During my summer holidays, I used to work as a part-time teacher at a student care for primary school students aged 7-12 years old. When reading time came, they would huddle around me while I read and explained to them scientific concepts from the Young Scientist Series. The most frequent question was "Teacher Keane! Where did we come from? Who made us?" To which, I responded by explaining to them in simple terms, with reference to the Young Scientist magazines, how evolution gave rise to all plants, fungi, insects, and animals, including humans. Most of their eyes glimmered with excitement as they learned about fun evolution facts, such as the stupendously old age of the Earth, or that whales used to walk on land, or that their 185th millionth grandfather was a fish. Though only the older students could grasp the last one... These same excited children then turned to the main teacher of the student care to share what they've learned from me. To which, the teacher responded, "Utter rubbish! God made us!" Now, I will not dispute the claim of a God because it is an unfalsifiable claim, and religion deals with non-science topics such as ethics, spirituality, and the arts, not about the natural physical world. Furthermore, I also acknowledge and respect that everyone has the right to have such personal beliefs. However, where I draw the line is when such personal beliefs enter the classroom and impede the science education of future generations.
Recognising evolution is crucial for advancing biological science and holds broad implications for daily life. However, a significant portion of the public, just like the teacher I've mentioned, currently rejects biological evolution. Despite the overwhelming evidence in favour of evolution accumulated throughout the past 150 years, the prevalence of evolution-denial among the general public is still rather widespread across various countries. A study conducted by Pew Research Center (2020), surveying the population of 20 countries from Europe, Russia, Americas, and Asian-Pacific, revealed that a median of 74% accept that humans and other living things have evolved, while a median of just 21% disagree and think that humans and other lifeforms have always existed in their current forms. Although this shows that majority of people across these regions accept evolution, Singapore surprisingly ranks 17th out of the 20 countries, with 59% of its population accepting evolution. This is despite having one of the most highly educated population in the world. Only India, Brazil, and Malaysia had lower prevalence of evolution-acceptance. The study also found that denial of evolution is strongly linked with religiosity, possibly because certain creation myths are interpreted as literal instead of figurative. Interestingly, the infamous Tennessee Anti-Evolution Act, which was enacted on March 13, 1925, was a state law that once made it illegal to teach any theory that denied the divine creation of humans. Of course, the act is now nullified, as it ought to be. Back to the acceptance of evolution, in contrast with the general public, nearly all scientists (97%) from the American Association for the Advancement of Science (AAAS) accepts biological evolution as a fact (Pew Research Center, 2009). This highlights a stark difference between the public and scientific consensus on evolution.
Biological evolution by natural selection is a product of rigorous scientific inquiry into the natural world, and it serves as a foundational principle linking various biological disciplines like genetics, biochemistry, neurobiology, physiology, and ecology. Additionally, evolution helps to explain the development of organisms on Earth, including humans, and sheds light on numerous aspects such as the origin of infectious diseases, antibiotic resistance in bacteria, agricultural dynamics between wild and domestic species, Earth's atmospheric composition, and cellular processes. Therefore, I find it to be essential for people in the 21st century to understand and scrutinise the evidence for evolution and come to the only logical conclusion. That is, evolution is a fact just like how germ theory and atomic theory are both facts. Click here to read about the mechanism of evolution by natural selection. Click here to read about the mechanism of evolution by natural selection.
"Nothing in biology makes sense except in the light of evolution." - Theodosius Dobzhansky (1973)
Evolution-denialists commonly cite creationism to be the explanation of all life on earth, claiming that a creator designed the complex bodies of organisms. Yet even till today, no robust evidence (i.e., falsifiable, empirical, reproducible, public) lends credence to such claims. This blogpost is to display the vast array of robust empirical evidence from various scientific disciplines that support biological evolution by natural selection, and to hopefully, convince evolution-denialists to align their views to where the evidence points. Additionally, it's also meant to demonstrate the beauty and wonder of how science gathers and scrutinise evidence, helping humanity to understand the very mechanism that gave rise to the bountiful diversity of life on Earth!
