fade away because there’s no pressure for the gene or genes in question to retain them, resulting in faded or lingering traits that bear a weak resemblance to their original form.

In humans, classic examples include the appendix, wisdom teeth, the coccyx (or tailbone), and tonsils. Certain behaviors can also be considered vestigial, such as the Palmar Grasp Reflex and our instinctive aversions to bugs and snakes.

Identifying Imperfect Characteristics

Because our current physiological form is derived from those of our ancestors, we can hardly be considered an ideal species; there are many inherent design flaws in the human body. The throat (pharynx), for instance, serves as a conduit for both food and air. In males, the urethra both helps move urine from the bladder and transports sperm to the penis. Then there is our inability to biosynthesize vitamin C, the extremely narrow birth canal (in women), and our over-loaded lower backs.

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(Image at left: This is where it hurts: So much pressure on the lumbar vertebrae (Photo credit: Patrick87/CC BY-SA 3.0)

Unlike deliberate conscious design, evolution doesn’t care about perfection. Adaptations simply need to be good enough. What’s more, evolution cannot start from scratch; each species has to be crafted from its previous form, which can often lead to awkward or problematic characteristics.

Studying Early Embryo Development

Embryos of humans and other animals often bear similar physical characteristics at certain stages. This is because they share ancient genes.

(Credit: Stihili/Shutterstock)

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Discovery News explains:

These ancient genes are expressed during a middle “phylotypic period” of embryonic development for all species. Developing human, fish and other embryos therefore at times share features, such as tails and gill-like structures.

Human embryos resemble those of many other species because all animals carry very ancient genes. These genes date back to the origin of cells, which are expressed during a middle phase of embryonic development, according to two separate papers published in this week’s Nature.

The findings help to explain why our embryos have a tail when they are a few weeks old and why human embryos retain other characteristics, such as fur-like hair and fish embryo similarities, seen in the developmental stages of other species.

Typically, the similarities are more pronounced for more closely related species.

Observing Evolution Over Short Timescales

It’s a myth that evolution requires timescales that are too long to be observed by humans. In many instances, environmental changes occur so suddenly that certain species are forced to adapt quickly to the changing conditions.

The color black: a simple but fortuitous adaptation for a moth in a polluted environment. (Credit: umn.edu/Kettlewell)

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A classic example is the peppered moth, an organism that evolved a particular color variation as a consequence of the Industrial Revolution. Prior to this period, these moths regularly appeared in versions of black and white. But owing to sooty pollution from factories, the white moths had a hard time blending in. The result was an increase in black moths and a dramatic decrease in white moths. University of Wisconsin geneticist Sewall Wright referred to it as “the clearest case in which a conspicuous evolutionary process has actually been observed.”

But there are other examples worth pointing out. Our war against bacteria is rapidly producing highly resistant strains, leading to fears of a post-antibiotic era. Similarly, many animals are adapting to pesticides, including fruit flies and even rats. In one striking example, the Colorado potato beetle has evolved to resist 52 different compounds belonging to all major insecticide classes.

Simulating Evolution on Computers

Another way to witness evolution is to simulate it. Evolutionary biologists have been doing this for years, using computers to create virtual populations subjected to all sorts of environmental pressures. The beauty of these simulations, aside from demonstrating that natural selection actually works, is that scientists can run their simulations at high speeds to observe sweeping changes over long timescales. What’s more, they can run the same simulation thousands of times to produce consistent, measureable results.

Spore video game.

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For example, evolutionary biologists have used computer simulations to show that humans worked together to evolve bigger brains, and that the onset of grandmothers may have contributed to lengthy human lifespans. Simulations have also shown that mass extinctions can accelerate evolution, and that limited lifespans are an evolutionary adaptation.

Scientists are also using the powers of evolution to develop medicines and robots (both virtual and real). Recently, researchers from the University of Cambridge created a robotic system that can build its own “children” and then decide which version performs best to inform the design of the next generation.


Email the author at george@io9.com and follow him at @dvorsky. Top image: An artist’s impression of the mouse-sized Xianshou Songae, a tree-dweller in Jurassic forests. Illustration by Zhao Chuang.