6-1 Darwin’s Discovery

Charles Darwin Charles Darwin ◊Charles Darwin was a naturalist (a person who studied the natural world) who in 1831, sailed on the ship, the Beagle, around the world. ◊During this voyage, he observed plants and animals he never saw before and wondered why they were so different from those in England. ◊Charles Darwin was a naturalist (a person who studied the natural world) who in 1831, sailed on the ship, the Beagle, around the world. ◊During this voyage, he observed plants and animals he never saw before and wondered why they were so different from those in England.

Charles Darwin (cont.) ◊He stopped in South America and was amazed at the diversity (variety) of species he observed. ◊A species is a group of similar organisms that can mate with each other and produce fertile offspring. ◊He also found the bones of extinct animals that resembled animals he knew like giant sloths similar to the small sloths alive today ◊He stopped in South America and was amazed at the diversity (variety) of species he observed. ◊A species is a group of similar organisms that can mate with each other and produce fertile offspring. ◊He also found the bones of extinct animals that resembled animals he knew like giant sloths similar to the small sloths alive today

Charles Darwin (cont.) ◊In 1835, he reached the Galapagos Islands off the coast of South America and was surprised to see there were many animals and plants similar to the ones found on the mainland. But, he observed there were important differences too. Like iguanas that fed on seaweed or cormorants (water birds) that had such small wings they couldn’t fly. ◊From these observations, he inferred that these animals had originally came from the mainland and over time they became different from their ancestors. ◊In 1835, he reached the Galapagos Islands off the coast of South America and was surprised to see there were many animals and plants similar to the ones found on the mainland. But, he observed there were important differences too. Like iguanas that fed on seaweed or cormorants (water birds) that had such small wings they couldn’t fly. ◊From these observations, he inferred that these animals had originally came from the mainland and over time they became different from their ancestors.

Mainland Animals vs Galapagos Species

AdaptationsAdaptations ◊Darwin noticed the finches on the island while similar to ones on the mainland but that many had differences (like beak shapes) that made them suited to the life they led. ◊For example, some that fed on insects had thin, needlelike beaks. Ones feeding on seeds had short, thick beaks. ◊He called these differences Adaptations. ◊He called these differences like beak shape Adaptations. ◊Adaptations are traits that help an organism survive in a particular environment and reproduce. ◊Darwin noticed the finches on the island while similar to ones on the mainland but that many had differences (like beak shapes) that made them suited to the life they led. ◊For example, some that fed on insects had thin, needlelike beaks. Ones feeding on seeds had short, thick beaks. ◊He called these differences Adaptations. ◊He called these differences like beak shape Adaptations. ◊Adaptations are traits that help an organism survive in a particular environment and reproduce.

Galapagos Finches

EvolutionEvolution ◊After Darwin returned home he continued to think about his observations and how the animals with different adaptations arose on the Galapagos. ◊He reasoned that when the animals arrived on the Islands they found living conditions different then those on the mainland. He thought that over time, each species changed and became better adapted to the new conditions. ◊The gradual change in a species over time is called evolution. ◊His ideas are referred to as the theory of evolution. ◊A scientific theory is a well tested concept that explains a wide range of observations. ◊After Darwin returned home he continued to think about his observations and how the animals with different adaptations arose on the Galapagos. ◊He reasoned that when the animals arrived on the Islands they found living conditions different then those on the mainland. He thought that over time, each species changed and became better adapted to the new conditions. ◊The gradual change in a species over time is called evolution. ◊His ideas are referred to as the theory of evolution. ◊A scientific theory is a well tested concept that explains a wide range of observations.

Evolution (cont.) ◊Darwin knew that people used selective breeding to produce organisms with desired traits and that a similar process must happen in nature. ◊Darwin proposed that these changes occur as a result of natural selection. ◊Natural selection is a process by which individuals that are better adapted to their environment are more likely to survive and reproduce than other members of the same species. ◊Darwin identified three factors that affect the process of natural selection: overproduction, competition, and variations. ◊Darwin knew that people used selective breeding to produce organisms with desired traits and that a similar process must happen in nature. ◊Darwin proposed that these changes occur as a result of natural selection. ◊Natural selection is a process by which individuals that are better adapted to their environment are more likely to survive and reproduce than other members of the same species. ◊Darwin identified three factors that affect the process of natural selection: overproduction, competition, and variations.

Natural Selection ◊Overproduction is where a species like insects or turtles produce many more offspring than can survive on the available resources (like food, living space, or water). ◊Since these resources are limited, the offspring must compete against each other to survive. This is competition. Some will be better than others at getting food to eat or at escaping predators. ◊As a consequence, only a few will survive long enough to reproduce. ◊Overproduction is where a species like insects or turtles produce many more offspring than can survive on the available resources (like food, living space, or water). ◊Since these resources are limited, the offspring must compete against each other to survive. This is competition. Some will be better than others at getting food to eat or at escaping predators. ◊As a consequence, only a few will survive long enough to reproduce.

