What you’re about to read is a paper I wrote as a part of my undergraduate coursework for Evolutionary Biology. I am sharing this here with a hope to enlighten you with some solid evidence for evolution. Enjoy.
The change of characteristics of a species over time is known as evolution. Both before Darwin and after Darwin, systematists have classified organisms by comparing characteristics among them. Darwin’s theory of descent with modification from common ancestors stated that species change over time and give rise to new species and share a common ancestor. Darwin’s finches are an example of Descent with Modification. This theory is applicable when one species gives rise to more than one species. Charles Darwin developed the hypotheses about natural selection. According to this theory, heritable traits help organisms survive and reproduce. The theory of natural selection was based on multiple factors- traits can be inherited and passed onto offspring, the fittest offspring survives due to environmental factors such as food and other resources, each offspring is different from the other. Evidence for evolution is extremely important for understanding the evolutionary history of organisms and their ancestry. All living things on earth are related and evolution is powered by natural processes.
The hypotheses of this paper is to study the evidence for evolution with an explanation and without any assumption.
With this, Darwin solidified the idea that species at different points in time share common ancestors. He called this the ‘tree of life’. But how do we know evolution occurred? For this, we need to look at the evidence for evolution.
Evidence for evolution is based on anatomical structures, the geography of species, fossils, molecular biology, and direct observation. Evolution occurs on small and large scales. Small scale (microevolution) affects only one or two genes and brings about very small or almost negligible changes in a species. Large scale (macroevolution) affects a whole population or species and may also form an entirely new species over a long period of time. Evidence for evolution can be studied over both small scale and big scale.
- Anatomical features
This can be understood based on the changes in physical features of a species that may have a common ancestor. Such anatomical features are known as homologous features. An example in plants could be the leaves of the pitcher plant, Venus flytrap, poinsettia, and cactus. Forelimbs of whales, humans, birds are also a great example of anatomical evidence for evolution.
Even though these look different on the outside, the inner structures of these bones are very similar on the inside. According to biologists, it is highly likely that whales, humans and birds had the same ancestor millions of years ago. Humans use their forearm to do work, we do not use to walk on them like dogs do. Birds use their forearms to fly and that same area in whales is the least grown, it uses it to swim. Another example of this would be forelimbs of moles, wings of bats, birds, pterosaurs. Modification of pre-existing structures explains why the stings of wasps and bees are modified ovipositors and why only females possess them.
Embryological similarities- In some cases, homologous structures are visible in the embryo, but they change while development. Homologous characters include some features that appear during development but would be unnecessary if the development of an organism were not a modification of its ancestors’ ontogeny. A good example of this would be branchial pouches in human embryos. These are like gill slits in fish embryos.
Vestigial structures- Darwin’s Descent with Modification helps us understand the presence of vestigial structures. Structures that are reduced in size and are not in use anymore are known as vestigial structures. These structures do not have their initial ancestral use. Examples of vestigial structures include flightless birds such as ostriches, emus, and penguins. These birds have wings, but they cannot flu. This is because they rose from a common ancestor that had wings. The appendix in humans is a vestigial structure. Whales and snakes have vestigial legs.
- Biogeography of species
Biogeography is the study of geographical distribution of organisms that provides information about how the species may have evolved. Biogeography tells us about niches. The geographic distributions of organisms provided both Darwin and Wallace with inspiration and with evidence that evolution had occurred. Darwin devoted two chapters of On the Origin of Species to showing that many biogeographic facts that make little sense under the hypothesis of special creation make a great deal of sense if a species – has a definite sense or region of origin, achieves a broader distribution by dispersal, becomes modified and gives rise to descendant species in the various regions in which it disperses. Darwin wanted to prove that species did not originate in one place, instead it had a common ancestor from where it had originated and moved from there.
Distribution in many taxa corresponds to geological events such as the formation and dissolution of connections between land masses. There are a lot of ecological factors that lead to biodiversity. The larger the habitat, the more available are the niches and less is the competition. Evidence of marsupial life was extracted from fossils in the Antarctic, South America and Australia. Marsupials did not migrate from one part of the world to another. The reason for the presence of this evidence would be the movement of tectonic plates over hundreds of years. Elephants are a great example of biogeography. Changes have occurred based on how the world’s geography has changed through hundreds of years and how these changes have affected which plants grew at a place and which animals lived.