This image is created with the assistance of DALL·E 3
Radiometric Dating
Before we touch on the evidence, we will go through the method called radiometric dating. Radiometric dating is a method that relies on the fundamental principle that radioactive isotopes within geological materials undergo consistent and known rates of decay, resulting in the formation of daughter isotopes (Britannica, 2021). Through analysis, natural radioactive elements in rocks and minerals allows scientists to gauge the age of rocks, fossils, and wooden aretfacts.
For instance, Uranium-238 (U-238) decays into lead-206 (Pb-206) through a process, and using this process to date rocks is known as uranium-lead dating. The half-life of uranium-238 is approximately 4.5 billion years. This means that after 4.5 billion years, half of the uranium-238 in a rock will have decayed into lead-206. Uranium-238 dating is commonly used to determine the age of Earth's oldest rocks and minerals, providing a valuable tool for understanding the deep geological history of our planet. Another example would be potassium-argon dating, whereby potassium-40 (K-40) decays into argon-40 (Ar-40), with a half life of potassium-40 being approximately 1.25 billion years.
Half-lives of isotopes are constant and therefore, are able to be calculated in labs. Note that uranium-lead dating and potassium-argon dating are just two pairs of radiometric dating methods. Scientists have used numerous other pairs of isotopes for dating. What is the outcome of using various pairs of isotopes which all have differing half-lives? The answer is that all measurements point toward 4.5 billion years for the oldest rocks on Earth, the moon, and asteroids. Therefore, we know the age of earth and our solar system to be 4.5 billion years old. In summary, Radiometric dating is a reliable and tested method that allows us to date the age of rocks and fossils precisely with an extremely low margin of error, since the early 20th century (Boltwood, 1907), via the analysis of the isotope contents within a rock or fossil. To date the age of fossils, scientists employ carbon dating on the fossils themselves or they use various radiometric dating methods, such as uranium-lead dating, to date rocks that are found in the same rock layers as the fossils. This gives us the age of the fossils, using the date of the rocks as a proxy.
After one half-life has passed, 50% of the parent isotope would decay into the daughter isotope. After two half-lives have passed, 25%; after 3 half-lives, 12.5%; and it goes on and on and the method becomes less accurate as time passes. However, since we have isotopes like uranium-238 that have half-lives of 4.5 billion years, we are able to date rocks that are billions of years old.
There's one creationist website (there are many) that I came across, titled answersingenesis.org, that attempts to debunk radiometric dating citing that scientists are not sure whether the chemicals can be contaminated by outside forces. This shows a lack of understanding of how radiometric dating works, because such contamination can be prevented by for example, dating igneous rocks. These are rocks which are formed by solidified magma and lava. This process of solidification locks in the isotopes, preventing contamination and thus, forming a reliable molecular clock. To drive the point once more, radiometric dating is accepted as an exceptionally accurate dating method, garnering overwhelming consensus amongst the scientific community.
Fossil Record
Let' start with the first major line of evidence for evolution... Fossils! Fossils are the remnants of once-living organisms, which are formed in such sedimentary rock layers. That's how we know dinosaurs existed. I sincerely hope that none of my readers are dinosaur-denialists...
Everywhere in the world, the fossil record shows that in the lower rock layers (older), dated to be around 540 million years ago, there only exist fossils of simple worm-like organisms such as Pikaia, which are the first chordates—animals with a basic backbone-like structure. No fishes, no amphibians, no reptiles, and no mammals are found in this old rock layers. As you move up to the higher rock layers (younger rocks), you'll start to see a progression of life forms evolving to become more complex. Gradually, fossils of jawless fishes start to appear, followed by jawed fishes, then amphibians, then reptiles, then birds and mammals, then primates, and then humans. Modern humans—Homo sapiens—only appear above rock layers that are dated to be younger than around 300,000 years, having evolved from ape-like ancestors in Africa.
Below is an image to illustrate. As mentioned, rocks are dated using several isotopes pairs of radiometric dating. Once again, note that no amphibian, reptile, or mammal fossil was ever found in the cambrian rock layer. In other words, classes of species appeared in the fossil record, in exactly that aforementioned order. The only logical conclusion is that mammals evolved from reptile-like ancestors, which evolved from amphibian-like ancestors, which evolved from fish-like ancestors, which evolved from worm-like ancestors, which then evolved from cells like Eukaryotes.
