Note from Mr. W: 3/27/22.

This page is still under construction as I adapt it for HS use. In the meanwhile, please go ahead and use the AP Bio/College Bio version of this tutorial. 

1. Adaptations are traits that help organisms to survive and/or reproduce

Consider this leaf insect. It’s part of a family of insects called Phylliidae. All of the species within this family are leaf mimics: they’re camouflaged to look like leaves.

Camouflage is an adaptation. An adaptation is trait that helps an organism to survive and/or reproduce. Because of their camouflage, leaf Insects less likely to be noticed and eaten by a predator. In other words, looking like a leaf helps a leaf mimic to survive and pass its genes on.

A related adaptation involves how these insects walk. They rock back and forth, making them look like leaves being blown by the wind.

Among living things, adaptations are everywhere. Here are a few more examples:

• The ability of bats to hunt their insect prey through echolocation: With their extremely high-pitched voices, bats call out into their environment. Then they listen to the echoes that bounce back. Based on the pattern of echoes, a bat can hone in on an insect flying through the air. Dolphins use a similar system to hunt their prey.

  

• The height of a redwood tree, which can grow up to 100 meters tall (300 feet) in order to reach the sunlight which powers photosynthesis.
• Snake venom. Most venomous snakes use specialized fangs to inject their venom into their prey. Once injected, the venom causes paralysis and/or massive tissue damage.
• The ability of a kestrel (a small hawk) to see ultraviolet light. This allows the kestrel to see the glowing traces of urine left on rocks and soil by mice and other rodents. Based on these traces, kestrels identify areas where they can successfully hunt for their prey.
• The camouflage of the satanic leaf gecko of Madagascar: another leaf mimic.

  

• The toxic skin of the poison dart frog of central and South America. This toxicity makes these animals extremely unpalatable to predators. To advertise their toxicity, these frogs have evolved a corresponding adaptation: warning coloration. As opposed to camouflaging themselves, they advertise themselves with coloration that signals “Don’t bother eating me: I taste terrible.”

  

Adaptations are always linked to a specific environmental context. Leaf mimicry, whether it’s in an insect or a gecko, only works as a camouflage adaptation in a leafy forest. In another environment — a treeless desert, or a forest where the leaves have fallen off the trees — looking like leaf becomes a liability. In a non-leafy environment, leaf mimicry would make survival less likely.

Adaptations are the result of a process called natural selection. To see how natural selection works, we’ll start by looking at how humans have been able to create desired traits in domesticated plants and animals.

2. Adaptations: Flashcards

3. Selective breeding, or artificial selection, parallels how adaptations arise in nature

Let’s start by answering two questions about some organisms that we’re familiar with. All of these questions are going to be related to the idea of a species: a group of organisms that can interbreed with one another to produce fertile offspring. 

What you saw above are both the results of selective breeding. In selective breeding, animal or plant breeders think of a desired trait in an animal or a plant. For many generations, breeders select organisms with that desired trait. That means that the breeders allow only those individuals with the desired trait to reproduce. The breeders, in other words, create and maintain a carefully guarded gene pool that only includes individuals with genes for the desired trait.

In the case of plants, breeders select seeds from those plants with the desired trait, and use those seeds for the next crop. The many varieties of the wild cabbage, Brassica oleracea, are an example.

Here’s how breeders took wild cabbage, and through artificial selection, created all of the varieties shown above.

• Selection the clusters at the base of the flower led to cauliflower.
• Selection for flower buds and stems led to broccoli
• Selection for lateral buds led to Brussel sprouts
• Selection for leaves led to kale.
• Selection for a thick stem led to kohlrabi.
• Selection for terminal leaf buds led to cabbage.

Note that any of these varieties can be interbred with one another. That’s because they’re all members of the same species. For example, breeding cauliflower with broccoli creates broccoflower (also known as broccoli Romanesco).

Almost all of the plants we eat came to have their current form through selective breeding or artificial selection. To focus on just one, maize or corn was first domesticated about 10,000 years ago by people living in Mexico. To domesticate means to take a wild species and to breed it so that it becomes suited to human purposes.

The wild ancestor of maize is a plant called teosinte. Teosinte is a wild grass, highly branched, with small seeds and cobs. The ancient Mexicans who bred teosinte into its modern form selected two traits: 1) larger seeds and 2) cobs with higher number of seeds. Repeating this process for many generations led to the emergence of what is now one of the most important staple crops on Earth.

In the case of animals, breeders select males and females with the desired traits, and breed them together. By continuing to select for the same trait for many generations, breeders have produced distinct varieties of dogs, cows, sheep, cats, etc.

Note that the differences between dog breeds aren’t only about looks. It’s also about behavior. Breeds like Rottweilers and boxers were bred to be protective. Collies and sheepdogs were bred for herding. Retrievers retrieve. Spaniels are hunting dogs. These behaviors are innate (though training can improve and shape a dog’s behavior). Click here to read more about the genetic basis of dog behavior (the link opens in a new tab).

Note that the words we use for the results of selective breeding are different for animals and plants. The result of animal breeding is a breed. The results of plant breeding is a variety.

Selective breeding has produced hundreds of breeds of animals and varieties of plants with desired traits. If you visit a farm and look at the animals and plants that are being grown there, that’s pretty much all that you’ll see.

A term for “trait” used in biology is phenotype, which means any observable characteristic. So, another way to formulate what happens in selective breeding is that breeders create distinct phenotypes in controlled populations of organisms.

To contrast the process of selective breeding to what happens in nature, selective breeding is also called artificial selection. Before we examine what happens in nature — the adaptation-producing process of natural selection — complete the quiz below.

4. Selective Breeding Flashcards

5. Adaptation and Selective Breeding: Checking Understanding

4. What’s Next?

1. Proceed to Natural Selection (the next HS-Level tutorial in this module)
2. Return to Thinking Like Darwin (HS-Level) Main Menu