- Fossils
Even though the fossil record is known to be very incomplete, paleontologists have found many examples of transitional stages in the origin of higher taxa, such as tetrapod, birds, mammals. Critically important intermediates are still being found, such as ancestors of modern turtles. Many discoveries in the fossil record fit predictions based on phylogenetic or other evidence. Prokaryotes precede eukaryotes in the fossil record. Fossils provide solid evidence that organisms from the past are not the same as those found today. A fossil record is a collection of fossils preserved in sedimentary rock. Fossil records can change over time as the world changes.
Through fossils, the extinct and the endangered species can be studied. In addition to this, radiometric dating is used to determine how old the fossil may be. One of the best examples of fossils is the evolution of horses –
This picture shows the evolution of horses over the past 55 million years. Transition of Horse feet is also an important study section in the evidence for evolution through the fossil record. There may be a few missing links, but it still has provided us with a history of horse life.
- Molecular Biology
The evidence for evolution comes from all realms of biology, especially molecular biology. Similarities between cells and molecules can tell us about similarities in ancestry. All living organisms have DNA, genomes, gene expression, amino acids. A cell is a building block of a living organism and genetic codes inside these cells is one of the strongest support biology can provide for a common ancestor. In the example of horses in the previous section, a lot of the evolution of horses over the years was related to the domestication of horses. Archaeologists were highly unsure if the domestication happened in just one community or in multiple areas 6000 years ago. It seems to have started around the Black Sea around Ukraine and Kazakhstan. Molecular biology techniques such as DNA sequencing is used to gain a complete knowledge of the order of nucleotides in horses. A lot of diversity was observed in wild horses. Mitochondrial DNA showed that horses must have been domesticated in more than just one community. The mitochondrial DNA showed similarities with some other animals as well which lived in different areas and timelines.
In 1959, scientists at Cambridge University studied that organisms that are more closely related should have more similarities in their amino acid sequences in myoglobin. Molecular evidence can be used to build a phylogenetic tree. This can be used to compare the amino acid differences in different animals and hence their ancestry.
- Direct Observation
Direct observation is a method of data from surroundings without any alterations. In today’s day and age, so many hypotheses can be tested using direct observation. We can infer patterns and processes by comparing the outcomes of experiments with previously made hypotheses. Mendel’s laws are a good example of this comparison as each scientist and study is committed to some kind of a hypothesis. Evidence for evolution through direct observation will always stay relevant regardless of the time and age.
The resistance of mosquitoes against the pesticide DDT is a classic example of direct observation. Over the years since 1950, mosquitoes that were least or not at all resistant were eliminated due to natural selection (survival of the fittest). The population of mosquitoes had naturally occurring variations in alleles that made them resistant to DDT. Humans are no longer able to use DDT to eliminate mosquitoes.
In conclusion, evidence from comparative anatomy (homologous structures, vestigial structures, and embryological structures), molecular biology, the fossil record, biogeography, and direct observation support the theory of evolution. The evidence of the theory of evolution is established from a scientific point of view using biological tools such as genetics, and radiocarbon dating. My opinion coincides with the hypotheses of this paper which was to study the evidence for evolution. After doing the research, I am certain about the theory of evolution. Evolution may be convergent or divergent but either way, evolution occurred over the years and there is evidence for it.
“What Is the Tree of Life?: Tree of Life : Exhibits : Yale Peabody Museum of Natural History.” What Is the Tree of Life? | Tree of Life : Exhibits : Yale Peabody Museum of Natural History, 12 June 2015, peabody.yale.edu/exhibits/tree-of-life/what-tree-life.
“Biogeography.” Biogeography – an Overview | ScienceDirect Topics, www.sciencedirect.com/topics/agricultural-and-biological-sciences/biogeography.
Wiens, John J., et al. “The Niche, Biogeography and Species Interactions.” Philosophical Transactions of the Royal Society B: Biological Sciences, 27 Aug. 2011, royalsocietypublishing.org/doi/full/10.1098/rstb.2011.0059.
Dawson, Michael N et al. “An horizon scan of biogeography.” Frontiers of biogeography vol. 5,2 (2013): fb_18854.
Podhajsky, Alois Wilhelm, and E. Gus Cothran. “Origin of Horse Domestication.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., 16 Mar. 2020, www.britannica.com/animal/horse/Origin-of-horse-domestication.
“Molecular Biology.” Evidence for Evolution – Biology 3.5, evidenceforevolution13bio.weebly.com/molecular-biology.html.
“Vestigial Structures – Evolution.” Google Sites, sites.google.com/site/brandtevolution/home/mutation.
“Wild Horses, Evolution, Conjecture.” Photojournalist – Journalist, 23 Aug. 2016, prophoto7journal.wordpress.com/2016/08/22/wild-horses-evolution-conjecture/.
Rajvi Agravat 