To falsify evolution, one simply has to find a mammal fossil in the cambrian rock layer, and evolution will go right out the window. Hmmmm... I wonder why evolution-denialists have not found any of such occurrence yet? It would be the easiest way to falsify evolution. Yet till today, no such observation has ever been made. Yes, you can search up online and find a bunch of creationist websites claiming they have such evidence as they attempt to deceive its readers from the fact of the matter. But none of such evidence are ever published in credible scientific journals. These creationist websites are biased in promoting creationism, aiming to distort the scientific facts that are empirical, reproducible, and public. In Singapore, students are taught in secondary schools and universities to verify the credibility of the sources. If I may suggest, you might want to check out the papers published from universities like Oxford, Cambridge, Harvard, MIT, Stanford, or scientific journals such as Nature or Science. These credible institutions are the engines of knowledge production and it would be wise to read their academic papers instead. Because if such creationist websites are trustworthy, then the Earth must be flat as well since there are countless flat-earth websites on the web.
Source: Encyclopædia Britannica (n.d.). Major Evolutionary Events [Image]. Encyclopædia Britannica. URL: https://www.britannica.com/science/fossil-record#/media/1/214564/1650
However, the fossil record is just one line of evidence.... Let's continue 'digging'!
Transitional Fossils
If evolution were true, we would expect to find intermediary species between two adjacent classes of species. For instance, between Reptilia and Aves (Birds) or Fish and Amphibia. In other words, if amphibians evolved from fishes via biological evolution by natural selection, we should find fossils that have amphibian-like and reptilian-like features, because a fish doesn't give birth magically to an amphibian. Evolution occurs gradually over millions of years, with small changes in each generation.
Meet Tiktaalik! It is one such intermediary species between fish and amphibian, exhibiting limbs with wrist bones, fish-like gills, and lung-like structures, with eyes on the top not on the sides. Looking at its reconstructed image below, based on fossils found of course, you wouldn't be able to tell if that was an amphibian or a fish.
Source: Zina Deretsky, National Science Foundation
Delving deeper into the evolutionary tapestry, Archaeopteryx emerges as a captivating transitional fossil, serving as a pivotal link between reptiles and birds (all birds today are reptiles). This remarkable specimen showcases an intriguing amalgamation of avian and reptilian features, encompassing feathered wings and distinct reptilian characteristics such as teeth, a long bony tail, clawed fingers on its wings, and the capacity for flight. If you didn't know, not all dinosaurs went extinct 66 million years ago. All living birds today ARE literally dinosaurs! Archaeopteryx is commonly regarded as the first "bird". It is in quotation marks because all birds today are also considered reptiles, in case you didn't know already. Essentially, birds are a subgroup of reptiles.
Source: Encyclopædia Britannica. (n.d.). Archaeopteryx. Retrieved January 4, 2024, from https://www.britannica.com/animal/Archaeopteryx#/media/1/32599/62467
It might sound wild, but whales actually trace their roots back to a four-legged land mammal from about 60 million years ago. That's the reason why your elementary or primary school teacher taught you they're mammals, covered with tiny hairs, nurse their young with milk, and breathe through lungs instead of gills. Numerous discoveries of transitional fossils walk us through the evolution of their noses - a journey from the tip of their snout to the top of their heads, eventually morphing into the blowholes we know today. The transitional fossils also show how whales slowly lost their legs. Take a look at Rodhocetus. It's a remarkable intermediary species between the ancient 4-legged Indohyus and modern cetaceans. Evolution, it turns out, has numerous insightful and wonderful stories to tell, and the evolution of cetaceans is one of them.
Source: Whale phylogeny from The Tangled Bank, used with permission of the author, Carl Zimmer, and publisher, Roberts & Company, Greenwood Village, Colorado. Taken from: https://evolution.berkeley.edu/what-are-evograms/the-evolution-of-whales/
Source: Cold Spring Harbor Laboratory Press
Horses trace their evolutionary lineage to a five-toed ancestor, and the discovery of numerous transitional fossils documents the process by which they gradually evolved from having five digits to three, eventually culminating in the singular middle digit that constitutes the hoof observed in contemporary horses.
