Study Guide

Mechanisms of Evolution Themes

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  • Unity and Diversity

    There's a party going on right here, and it's called life. Let's celebrate. It's all right. (All lessons should come with a soundtrack.)

    Evolution has provided us with the ridiculously diverse planet. What's that? You want animals that glow in the dark? We've got that. Dracula snakes? We've got that, too. Underwater dragons? Here you go. There's more variety on Earth than can be seen in a lifetime, living on anything and everything imaginable. Every habitat on Earth is filled with different species of life. Life exists in some of the coldest, hottest, driest, wettest, and most acidic places on the planet. Hot Springs? Caves? Ocean Bottoms? Eh. No problemo. There's always a life form up for a challenge.

    Diversity is endless. There are crazy anglerfish with glowing lanterns on their heads and lizards smaller than a penny. There are carnivorous plants and flowers that smell like rotting meat. There are us. There are all the bacteria that are living in us. Don’t' underappreciate the diversity around us either, from our backyard squirrels to those weeds that obviously want to party, too.

    It's time to come together.

    With all of our differences, it's easy to forget that we have a lot in common, too. Evolution is the study of how life forms have emerged from existing life. If we broke out our etch-a-sketch and started to draw the tree of life, we'd notice that organisms are classified into three domains: Archaea, Bacteria, and Eukarya. Eukarya is further divided into kingdoms that contain animals, plants, fungi, and protists. Don't let all these classifications fool you. There's plenty of unity between all life, and that's because we all evolved from a very distant common ancestor many, many millions of years ago. Like Archaea, Bacteria, and some Eukarya, this ancestor was probably a single-celled organism, too.

    The three domains of life had a common ancestor or two.

    Bacteria, humans, plants, yeast, cockroaches…we all naturally share some common characteristics that unify us. For example, all living things have DNA. All organisms also have the ability to pass on that genetic material to offspring. We all respond to stimuli, interact with our environment, grow, and perform fundamental processes, such as DNA replication, transcription, and protein translation. And thanks to Oprah, we all evolve.

  • Structure and Function

    Guess what Batman and Flipper have in common. Go ahead. We'll wait.

    Sometimes two different organisms, arising from different ancestors and living in different places, will end up needing a similar structure for a similar function. Convergent evolution is no accident. It happens when nature independently selects for traits that multiple species need.

    Unless one of them has found its way into your belfry, bats usually live in dark places like caves. Dolphins obviously prefer the water, but it can get pretty dark in there, and it's hard to see far ahead. In order to help find their way around in the blackness, some bats, dolphins, and toothed whales use a method called echolocation to figure out where they are, where the food is, and where their friends are hanging out on Friday night.

    Some bats, dolphins, and toothed whales have coevolved to use echolocation. They send out calls, and their brain translates this information into a "visual" of their surroundings.

    These animals emit sounds and wait for their echoes to come back to them. The ultrasonic (not this Sonic) signals that are returned to their ears are translated by their brains into information about the location and size of other objects. They can then use these sounds to "see" what's out there.

    Echolocation is a prime example of convergent evolution, resulting from a similar need for a structure used for a particular function in unrelated animals. What's sweet about echolocation, however, is that these structures also evolved in a similar manner. These water- and cave-dwellers use protein products from three similar auditory genes to hear the echoes. These genes sometimes exist in other non-echolocating animals, but they are expressed at very low levels and the sequences are not as similar.

    It's fascinating that a structure-function connection in these animals arrived via convergent evolution. This occurred by a series of mutations in nearly identical genes and years of natural selection. They share genes in common even though speciation never occurred between them. Dude. They did it on their own.

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