Selecting Traits

In this lesson, students explore the phenomena of senses to uncover how certain traits give individual organisms a survival advantage. This page is a high-level extract of this lesson.

Science Background for Teachers:

Science background provides teachers with more in-depth information on the phenomena students explore in this unit about organisms and their environment. Below is an excerpt of this section from the lesson on selecting traits phenomena.

Heredity explains why baby catfish have barbels, baby hummingbirds have long, thin beaks, and baby giraffes have long necks, just like their parents. All of these are inherited traits.

The long, thin beaks of a hummingbird and the long neck of a giraffe are both examples of adaptations because they are traits that help an organism survive in its environment. An adaptation can take many generations to spread through a population. Over time, animal and plant populations can slowly adjust their diets, physical forms, and behaviors.

Minor changes to an organism’s environment can influence its ability to pass on its traits. Increased precipitation, competition for food, or invading species create situations in which only the “strongest” plants and animals survive. An organism that overcomes these minor challenges passes on its genes to the next generation. Sometimes these stresses lead to the creation of new species. New species appear when there are environmental stresses over a long period of time.

For example, there was a time, millions of years ago, when there were no giraffes. Instead, horse-like creatures, with checkered spots and short necks, roamed the African grasslands. There wasn’t much food for the short-necked animals to eat. A ground shrub was a rare find. All of the food was high in the trees. Not all of the short-necked creatures could reach the trees. Only those with the longest necks could reach the bottom-most branches. The individuals with the shortest necks had to compete for the little bit of ground food. Some were no longer able to get enough food, and died off. With each generation, necks grew longer and longer until all of the animals could eat from the tallest trees in Africa.

This is called natural selection—the theory that organisms well fitted to their environments will have offspring and pass on useful adaptations. Those organisms that cannot adapt to their environment don’t reproduce and die out over time.

The slow buildup of adaptations that leads to a new species is called evolution, a field of study associated with English naturalist Charles Darwin (1809-1882). Darwin made the connection after a survey expedition to South America, Australia, and the Galapàgos. He was particularly interested in the similarities and differences between animals in various locations, such as what made a South American mockingbird different from other species of mockingbirds.

Hints of his theory of evolution came from his observation of finches on the Galapàgos. He observed that about a dozen different finch species existed on the island, and each had a beak specific to its diet. It made him wonder how new species arise. The finches, which were confined to the island for many centuries, seemed to have descended from one species “taken and modified for different ends.”

According to evolution, one common ancestor of life on Earth gave rise to the diversity that we see documented in the fossil record and around us today. The theory of evolution suggests that we're all distant cousins: humans and oak trees, hummingbirds and whales.

Further evidence for evolution came from the field of genetics. Evolutionary biologists can identify specific genes and trace how they mutated through several related species. Human ears, for example, can be traced backward on the evolutionary timeline to fish.

A common fuel for evolution is new types of environments. For instance, when the common ancestor of Darwin’s finches traveled to the Galapàgos Islands, the population branched out as certain members became better at finding different food sources. One type of bird was the common ancestor of several new species.

Supports Grade 4

Science Lesson: Selecting Traits

In this unit students figure out the phenomena of traits in how organisms pass traits, such as the ability to sense different environmental stimuli, to their offspring. They analyze the relationship between an organism’s adaptations and its ability to survive in its environment by testing how a bird’s beak is best suited for particular kinds of food.  

Science Big Ideas

  • All organisms have traits, which are passed down from parents to offspring.  
  • Some traits help an organism survive in its environment.
  • Some variations of traits provide individual organisms with a better chance of survival in their environment.
  • An adaptation is any trait that helps an organism survive in its environment. Not all traits are adaptations because not all traits help an organism survive.  

Sample Unit CTA-2
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Science Essential Questions

  • What is the relationship between a trait and an adaptation?
  • Why is a catfish’s strong sense of taste an example of an adaptation?
  • What are some adaptations that hummingbirds have developed to help them access the energy they need to survive?
  • Why do some kinds of hummingbirds have slight differences in their beaks?
  • How do parents and their children resemble each other?
  • Why aren’t all organisms exactly the same as their parents?  
  • How is the variation of traits related to the survival chances of organisms?
  • Why do variations in traits within a population of organisms mean that some organisms are more likely to survive in a food chain than others?  
  • Why don’t, given that traits can be beneficial, all organisms develop useful traits to help them survive?  