Source: (Solounias et al., 2018)
Source: (Solounias et al., 2018)
Transitional fossils also provide evidence of the evolutionary progression in which the skulls of ape-like creatures underwent a transformation, characterised by an increase in size and a gradual reduction in the protrusion of their jaws. This process ultimately led to the emergence of the anatomical features observed in modern humans today. This, once again, is a remarkable story of how humans evolved from ape-like ancestors in Africa, a story that took millions of years to unfold.
Source: Encyclopædia Britannica. (n.d.). Human evolutionary pathways [Image]. Encyclopædia Britannica. https://www.britannica.com/topic/Homo-sapiens#/media/1/1350865/45440 Accessed January 7, 2023.
Comparative Anatomy
Moving on from the fossil record, the next line of evidence is comparative anatomy. If evolution were true, which claims that all reptiles (including birds) and all mammals evolved from a common amphibian-like ancestor, we would be able to see similarities in their anatomical structures. The homologies of the forelimb in six very different kinds of modern vertebrates are shown below. Interestingly, the flipper of a dolphin has 5 fingers, and this is because, as mentioned before, cetaceans like whales and dolphins evolved from a land 4-legged mammal. The bones in the wings of bats corresponds with a human's arm, bone for bone. This is because they evolved from a a small, quadrupedal, insect-eating mammal with pawed limbs (Gunnell and Simmons, 2005), and both bats and humans share a common ancestor. Despite the limbs of all these vertebrates serving very different functions, and appearing distinct from the external view, the analysis of their bone structures supports the fact that they all descended from a common ancestor. These observations, once again, only make sense from the evolutionary perspective.
Notes. Homologies of the forelimb among vertebrates, giving evidence for evolution. The bones correspond, although they are adapted to the specific mode of life of the animal.
Source: Encyclopædia Britannica. (n.d.). Homologies of Vertebrate Forelimbs. Retrieved January 7, 2024, from https://www.britannica.com/science/comparative-anatomy#/media/1/129617/45466
Another example of homology is the jaws and ears of mammals and reptiles. All mammals have one bone in their jaws and three bones in their ears. Lizards have several bones in their jaws and only one in their ears. In the field of embryology, it is found that during the gestation of a mammalian foetus, two skull bones transform into ear bones. In contrast, when a lizard undergoes embryonic development within its egg, those same two bones contribute to the formation of their jaw. These homologous observations support the fact that mammals evolved from reptilian-like ancestors.
Vestigial Structures
Have you ever wondered why do you have a tailbone, or wisdom teeth? Think about why would humans have an appendix that is no longer in use, but only causes problems such as infections, leading to arduous surgeries? Why on earth does a modern whale have leg bones in its body if it doesn't even have legs?! Why do snakes, which slither on the ground, have pelvic spurs protruding at areas where legs would have been. Why the heck do BLIND mole-rats have eyes??? The only logical explanation is that they all evolved. These defunct structures are known as vestigial structures, and they are features that a species inherit from an ancestor, but which no longer serve any major purpose.
The tailbone (coccyx) is a remnant of the tail, which the monkey-like ancestor of all modern apes (including humans) possessed. The wisdom teeth are the remnants of teeth which once fitted well in the larger jaws of our ape-like ancestors. Since then, our jaws have evolved to be smaller, allowing our skull and brains to expand in size. The appendix in the human body was once used to aid with digestion of tough herbivorous food, which constituted much of our ancestral apes' diet. The leg bones in whales today, as mentioned multiple times, are remnants inherited from their 4-legged ancestor which used to have legs. The pelvic spurs of snakes today are remnants inherited from their 4-legged lizard-like ancestor. The eyes of the ancestors of mole-rats were once capable of sight but have since lost its function as they gradually evolved and adapted to the darkness of the underground burrows. Their vestigial eyes are now covered with fur.
