What is Comparative Anatomy? - Definition & Examples

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  • 0:03 What Is Evolution?
  • 1:52 What Is Comparative Anatomy?
  • 2:12 Homologous Structures
  • 3:03 Analogous Structures
  • 4:15 Vestigial Structures
  • 5:02 Lesson Summary
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Lesson Transcript
Instructor: Amanda Robb

Amanda holds a Masters in Science from Tufts Medical School in Cellular and Molecular Physiology. She has taught high school Biology and Physics for 8 years.

In this lesson, we'll first review evolution, then we'll look at one of the main types of evidence for evolution, comparative anatomy. We'll look at homologous, analogous, and vestigial structures, and go over examples of each.

What Is Evolution?

If you look around outside, you probably see incredible biodiversity, even in your own neighborhood. Insects crawl on plants, avoiding predators like birds and lizards. The birds themselves hide in the trees. How did all these forms of life become so unique from each other? The answer is evolution. Evolution is defined as a genetic change in a population over time. Over millions of years, one single cell evolved into all life we know today. It seems astounding, but scientists have lots of evidence for evolution. One form of that evidence is comparative anatomy - but we'll get to that later.

When organisms reproduce, some of their genes get shuffled or mixed around. This is why offspring look different from their parents. Sometimes, this shuffling causes a new trait to form that helps the organism survive. For example, let's say giraffes descended from a species with a short neck. Those short neck giraffes might have had one offspring with a little longer neck. That giraffe could reach the trees better, so it got more food, and was able to survive and reproduce. Now, the next generation of giraffes might have even longer necks. So the long neck trait is passed down because it helps the giraffe survive better. After thousands of years, all giraffes have long necks. The genetics of the population has changed and created a new species different from the short neck ancestors.

This all sounds great, but how do we know this really happened millions of years ago? Well, scientists have developed enormous amounts of evidence that evolution occurs. Today, we're going to focus on one type of evidence, comparative anatomy.

What Is Comparative Anatomy?

Comparative anatomy involves comparing the body structures of two species. 'Comparative' means to look at the similarities between two things, and 'anatomy' has to do with the structure of the body. Scientists can look at anatomical structures of seemingly unrelated animals to tell how related they are.

Homologous Structures

Homologous structures are structures that are similar in two organisms because they have a common ancestor. For example, birds, humans, bats, and even whales all have a similar arm bone structure. At first glance, you wouldn't think whales and humans are very closely related, but millions of years ago, there was one ancestor whom we are both related to. That ancestor had offspring that were all a little different, and different traits were selected for it through evolution. New species were created, and even newer species evolved from those species. However, the arm bone structure was advantageous to all the species, and so it remained in all the descendant species. Now, although we all look different, birds, bats, whales and humans all retain the arm bone structure from our ancestors.

Analogous Structures

Analogous structures are the opposite of homologous structures. Analogous structures are anatomical features of two species that look similar, or serve the same purpose, but the species are not closely related. An example of an analogous structure is bird wings and insect wings. Although both are considered wings used for flight, the anatomical structure is very different, and like we have seen, bird wings are actually more similar to human hands than to insect wings.

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