Ch. 6-2 Theory of Evolution by Natural Selection

What We Know from Ch. 6-1 The fossil record provides evidence that change occurs over time. The fossil record provides evidence that change occurs over time. Species continue to change over time. Species continue to change over time. Biological evolution is the change over time in populations of related organisms. Biological evolution is the change over time in populations of related organisms. But how did they evolve? But how did they evolve?

Who was Charles Darwin? who in the mid- 1800s English naturalist who in the mid- 1800s developed a theory of how biological evolution works. A naturalist is a person who studies plants and animals by observing them. Spent many years studying plants and animals in their natural habitats before developing his theory. Spent many years studying plants and animals in their natural habitats before developing his theory.

His Travels At the age of 22, Darwin, a survey ship of the British Navy. At the age of 22, Darwin traveled on the HMS Beagle, a survey ship of the British Navy. Traveled all over the world, including the Traveled all over the world, including the Galapagos Islands Small chain of islands 1000 km off the west coast of South America

His Observations Noticed that – some were dry, some were more humid, and others were mixed. Noticed that each of the islands had different environment – some were dry, some were more humid, and others were mixed. He some of the islands inhabitants, including the. He studied some of the islands inhabitants, including the tortoises, mockingbirds, and finches.

Galapagos Tortoises Lived on many on the islands Lived on many on the islands Their shells differed in shape The of the shell The shape of the shell determined how far the tortoise could stretch its neck How the tortoise could stretch its neck. How far the tortoise could stretch its neck determined what food it ate. Shells close to neck could only eat low vegetation Shells close to neck could only eat low vegetation Large space between shell and neck could reach high vegetation Large space between shell and neck could reach high vegetation

Galapagos Tortoises Darwin realized there was a of the island it lived on. Darwin realized there was a relationship between each species and the food sources of the island it lived on. Became convinced that the and shared a Became convinced that the tortoise species were related and shared a common ancestor. He believed when the small ancestral tortoises came to the islands, they spread out to other islands and He believed when the small ancestral tortoises came to the islands, they spread out to other islands and over time their necks changed to match the islands’ food sources But how did this happen? But how did this happen?

Variations Darwin knew that. Darwin knew that individuals of a species had slight differences in inherited traits. These are known as These are known as variations. Ex: Even though Bengal tigers are of the same species, no two tigers have the exact same pattern. Ex: Even though Bengal tigers are of the same species, no two tigers have the exact same pattern. Ex: No two people have the exact same fingerprints! (Yes, even identical twins) Ex: No two people have the exact same fingerprints! (Yes, even identical twins)

Variations Variations in species are (caused by random changes in genes). Variations in species are caused by random mutations (caused by random changes in genes). Some mutations can Some mutations can lead to a change in phenotypes. These genetics changes to phenotypes can be. These genetics changes to phenotypes can be passed on to future generations. The tortoises were all of the same species had variations in their neck lengths and shell shapes. The tortoises were all of the same species had variations in their neck lengths and shell shapes.

Darwin’s Theory of Natural Selection Darwin knew that for the tortoises and that they needed to Darwin knew that food was a limited resource for the tortoises and that they needed to compete for food to survive. As the tortoises spread to the other various islands, some were born with random variations in neck length. As the tortoises spread to the other various islands, some were born with random variations in neck length.

Theory of Natural Selection If a (like being able to reach higher food), it would be able to than other tortoises. If a variation benefited a tortoise (like being able to reach higher food), it would be able to compete for food better than other tortoises. The tortoise would (more food = happy healthy tortoise!) The tortoise would live longer (more food = happy healthy tortoise!) Living longer = =. Living longer = reproduce more = passing on the beneficial random variation to its offspring.

Theory of Natural Selection This is Darwin’s theory of evolution by natural selection! This is Darwin’s theory of evolution by natural selection! Natural Selection is the process by which populations of organisms with variations that help them survive in their environments longer, compete better, and reproduce more than those that do not have the variations. Natural selection explains how the tortoises became matched to their food sources. Natural selection explains how the tortoises became matched to their food sources.

More evidence of Natural Selection. Darwin also studied mockingbirds and finches. He noticed that the. He noticed that the finches varied in beak shape and size. At first he thought they were different species, but then realized that the birds varied to fit what food they ate. At first he thought they were different species, but then realized that the birds varied to fit what food they ate.

Adaptations When the tortoises moved to the other islands and over many, many generations their neck length changed to fit the food source available, they adapted to the changing environment. When the tortoises moved to the other islands and over many, many generations their neck length changed to fit the food source available, they adapted to the changing environment.

Adaptations. An adaptation is an inherited trait that increases an organisms’ chance of surviving and reproducing in its environment. Three types: Three types: (color, shape, other physical characteristics) Structural (color, shape, other physical characteristics) (hunting at night, moving in herds) Behavioral (hunting at night, moving in herds) (internal body changes, like a drop in body temperature during hibernation) Functional (internal body changes, like a drop in body temperature during hibernation)

Camouflage & Mimicry Structural adaptations Structural adaptations Camouflage enables a species to blend in with its environment Mimicry is the resemblance of one species to another species Both help species avoid being eaten. Both help species avoid being eaten.

Species must adapt to an environment’s living parts and nonliving parts. What are some nonliving parts of an environment? What are some nonliving parts of an environment? Living and nonliving factors are always changing. Even slight changes affect how species adapt. What happens if a species is unable to adapt? Changing Environments

Artificial Selection Darwin selectively bred pigeons of different colors and shapes to produce new, fancy varieties. Darwin selectively bred pigeons of different colors and shapes to produce new, fancy varieties. This breading of organisms for desired characteristics is called selective breeding. He realized that changes caused by selective breeding were much like changes caused by natural selection. He realized that changes caused by selective breeding were much like changes caused by natural selection. Instead of nature selecting variations, humans did. Instead of nature selecting variations, humans did.