It is actually extremely rare for the bones of a living creature to become fossilized. The remains of an organism need to be covered by sediment as soon as possible after death, or come to rest in an oxygen-free environment such as the bottom of a lake or frozen in ice. Despite the odds, the fossil record uncovered so far is overwhelmingly abundant. In it contains clear examples of intermediary species, along with the answers to how modern life came to be.
Whales and dolphins resemble fish but are obviously mammals. They have hair, give live birth, feed milk to their young, are warm-blooded, have lungs, and don’t have gills. They also move by undulating up and down like how otters swim or dogs run, instead of side to side like fish. Their skeletons show even more mammalian traits. Their flippers consist of arm, wrist, hand, and finger bones. They even have fundamental hip, thigh, and shin bones.
Why would animals without hind legs, have hind leg bones? Why do their flippers have the skeletal structure of mammalian arms or forelegs? The fossil record shows us the answers from Pakicetus to Ambulocetus, Dalanistes, Rodhocetus, Takracetus, Gaviocetus, Dorudon, Basilosaurus, and up to modern whales. The fossil record shows the transition from four-legged mammals that lived in shallow waters to whales and dolphins. In the transition, we see the introduction of new traits like shorter hind legs, more powerful tails, and tail flukes.
Most mammals breathe through a nasal opening located near the tip of their snout, but dolphins and whales breathe through a nasal opening on the top of their head. If these sea mammals evolved from land mammals we should see, in the fossil record, the transition of the nasal opening migrating to the top of the skull. And that is exactly what we see!
Basilosaurid whales lived about 34 to 40 million years ago, and are known for having multiple well-preserved fossils. Located halfway up their snout is that nasal opening the theory of evolution predicted.
Homologous structures are structures that are similar in different species, even if the body part serves different functions. The humerus, radius, ulna, carpal, and finger bones of our arms are also found in whale flippers, bat and bird wings, and the legs of cats. Since evolution works by altering existing parts for new uses, homologous structures are only found between species that share a common ancestor that also had the same structure. They show us the common ancestry of species, the more closely organisms are related the more similar their homologous structures are.
The inner ear structure of all modern mammals consists of 3 bones: the malleus, incus, and stapes. The ears of reptiles however only have the stapes bone, while the malleus and incus bones are part of their jaws. In the fossils of synapsids (mammal-like reptiles) we see these bones transitioning from the jaw to the ear. You may wonder, why are ear bones in the jaw of reptiles? Reptiles actually use their jaws to help them hear. While resting on the ground, their jaws transmit vibrations to their inner ear.
Several species of fish alive today can walk, like the Spotted Handfish and the amphibious fish known as mudskippers. 375 million years ago there existed Tiktaalik, the fish ancestor to reptiles. Tiktaalik is technically a fish, complete with scales and gills, but it had the sturdy wrist bones, neck, shoulders, and thick ribs of a four-legged vertebrate. Tiktaalik was specialized for life in shallow water, propping itself up on the bottom and snapping up prey. Its well-preserved fossils were discovered in 2006 and were also easy to find. Paleontologists already knew approximately when and where fish first transitioned to land. They just needed to look at 375 million-year-old rocks that were preserved in a Canadian river delta.
Where fossils and living species are found paints an even clearer evolutionary history of life. As evolution predicted, the closer species are related, the closer they are also found geographically. Species are also not found on land masses that their ancestral species did not have access to. They are geographically distributed based on their evolutionary history, and not simply distributed wherever the climate and environment provide a suitable habitat.
South American animals are perfectly suited for living in Africa, and vice versa, but you won’t find any of them residing in the other continent naturally. Hawaii serves as a very hospitable environment for many mammals. Pigs and goats multiplied there after being released as wild animals. Despite this, they and all other large mammals on the Hawaiian islands were brought there by man, none of them are native to the islands. It doesn’t matter how hospitable an environment is, species only exist and evolve in the geographic areas that were colonized by their ancestors.
Protylopus are the extinct ancestors to modern camels. They did not have humps, were much smaller, and lived in North America during the Eocene Epoch. By examining where fossils are found we can trace their journey across the Bering Strait to Asia, and eventually Africa. There they evolved into the Bactrian camels we know today in eastern Asia and the dromedary camels in Africa. The fossil record also shows that some Protylopus headed south, across the Isthmus of Panama. There they evolved into the modern day llamas and alpacas in South America.
Vestigial structures are compromised versions of structures, usually organs, that appear fully functional in evolutionary ancestors but lost most, if not all, of their original function. Evolution works with tinkering existing features instead of working from scratch, and these compromised structures clearly show transitions from one species to another. In some cases, these vestigial structures are downright harmful and deadly.
In plant-eating vertebrates, the appendix is much larger and helps with digesting their largely herbivorous diet. The appendix in humans is a small pouch attached to the large intestine. It does not directly assist with digestion and humans simply do not have any need for it. In fact, in the United States during the year 2000, nearly 300,000 people had their appendix removed. Why do you ask? Because this unnecessary organ can be deadly for humans, due to a condition known as appendicitis. That same year, the human appendix has caused 371 deaths in the United States alone.
The appendix isn’t the only vestigial structure that humans need to have removed. Most people also get their wisdom teeth removed. The jaw in humans is small than that of our evolutionary ancestors, so much so that it no longer has enough room for all our teeth. Because of this, when our wisdom teeth grow in they need to cram their way into an already full collection of teeth. The result is them growing in at various angles, pressing up against our other teeth, which leads to various dental issues including serious pain.
The cave-dwelling tetra fish known as Astyanax Mexicanus have small vestigial eyes. They do actually form regular eyes during their development, but while still in the egg, their eyes begin to degenerate during the later stages of development. In addition to that, their eyes are even permanent covered by a slap of skin. The end result is nonfunctional eyes and in blind fish.
