Patterns of Macroevolution

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Patterns of Macroevolution

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Evolution of life. Getty/De Agostini Picture Library

New species evolve through a process called speciation. When we study macroevolution, we look at the overall pattern of change that caused the speciation to occur. This includes the diversity, speed, or direction of the change that caused the new species to emerge from the old one.

Speciation generally happens at a very slow pace. However, scientists can study the fossil record and compare the anatomy of previous species with that of today's living organisms. When the evidence is put together, distinct patterns emerge telling a story of how speciation probably happened over time.

 

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Convergent Evolution

Booted Racket Tail Hummingbird. Soler97

The word converge means "to come together". This pattern of macroevolution happens with distinctly different species become more similar in structure and function. Usually, this type of macroevolution is seen in different species that live in similar environments. The species are still different from one another, but they often fill the same niche in their local area.

One example of convergent evolution is seen in North American hummingbirds and Asian fork-tailed sunbirds. Even though the animals look very similar, if not identical, they are separate species that come from different lineages. They evolved over time to become more alike by living in similar environments and performing the same functions.

 

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Divergent Evolution

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Piranha. Getty/ Jessica Solomatenko

Nearly the opposite of convergent evolution is divergent evolution. The termdiverge means "to split apart". Also called adaptive radiation, this pattern is the typical example of speciation. One lineage breaks into two or more separate lines that each give rise to even more species over time. Divergent evolution is caused by changes in the environment or migration to new areas. It happens particularly quickly if there are few species already living in the new area. New species will emerge to fill the available niches.

Divergent evolution was seen in a type of fish called the charicidae. The jaws and teeth of the fish changed based on available food sources as they inhabited new environments. Many lines of charicidae emerged over time giving rise to several new species of fish in the process. There are about 1500 known species of charicidae in existence today, including piranhas and tetras.

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Coevolution

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Bee collecting pollen. Getty/Jason Hosking

All living things are affected by the other living organisms around them that share their environment. Many have close, symbiotic relationships. The species in these relationships tend to cause each other to evolve. If one of the species changes, then the other will also change in response so the relationship can continue.

For instance, bees feed off of flowers of plants. The plants adapted and evolved by having the bees spread the pollen to other plants. This allowed the bees to get the nutrition they needed and the plants to spread their genetics and reproduce.

 

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Gradualism

The Phylogenetic Tree of Life. Ivica Letunic

Charles Darwin believed that evolutionary changes happened slowly, or gradually, over very long periods of time. He got this idea from new findings in the field of geology. He was certain that small adaptations built up over time. This idea came to be known as gradualism.

This theory is somewhat shown through the fossil record. There are many intermediate forms of species leading to those of today. Darwin saw this evidence and determined that all species evolved through the process of gradualism.

 

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Punctuated Equilibrium

Phylogenies. Getty/Encyclopaedia Britannica/UIG PREMIUM ACC

Opponents of Darwin, like William Bateson, argued that not all species evolve gradually. This camp of scientists believe that change happens very rapidly with long periods of stability and no change in between. Usually the driving force of change is some sort of change in the environment that necessitates a need for quick change. They called this pattern punctuated equilibrium.

Like Darwin, the group that believes in punctuated equilibrium looks to the fossil record for evidence of this phenomena. There are many "missing links" in the fossil record. This lends evidence to the idea that there really aren't any intermediate forms and large changes happen suddenly.

 

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Extinction

Tyrannosaurus Rex Skeleton. David Monniaux

When every individual in a population has died off, an extinction has occurred. This, obviously, ends the species and no more speciation is able to happen for that lineage. When some species die out, others tend to flourish and take over the niche the now extinct species once filled.

Many different species have gone extinct throughout history. Most famously, the dinosaurs went extinct. The extinction of the dinosaurs allowed mammals, like humans, to come into existence and thrive. However, descendants of the dinosaurs still live on today. Birds are a type of animal that branched off from the dinosaur lineage.

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Your Citation
Scoville, Heather. "Patterns of Macroevolution." ThoughtCo, Jul. 30, 2015, thoughtco.com/patterns-of-macroevolution-1224823. Scoville, Heather. (2015, July 30). Patterns of Macroevolution. Retrieved from https://www.thoughtco.com/patterns-of-macroevolution-1224823 Scoville, Heather. "Patterns of Macroevolution." ThoughtCo. https://www.thoughtco.com/patterns-of-macroevolution-1224823 (accessed May 26, 2018).