Common Science Misconceptions

Misconception: Humans only have 5 senses.
Fact: Humans have more than 5 senses, but the 5 most commonly taught at this age are seeing, hearing, tasting, touching, and smelling.
Misconception: Individual organisms can develop adaptations in response to the environment.
Fact: Adaptations are developed over many generations.
Misconception: An organism can choose an adaptation.
Fact: Organisms cannot choose adaptations. They are specific traits that are passed down from generation to generation. They are shaped by the environment.

Science Vocabulary

Adaptation: a trait that helps an organism survive in its environment

Behavior:  an organism’s response to a stimulus

Heredity: the passing on of traits from parents to children

Inherit: to receive a trait from your parents or ancestors

Natural selection: the theory that organisms well fitted to their environments will have offspring and pass on useful adaptations

Trait:  a physical or behavioral characteristic of an organism

Lexile(R) Certified Non-Fiction Science Reading (Excerpt)

Traits and Heredity

How do organisms get traits in the first place? When parents reproduce, they pass along traits to their offspring. This passing on of traits from parents to children is called heredity. Heredity causes offspring to have traits that are similar to their parents and to their siblings.

There are patterns that occur as traits get passed along. Heredity explains why offspring look similar to their parents. This is because they inherited that trait from their parents. To inherit means to receive a trait from parents or ancestors.

Heredity explains why baby hummingbirds have long, thin beaks, just like their parents. It also explains why baby giraffes have long necks, just like their parents. Both of these are inherited traits.


Variation in Traits

However, offspring don’t look or act exactly like their parents. There are some differences. These differences are called variations. For example, one baby giraffe might have a neck that is a little shorter than its parents or siblings. Or its spots might have a slightly different color pattern than its parents or siblings.

The environment can also influence traits. For example, plants that don’t get enough water won’t grow as tall. Their leaves won’t develop as fully. Over time, they will turn brown and die. Similarly, a pet dog that is given too much food to eat will become overweight.

Sometimes variations in traits make it easier to survive, find a mate, and reproduce. For example, two different kinds of tortoises live on the Galapàgos Islands. These islands are off the western coast of South America.

On one island, the tortoises have shells that rise in the front, like a saddle. This makes it easier for them to lift their necks to reach taller cacti. Tortoises from the other island have dome-shaped shells. The vegetation is lower to the ground, so they don’t need to lift their heads as high.

Tortoises with saddle-shaped shells on the island with higher cacti benefited because they could reach the plants. They survived, and passed along the saddle shape to their offspring.

This is called natural selection. Natural selection is the theory that organisms well fitted to their environments will have offspring and pass on useful adaptations. Those organisms that cannot adapt to their environment don’t reproduce and die out over time.


Bird Beaks and Natural Selection

An English scientist named Charles Darwin was one of the first to come up with the theory of natural selection. As a young man, Darwin set off on a worldwide journey on a ship named the H.M.S. Beagle. His job on the ship was to make observations and collect samples of animals and plants from different places. Darwin was most curious about what traits animals in different locations have and don’t have in common.

He was the first to notice the difference in tortoise shells. He was also very interested in a group of finches that lived on the Galapàgos Islands. Finches are a kind of bird. He observed that there were about a dozen different finch species living on the island, and that each species had a slightly different beak. He realized that the size and shape of the beaks were directly related to the food source of each kind of finch.

This is important. Although one adaptation might be useful for one kind of bird in a specific environment, that same trait might not be useful for another species in a different environment.


Hands-on Science Activity

In this lesson, students carry out an experiment to determine how bird beaks are best suited for different types of food. Students use the data to determine how the shape of a bird beak affects the type of food a bird can eat.

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Science Standards

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Standards citation: NGSS Lead States. 2013. Next Generation Science Standards: For States, By States. Washington, DC: The National Academies Press. Neither WestEd nor the lead states and partners that developed the Next Generation Science Standards were involved in the production of this product, and do not endorse it.