The only reason why any species should have vestigial strutures, is because they evolved. No designer or creator would build a blind mole-rat with eyes, or a leg-less whale with leg bones that do not even connect to its spine. No creator would design a human being with wisdom teeth that can't fit in their jaws, which frequently causes infection for some if not removed via oral surgery. However, these aforementioned vestigial structures make perfect sense from the evolutionary perspective.
For those living in Singapore, I invite you to take a trip to the Lee Kong Chian Natural History Museum (LKCNHM) at the National University of Singapore, and look for the whale skeleton exhibit. Have a look at the 5 fingers it possesses, as well as its vestigial leg bones. Oh.. and also have a look at their blowholes, there are 2 nasal passages not one, indicating that it's an evolved nose, as I've highlighted earlier. Below is a picture I took during my trip to the museum a year ago in 2022, but from this angle, you can only see the 5 fingers of the whale. For the vestigial leg bones and nasal passages, you'll have to visit the museum to see for yourself (I might snap another picture and upload it here in future). I highly recommend visiting the museum and I'm sure it will be an enriching experience for you! Bring your family and friends along and enjoy absorbing the magnificent diversity and story of life on Earth!
Source: Own Photo
Below shows the spinal structure of humans, take note of the tailbone (coccygeal vertebrae). It is a vestigial structure of the tails possessed by our monkey-like ancestor, such as Aegyptopithecus.
Below shows the image of the eyes of a Cape dune mole-rat (Bathyergus suillus). If you shave their fur, you can see their vestigial eyes. From this picture, you can see the shadows on the spots where the vestigial eyes are located at.
Source: (Nikitina & Kidson, 2014)
Below is an image of the vestigial leg structures of a Boa constrictor.
Source: Stefan3345, Taken from https://en.m.wikipedia.org/wiki/File:Rudimentary_hindlegs_spurs_in_Boa_constrictor_snake.jpg
Atavism
Best understood as a "reverse" vestigial structure, atavism refers to the condition whereby a genetic trait from ancestors resurfaces after undergoing loss in preceding generations due to evolutionary changes. Occasionally, a whale or dolphin will be birthed with tiny legs! Occasionally, horses are birthed with extra digits! Some humans are also born with miniature tails. The only reason why atavism would occur, is because living things evolved from ancestors who once had such structures, and a mutation causes such traits to arise once more in rare cases. Additionally, note that we do not see atavism whereby humans develop traits that were not present in our evolutionary ancestors. Atavism only occurs for traits that the species' ancestors possessed. For example, we do not see atavism whereby humans are born with wings or feathers because wings and feathers evolved in birds, after mammals have split off from their last common ancestor with birds around 310 million years ago.
Notes. Hind flippers present in a single anomalous dolphin housed at the Taiji Whale Museum
Source: (Thewissen et al., 2009)
Embryology
Embryology is the branch of biology that studies the development of embryos from the fertilization of an egg to the formation of a complete organism. Below is the embryo of a chicken and a human. The homologous gill slits and tails indicates a shared ancestry with fish-like ancestors. However, these gill slits do not form in the later stages of embryonic development for these 2 species. As for humans, the tails do not form fully, but they become the tailbone (coccyx).
Embryos of dolphins form hindlimbs but they slowly disappear as the embryo grow. These embryos are not drawn to scale. The first embryo is 6 mm, the last one 17.5 mm in length. Why would they develop hindlimbs in their embryonic stage, only for them to not grow into legs? The only logical conclusion is that they have a shared common ancestry with 4-legged animals, but have then since evolved to lose them as they adapted to living in the ocean.
Source: (Thewissen et el., 2009)
Biogeography
Biogeography, the study of organism distribution, explores how living beings are dispersed across regions. It delves into the interplay between Earth's physical environment and the evolutionary processes shaping species diversity and distribution. Consider oceanic islands, which provide a clear example of how geographical isolation impacts the evolution of species on isolated land masses.
