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Evolution explains how species that are present on Earth today are modified descendants of their ancestors. This scientific theory is supported by many different types of evidence, which show how evolution is a very real and natural phenomenon.

Evolution Is Based on Evidence

No doubt you have heard of evolution. It’s a hotly debated topic right now, and there are some strongly opposing viewpoints on whether it is real or not.

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Evolution is the idea that all species on Earth are descendants of ancestors that were different from themselves.This definition is not what comes under fire; rather it’s the validity of evolution itself. Evolution is a scientific theory, and when people hear the word ‘theory,’ they tend to think of an ‘idea’ or ‘generalization.’ Basically, something that’s not concrete or scientifically founded.

But a scientific theory is very different because it is a thoroughly tested and overwhelmingly accepted explanation of natural phenomena. Because evolution is a scientific theory, it is just as valid as Newton’s theory of gravity and Einstein’s theory of relativity. You sure don’t hear those being questioned!The reason evolution warrants such high merit is because it is scientifically supported. There are several different types of evidence that support evolution.

These include biogeography, comparative anatomy, and molecular biology. Let’s take a closer look at each.


Charles Darwin was a very observant man.

Something that he paid very close attention to was the similarities and differences of various organisms and how they were spread around the world. This geographic distribution of species is called biogeography – ‘bio’ for ‘life’ and ‘geography’ for ‘lands.’It was biogeography that first triggered the idea of evolution for Darwin. He noticed that certain species on islands looked much more like the species on the nearby mainland than species on other islands farther away.

This seems somewhat counterintuitive at first. Islands are similar environments; therefore, island species should resemble each other because their habitats resemble each other.But instead, what this tells us is that island species are more closely related to species on the mainland. They once lived in the same habitat, but over time, as the islands broke free and became more isolated, the island species evolved into different species from their mainland relatives.

And we can see examples of this all over the world. For example, the Galapagos tortoise is more closely related to the chaco tortoise on the main continent of South America than any tortoises you might find on other islands that have habitats similar to the Galapagos.Another example, the marsupials in Australia, are a unique group of species that are found nowhere else on Earth. Australia was once connected to the rest of the continents but some time ago broke off and became geographically isolated. It’s because of this isolation that animals, such as kangaroos and koalas, were able to evolve separately from other common types of mammals that we find on more connected continents, like Asia or North America.Madagascar is another isolated island and was once part of Africa.

There are species on Madagascar that are found nowhere else on Earth. If all ‘island’ species were similar because of their similar environments, then we would expect to find the species of Madagascar (as well as Australia) on other islands spread throughout the world. However, this is not the case.

Even though these species are very distant relatives of African species, they are more closely related than they would be to species found on other islands with similar environments.

Comparative Anatomy

Darwin was also very observant of various structures on organisms, noticing that some species had similar body features while others were quite different. This study of differences and similarities in structures is called comparative anatomy because you are literally comparing the anatomy of various organisms.Darwin found that even if they served a different function, many species had body features that were structurally alike. This indicated to him that the structures came from a common ancestor.

These homologous features were very well studied by Darwin, and even today still scientifically provide evidence for evolution.For example, many mammals have distinct similarities in their arm or forelimb. Whales, bats, cats, and humans all use their forelimb for very different functions: whales swim, cats walk, bats fly, etc. But when you get down to the skeletal structure, the design is strikingly similar.

This indicates that all of these mammals are descendants of a common ancestor that also had a forelimb, though its function is something we can only speculate about.Comparative anatomy supports evolution most strongly when we look at embryo development in vertebrates. Birds, fish, and amphibians might not share our common mammalian forelimb, but we all start out in a very similar way. At some point during development, all vertebrates have a tail and throat pouches that resemble gills. These do actually turn into gills as fish develop, but in humans turn into parts of our ears and throats.

Our tails also disappear, but tails are retained in most other vertebrate animals.

Molecular Biology

Darwin worked hard to support his theory of evolution with good science, but his astute observations are just no match for modern technology. Today, we have methods like molecular biology, that can more definitively show relationships between organisms because instead of just comparing physical features, we can compare DNA of various organisms.

Studying evolution with molecular biology allows us to look much further into the past than is possible with comparative anatomy. Molecular biology is often used to support the work done through comparative anatomy, but the advantage is that it also gives us an idea of how closely or distantly related organisms are.For example, if two organisms have similar body features and similar DNA, this indicates that these organisms are related by a more recent common ancestor. However, if they have homologous features but their DNA is less similar, we can conclude that these organisms are related but that they split from their common ancestor much longer ago.Genes provide very strong evidence in support of evolution. You might not think humans and bacteria have anything in common, but molecular biology has shown us that we do, in fact, share some homologous genes.

Though our common ancestor is very distant in the past, this shows how much we have separated and evolved from each other since that time.

Lesson Summary

Evolution wasn’t just made up as an explanation – it was observed and studied before we even knew what it was. Putting a name on it just gave everyone a way to talk about it together. But it was real and happening long before humans were even present on Earth.Darwin traveled all over the world, and during his travels, he studied various organisms and made lots of observations that led him to his theory of evolution. He saw how biogeography, the geographic distribution of species, supported the idea that island animals were more closely related to animals on the mainland than other island animals far away, despite their similar environments.

He also saw through comparative anatomy how organisms that were related had similar body features even if those features had different functions. To him, this indicated that these organisms were descendants of a common ancestor and evolved separately through time.Molecular biology provides even stronger scientific support for evolution because we can go one step further and compare DNA of various organisms. This allows us to see into the evolutionary past, identifying both distant and not so distantly related organisms on Earth.

Learning Outcomes

Following this video lesson, you should be able to:

  • Summarize the scientific theory of evolution, and understand what a scientific theory is
  • Explain how Darwin used biogeography and comparative anatomy to support his theory of evolution
  • Describe how modern molecular biology provides support for the theory of evolution

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