Natural Selection (cont.) ◊Remember from your study of genetics, members of a species differ from each other in many of their traits. ◊The differences between individuals of a species is called variation. ◊Some variations make an individual better adapted to their environment and more likely to survive and reproduce. Their offspring may inherit the allele for the helpful trait. In effect, the environment has selected for the individuals with the helpful trait to be the parents of the next generation. ◊Remember from your study of genetics, members of a species differ from each other in many of their traits. ◊The differences between individuals of a species is called variation. ◊Some variations make an individual better adapted to their environment and more likely to survive and reproduce. Their offspring may inherit the allele for the helpful trait. In effect, the environment has selected for the individuals with the helpful trait to be the parents of the next generation.

Natural Selection (cont.) ◊Over a long period of time, natural selection can lead to evolution. Helpful variations gradually accumulate in a population, while unfavorable ones disappear. ◊For example, suppose a fast moving predator moves into a turtle’s habitat. The turtles that can swim faster are more likely to avoid being eaten and reproduce. Over time, more and more turtles of that species would have the fast swimming trait. ◊Over a long period of time, natural selection can lead to evolution. Helpful variations gradually accumulate in a population, while unfavorable ones disappear. ◊For example, suppose a fast moving predator moves into a turtle’s habitat. The turtles that can swim faster are more likely to avoid being eaten and reproduce. Over time, more and more turtles of that species would have the fast swimming trait.

The Role of Genes in Evolution ◊ Without variations, all the members of a species would have the same traits and evolution would not occur because all members would have an equal chance of surviving and reproducing. ◊Variations are the result of mutations in genes or the shuffling of alleles during meiosis. ◊As a result, only traits that are inherited or controlled by genes, can be acted on by natural selection. ◊ Without variations, all the members of a species would have the same traits and evolution would not occur because all members would have an equal chance of surviving and reproducing. ◊Variations are the result of mutations in genes or the shuffling of alleles during meiosis. ◊As a result, only traits that are inherited or controlled by genes, can be acted on by natural selection.

Evolution in Action ◊For example, prior to the industrial revolution, light colored peppered moths made up most of the species. Their coloration enabled them to blend into the light colored backgrounds of trees and avoid being eaten by birds. ◊After the industrial revolution and years of soot blackening the trees, black peppered moths made up most of the population. This is because now light-colored moths showed up against the dark background and were eaten by birds and black ones could blend in. ◊For example, prior to the industrial revolution, light colored peppered moths made up most of the species. Their coloration enabled them to blend into the light colored backgrounds of trees and avoid being eaten by birds. ◊After the industrial revolution and years of soot blackening the trees, black peppered moths made up most of the population. This is because now light-colored moths showed up against the dark background and were eaten by birds and black ones could blend in.

Peppered Moths: Light phase and Dark phases

How Do New Species Form ◊Darwin’s theory of evolution by natural selection explains how variations lead to changes in a species. ◊But what about the formation of an entirely new species? Scientists have found that geographic isolation is one of the main ways this can happen. If a group of organisms gets separated from the main group long enough to evolve different traits a new species may form. For example, a river or mountain range may isolate a group of organisms so that in time they may evolve traits that make them distinctive (different) from their main group. ◊Darwin’s theory of evolution by natural selection explains how variations lead to changes in a species. ◊But what about the formation of an entirely new species? Scientists have found that geographic isolation is one of the main ways this can happen. If a group of organisms gets separated from the main group long enough to evolve different traits a new species may form. For example, a river or mountain range may isolate a group of organisms so that in time they may evolve traits that make them distinctive (different) from their main group.

Continental Drift ◊Geographic isolation may also occur on much larger scales. ◊For example, continental drift causes the movement of crustal plates. This may push once connected landmasses apart so that their species get separated and evolve separately. ◊Geographic isolation may also occur on much larger scales. ◊For example, continental drift causes the movement of crustal plates. This may push once connected landmasses apart so that their species get separated and evolve separately.

Continental Drift (cont.) ◊Australia is a good example, where most of its mammals are marsupials (bear their young in pouches) where marsupials have been mostly replaced by placental mammals almost everywhere else. ◊Madagascar is another good example, where the island split off from Africa so long ago most of the animals there like lemurs have become either extinct or new species have evolves so that many of the life forms there are found nowhere else. ◊Australia is a good example, where most of its mammals are marsupials (bear their young in pouches) where marsupials have been mostly replaced by placental mammals almost everywhere else. ◊Madagascar is another good example, where the island split off from Africa so long ago most of the animals there like lemurs have become either extinct or new species have evolves so that many of the life forms there are found nowhere else.