Oceanic islands are young land masses that emerge from the ocean and are not part of any continental landmass. As such, oceanic islands like the Galapagos Islands contain mostly birds, many of which evolved to be flightless as there were no predators to escape from. Why are there no mammals on the island, except for seals and bats? It is because bats can fly and enter the island, and seals can swim and enter the island. Mammals such as lions and tigers are never found on oceanic islands and the reason being that they cannot fly across oceans. But if you ship a tiger or a lion to the island, they will be the apex predator of the Galapagos and they will thrive. In other words, they are fit to live on the islands and yet, they are not found on such islands. Why? The answer is because they evolved elsewhere and are unable to colonise the island due to the geographical barrier that is the ocean.
Furthermore, the study of biogeography shows that all the different species of birds in the Galapagos Islands evolved from birds living in the nearest mainland, specifically, the coast of Ecuador, which is the nearest land to the Galapagos, approximately 1,000 km away. The logical conclusion is that the ancestral species of birds migrated from the Ecuador coast and colonised the Galapagos.
These patterns are observed on other oceanic islands around the world such as the Hawaiian Islands and Madagascar. You can search up online scholarly sources for various other examples of evidence from biogeography which supports evolution.
Artificial Selection
Humans have bred dogs (Canis familiaris) from wolves (Canis lupus) and different vegetables from ancestral plants, by selecting specific traits. This process of artificial selection demonstrates that species evolve over time and in a short span of 40,000 years, you can get a chihuahua from a grey wolf. Evolution is the reason why you have cute little pet dogs, and delicious vegetables such as broccoli, corn (maize), kale, carrots, brussel sprouts, and numerous others. For greater explanation, please click here to read more on this in my other blog post titled What is Evolution by Natural Selection?
You might be wondering, does it mean humans knew about evolution 40,000 years ago? The answer is no. They knew they could breed for a certain trait in dogs or plants, but nobody understood the genetic mechanism of evolution, or even thought that the same mechanism used to breed them applied to ALL life on earth. The latter was the revolutionary discovery by both Darwin and Wallace, who arrived at the idea independently in the 1800s.
Below is an infographic showing how the ancestral Canis lupus was domesticated by humans, which gave rise to the hundreds of breeds of dogs that we know and cuddle today!
Source: This image is taken from http://www.dogica.com/dogevolution.html
Direct Observation and Experimentation
Because huge scientific and technological advancements have only come about in the past 200 years, it is impossible to directly observe huge evolutionary changes such as a mammal evolving to adapt to aquatic life in just 200 years because it took 50 million years for Pakicetus to evolve into modern whales. Even 10,000 years, the age of human civilisation, would not be enough to observe such macroevolution. But, as it should be obvious by now, macroevolution is well supported by various lines of evidence that have been presented in this blog. It is also rather simple to infer that small changes in a short period of time lead to huge changes in a long period of time. Nevertheless, we can directly observe microevolution in action today. Bacteria are evolving to becoming resistant to antibiotics. Insects are evolving to become pesticide resistant. Seals are slowly evolving to aquatic life. These occur in the wild, but what about in experiments?
My favourite example is the ingenious Siberian fox experiment conducted by Dmitry Belyaev in 1959. He carried out this experiment to study the process of domestication in real time. To achieve this, he selectively bred them for one particular trait, tameness. Whichever fox that is aggressive and fierce will be removed from the group. Only those which are obedient get to breed. In just six generations, the population of wild ferocious evolved to something completely different. They displayed behaviours such as licking hands, being receptive to be picked up and petted, whining upon human departure, and wagging their tails when humans approached. Their ears were no longer pointing upwards and instead, started becoming floppy. They also evolved to have more juvenilised facial characters, including a shorter, rounder snout, than wild foxes. Sounds familiar? That's because it is the same exact process in which dogs were domesticated across 40,000 years by humans, from the grey wolf. Many of these domesticated foxes ended up being adopted and I sometimes wished I could have been one of the adopters just because of how cute they would look as personal pets!