It is believed that the genetic mutations that degenerated their eyes may have also increased their number of taste buds. After all, evolution is commonly about trade-offs, and in dark caves taste is more useful than vision.
Some may argue that vestigial structures are evidence of creation, claiming that since animals are created with similar tool kits there must have been a conscious creator. In reality, they actually show the sort of limitations you would expect to see if there wasn’t a conscious creator. Just like homologous structures, vestigial structures are only found between species that share a common evolutionary ancestor that also had the same structure. They are also inefficient structures that cause far more harm than good, making them clear examples of “unintelligent design.” The sloppy design of many organisms can only be explained by evolution’s tinkering.
Where and when species appear in the geological record perfectly matches up with what we would expect to see if evolution were true. Invertebrates appear before vertebrates, fish before frogs, and reptiles before mammals. We never see human fossils mixed with Trilobite fossils or squirrel fossils mixed with dinosaur fossils.
In many cases, the evolutionary history of any individual organism unfolds during its development. You can clearly watch an embryo exhibiting characteristics of the embryos of its ancestors. One can often observe a structure appearing at one stage during embryonic development that corresponds to an ancestral structure which is no longer present in a species, only to disappear or become altered in a later stage of development. These relict developmental forms clearly show that our development has evolved, with new instructions layered on top of old ones.
Chickens do not have teeth, but their ancestors did. Chicken still have the ancestral genes to grow teeth, but they also have a newer gene to get rid of their teeth. That is how evolution works, not by removing old instructions, but by adding new instructions. These instructions in an organism’s DNA play out during its development. Because of this, the embryos of chicken can be seen growing teeth before the newer gene kicks in to remove the teeth. If scientists remove that later gene, or if that gene simply fails on its own, then you will have a chicken born with a full set of teeth.
Chicken also have the genes to grow tails, and so do humans. We, like chicken, evolved from ancestors who had tails. Because of this, we still have the genes for grown tails. During the early stages of a human (and chicken) embryo’s development, you can see a tail developing. It is not until later that a newer gene kicks in and unleash white blood cells to dissolve the tail. However, sometimes that later gene fails and a human is born with a tail. Some are just stubs or flaps of skin where a tail should be. Other times a human baby is born with a 13 centimeters long tail that consists of skin, fat, connective tissues, nerves, and muscle tissue. Because they have muscle tissue inside, the tails can be moved back and forth or even contracted into curves.
If evolution is true, and all organisms share a common ancestry as predicted, then we should be able to see traces of this in our DNA. This is exactly what we see. Since our DNA has been handed down from every evolutionary ancestor our genome carries a lot of evolutionary baggage. Comparing that baggage between species allows scientists to determine how closely related one organism is to another.
Phylogenetic, or evolutionary, trees are commonly based on a comparison of physical or behavioral features, but with DNA sequencing we can construct a tree based on the comparison of genes or proteins. After a genome is mapped, its sequence can be compared to other genomes with computer programs and statistical algorithms. With more precision than ever, we can see how closely related species are based on how closely their genome matches up. The genome of humans varies by only 0.1% from other humans. And as expected, there is only a 4% difference between the genome of humans and chimpanzees. The genetic difference between humans & cats is 90%, humans & mice is 85%, humans & cows is 80%, and humans & chicken is 60%.
Evolution tells us that we share a common ancestor with the great apes: chimpanzees, gorillas, and orangutans. If this is true, then why do we only have 23 chromosome pairs while great apes have 24? While this genetic difference may seem like an issue, a closer look at our gnome tells us that a chromosome did not go missing, it simply fused together with another. Chromosomes have markers, at each end are telomeres, and in the middle is a centromere. Our chromosome 2 has two centromeres and 4 telomeres, two of which are connected in the middle. This clearly shows us that two chromosomes fused together, but more importantly, it is the combination of chromosomes 2a and 2b found in great apes.
Less than 10% of human DNA has a functional role, the rest is biological baggage that has built up over our evolutionary history. By comparing the genome of various mammals, scientists at Oxford have narrowed down what genes were potentially important enough to be conserved across species. And while over 90% of our DNA is proven not needed by evolution, additional research shows that only 1% of our DNA is used for the development of the crucial proteins need for our development, health, and to keep us alive. All of this genetic baggage can only be explained through evolution. It also sheds new light on why well over half the cells in our bodies are not human cells, but rather cells to produce microbes and bacteria that live off of us.
What makes all the evidence for evolution really powerful is that it all matches up! Transitional fossils are found in rocks of just the right age and in just the right location, matching up with both the evolutionary timeline and the ancestral migration path of species. Fossils are not randomly scattered and their structures show us an evolutionary “family tree” branching out from a common ancestor. The discoveries in genetics and DNA also show us an evolutionary family tree, one that matches up exactly with the fossil record. The evidence found in embryos and vestigial organs both illustrate this same family tree. Dating/age, migration paths, the fossil record, embryos, vestigial organs, genetics, and DNA all independently tell the exact same story. Exactly as the Theory of Evolution predicted!
The abundant evidence from various fields of science tells us that all life is connected. A connection that can be traced through each species, back to a single common point of ancestry. While some may argue that similarities are evidence for a conscious creator, one who builds from a common tool kit, the evidence argues differently. It shows us limitations, the DNA and thus physical structures that an animal is comprised of are limited to that of what it’s evolutionary ancestor had. Where species are found geographically is limited to where their evolutionary ancestors had access to. These limitations have also lead to extra baggage, leftover parts, and design flaws leading to what has become known as “unintelligent design.” The beauty, diversity, and sloppiness of life can only be explained through evolution.