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Macroevolution: Definition, Evidence & Examples

Instructor: Dominic Corsini
This lesson teaches us about macroevolution. It focuses on the macroevolutionary approach to understanding evolution itself. Real-world examples and a brief quiz are included.

A Broader Perspective

The field of evolutionary studies tends to place considerable emphasis on small-scale changes, like minute variations in DNA, differences between subspecies, and subtle mutations. This is completely understandable (and necessary) if we're to better understand evolution as a whole. But what if we want to focus on something bigger? Perhaps study evolution through the lens of life itself? If so, we need to formulate our understanding using macroevolution.

Macroevolution refers to evolution above the species level. For example, rather than focusing on genetic variations within a single species of reptile, we might focus on reptiles in general and study why they arose in the first place.

Evidence

When we take a macroevolutionary approach to evolution, we tend to focus on major events in the history of life, like the development of reptiles, mammals or flowering plants (to name a few). Thus, it's not easy to witness macroevolution. We simply don't live long enough.

There are no firsthand accounts of when the first reptile or the first mammal arrived. So, how do we know when these events occurred? We can reconstruct them using the evidence we do have: primarily geologic data, fossils, and modern organisms. Let's use the illustration below, along with our first two pieces of evidence (geologic data and fossils), to further our understanding.

Geologic column
Geologic Column

Here we see what's called a geologic column, an illustration that depicts the history of life on Earth. To appreciate macroevolution, it's important to remember that basic evolutionary mechanisms (mutation, migration, genetic drift, and natural selection) can produce major evolutionary change when given enough time. With that in mind, let's discuss the illustration.

In geology, older layers of sedimentary rock tend to be found deeper underground. This is because they were laid down first and then covered up by additional layers. So the deeper we dig, the older things tend to get. Now, let's connect that concept to fossils.

Suppose we dug down through our geologic column and discovered the fossil of a mammal somewhere near the top. Let's also say there were no other mammal fossils anywhere below that point, but there were reptile fossils. What does this tell us? It tells us that reptiles came before mammals because reptile fossils were found in older layers of rock.

How could this be? How did reptiles give rise to mammals? Those are great questions, although the answers lie beyond the scope of this lesson. However, when we start to think that way, we're looking at things through the lens of macroevolution. Remember, macroevolution is evolution beyond the species level. It's evolution of entire groups (such as mammals or reptiles). And fossil evidence is just the start.

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