Mechta (Dream), the first of the domesticated foxes to have floppy ears 1969
Source: (Dugatkin, 2018)
The domesticated foxes have more juvenilized facial characters, including a shorter, rounder snout, than wild foxes
Source: (Dugatkin, 2018)
DNA Analysis (Molecular Biology)
When Charles Darwin released "On the Origin of Species" in 1859, the molecule governing the transmission of genetic traits from parent to child, known today as DNA (deoxyribonucleic acid), was unknown. The groundbreaking discovery of its double-helix structure by Crick and Watson in 1953 marked a pivotal moment in biology. Subsequent technological advancements have empowered us to map the genomes of numerous species, including our own, ushering in a new era of understanding the intricacies of genetic information and evolution. In fact, gene editing is no longer fiction, with the development of CRISPR-Cas9 in 2012, which led to the developers winning the 2020 Nobel Prize in Chemistry.
DNA comprise of 4 nitrogenous bases, namely, Adenine (A), Thymine (T), Cytosine (C), and Guanine (G). DNA code can be read exactly like letters on a book. A gene is made up of a specific sequence of DNA "letters". DNA analysis shows that species sharing a closer evolutionary heritage manifest a greater degree of genetic resemblance in their DNA sequences. Additionally, DNA analysis is also used to verify the link between modern organisms and transitional fossils.
Humans share the highest genetic similarity with chimpanzees with around 98% similarity. DNA analysis of whales' genetic code reveals that their closest ancestors are Hippopotamus. That's mind-blowing if I haven't told you that whales evolved from land mammals. This discovery was actually even shocking for biologists back then who knew that whales were once land mammals. But if you observe carefully, you will realise that whales and hippos share very unique similarities. They're both semi-aquatic, they nurse their young with milk underwater, they share similar dental and reproductive structures, and they exhibit similar social behaviours as well as underwater communication. DNA analysis show that hippos and whales descended from a common ancestor that lived around 60 million years ago.
DNA analysis is the single most powerful evidence for evolution, and if Darwin was alive today, he would've been pleased to have known that the discovery of DNA provided enormous support for his remarkable theory of evolution. So far, countless species have been mapped out on a phylogenetic tree based on DNA. The outcome reveals a compelling visual representation of the intricate interconnectedness of life, showcasing shared ancestry, and highlighting the diverse evolutionary pathways that have led to the rich tapestry of biological diversity we observe today. All life evolved from a single-celled common ancestor which lived around 4 billion years ago.
Conclusion
In this blogpost, I have presented numerous independent lines of evidence for evolution, encompassing radiometric dating, the fossil record, transitional fossils, comparative anatomy, vestigial structures, atavism, embryology, biogeography, artificial selection, direct observation and experimentation, and DNA analysis. As such, these different independent lines of evidence from various scientific disciplines all support the only logical conclusion. That is, evolution is the process in which how all life evolved from unicellular to multicellular organisms, across the span of approximately 4 billion years. As such, all living things are related and share a common ancestry. None of the evidence that I've presented have contradicted each other. In fact, they all corroborate each other to tell the same story. Evolution, just like any scientific theory, is easily falsifiable and yet, it has not been falsified. It is clear that the overwhelming evidence in support of evolution is undeniable to any rational, critical, honest, and unbiased mind, and I hope that with time and proper education, the acceptance of evolution can one day be universal, just like how almost everyone accepts the atomic theory, germ theory of diseases, and the heliocentric theory. To those who doubt it still, the world is eagerly waiting for you to falsify evolution, as that is precisely how science progresses; by proving itself to be wrong. Scientists rejoice when they are proven wrong! Anyone who can manage to successfully falsify evolution would undoubtedly and instantly win the Nobel prize. Until then, we shall stick with evolution, one of the strongest and revolutionary scientific theories there is, in the history of humankind. I'll end of with a quote by the esteemed evolutionary biologist Richard Dawkins, emeritus fellow of New College, Oxford, in the ending of his book titled "The Greatest Show on Earth: The Evidence for Evolution".
“Evolution is a fact. Beyond reasonable doubt, beyond serious doubt, beyond sane, informed, intelligent doubt, beyond doubt evolution is a fact...That didn't have to be true. It is not self-evidently, tautologically, obviously true, and there was a time when most people, even educated people, thought it wasn't. It didn't have to be true, but it is....Evolution is the only game in town, the greatest show on earth.” ― Richard Dawkins, The Greatest Show on Earth: The Evidence for Evolution
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