Evolution
Charles Darwin embarked on a five-year voyage around the world in 1831 on the British ship, the HMS Beagle. Darwin was a naturalist and his job was to collect and study the many living things he saw on the expedition. Off the coast of the Galapagos Islands in South America, Darwin observed about 14 different species of a bird called finches. The main disparity or differences among the finches were the size and shape of their beaks.
The finches lived on different islands and
their beaks are examples of physical
adaptations. The finches probably
derived from a common ancestor on
the mainland. However separated
by water, the type of food and habitat
on the various islands may have led to
different genetic changes among the
finches. Genetic changes take a long
time to occur. The Warbler finch has long, narrow pointed beak that is used to eat insects. Medium ground finches had larger, wider, and stronger beaks that were used to crack open seeds. Over time, the beaks of different finch species on the Galapagos Islands have become adapted for obtaining and eating different kinds of foods. Darwin also observed similarities and differences among other species of organisms that lived on the mainland and the Galapagos Islands.
The iguanas on the mainland had small short claws that were very useful for climbing trees. Their diet consisted of eating leaves. The iguanas on the Galapagos Islands ate seaweed. They had larger claws that enabled them to clutch and hang on to slippery rocks near the ocean.
Living things have bodies that are adapted for the places they live and the things they do. Fish have gills so that they can remove oxygen that is dissolved in water. Most plants have green leaves that contain chlorophyll so that they can make food. Jellyfish have stinging cells to capture prey. Birds have hollow spongy bones so that they will be light enough to fly. Arctic animals have layers of fat and thick coats of fur to keep warm in the frigid Arctic climate. There are hundreds of examples of ways that
organisms are adapted for a successful lifestyle.
Humans, too, are adapted for the things they do. One of our adaptations is our hand. Humans, as well as monkeys, gorillas, and other primates, have a hand that can grasp objects.
1. Organisms tend to produce more offspring than can survive. For example, a single salmon can lay thousands of eggs at one time. Not all of the offspring will survive to maturity. Only a few will live to be adults.
2. Individuals within a species have slight variations. If you have ever visited a pet store, you may have noticed a slight variation in the appearance of the fish in the tanks. A population of fish of the same species may differ slightly in color, length, and fin size.
3. Competition for resources occurs among individuals. Organisms within the same species struggle to survive and those best suited for the environment are more likely to survive. For example, individuals can compete for food and shelter. Individuals that can't find food or shelter will most likely not survive. Also think about a herd of gazelle grazing in Africa's savanna. The gazelle that can run fast enough to escape a predator can pass that beneficial trait to its offspring.
4. The population gradually changes when individuals who are better suited to survive and reproduce pass their genes to their offspring. After many generations, the desirable or helpful traits will be present in the majority of individuals in the population.
Some of the variation in characteristics makes some individuals better at surviving and, more importantly, better at reproducing than others. Other variations may not improve the fitness of the individual but do help the population as a whole to be more fit. A patch of wildflowers that exhibits a variety of colors may be more likely to catch the attention of more pollinating insects or birds than a patch that is all one color. Certain fish tend to school together, making it more difficult for predators to single out a single fish for capture, so all of the population benefits.
Darwin proposed that natural selection is responsible for how favorable variations are passed from one generation to the next generation. Over a long period of time these favorable variations will accumulate in a species while the undesirable or unfavorable traits will eventually disappear. Natural selection is also known as "the survival of the fittest". It means that the "fittest" organisms have adapted to their environment much better than other organisms and are able to pass their genes or traits to their offspring.
Fitness leads to natural selection that results in population level changes, not just changes in an individual. If the adaptation only benefits the current generation and does not remain in succeeding generations, it will have no effect on the population as a whole and will not cause "evolution".
Evolution occurs when advantageous genetic variations within a species are expressed at a high frequency because they have been passed on to subsequent generations. Evolution by natural selection is a gradual process that takes place over many, many generations. Some adaptations will cause speciation right away, while others simply increase the diversity of a population. A certain warbler is identical to another in every way except the "mating song." A mutation in one warbler's song led to speciation because warblers with one song attract only other warblers with the same song. They will not mate with warblers who do not have the same mating song. This one trait separates these warblers into two different species.
Evidence of Evolution
Charles Darwin's theory of evolution is the unifying concept in biology and overwhelming evidence supports natural selection. Although some disagree with the theory, pesticide-resistant insects, modern elephants, Darwin's Galápagos finches, and adaptive virus strains prove that natural selection is happening all the time.
indication that certain organisms evolved from a common ancestor. Organs or body structures which are present in an organism but have no useful purpose are called vestigial structures. In humans, the tailbone at the tip of the spine and wisdom teeth are vestigial structures. They may have had some important use in the past for our ancestors. Many mammals that have tails use them for balance and communication. The tailbone was no longer useful as our ancestors began to walk upright.
Have you had your wisdom teeth removed? The pain a person gets when their wisdom teeth come in is due to them emerging through their gum at an irregular or horizontal angle. There is usually not enough room in a person's jaw for wisdom teeth. The removal of the wisdom teeth has no adverse effect on a person's dental health or wellbeing. It is believed that our ancestors had larger jaws that could accommodate the extra teeth. Homologous structures are organs and bones that are similar in different organisms that were inherited from a common ancestor. The similar forelimb bone structure in a dog, dolphin and bird indicates that they are related. The arrangement of the bones in the dolphin's flipper, bird's wings, and the dog's leg suggests that they were inherited from an earlier vertebrate that is closely related to the three types of animals. The different species evolved from a common ancestor.
Fossil and DNA Evidence
Fossils also provide evidence of evolution. A fossil is the remains or traces of an organism that lived in the past. Fossils usually form when an organism dies and after millions of years the bones or a shell of the organism is buried in layers of sediments that becomes sedimentary rock.
Scientists can use the fossil remains of an organism to determine its feeding behavior, reproductive methods, parental care, and also what type of environment it may have lived in the past.
The four major types of fossils are:
Mold fossils (a fossilized impression made in rock)
Cast fossils (formed when a mold is filled in)
Trace fossils (fossilized nests, imprints of plants, burrows, footprints, etc.)
Preserved fossils (fossils of the actual animal or animal part preserved in ice, tar, amber, etc.)
Petrified fossils (fossilized remains in rock)
Fossils show how a species of organisms have changed over time. For example, the earliest form of a horse had four toes on each front foot. Over time, those toes became a single hoof. The fossil remains of the earliest known horse suggest that it took about 50 -55 million years for the animal to evolve from the size of a small dog to the size of a modern horse.
The diversity of life is incredible; yet what we see today is only a tiny view of all the different kinds of life that existed in the past. Fossils are windows into time that let us see what living things once were like. From the discoveries of dinosaur fossils we can learn how continents have moved, how climates and landscapes have changed and how life has evolved. Watch the following video to learn more about how we use fossils to gain a better understanding of our world. The video is approximately 25 minutes long. Pause the video when
necessary to make notes.
Humans have walked the Earth for 190,000 years. That is a mere blip in Earth's 4.5-billion-year history. A great deal has happened in that time. Earth formed and oxygen levels rose in the foundational years of the
Adaptations
Think about the way you dress in the winter. You don't wear your shorts and a bathing suit when it's snowing outside! You wear warm clothes, and maybe even a hat and mittens to protect yourself from the weather. The way you dress in the winter is a kind of adaptation. Luckily as humans, we are able to put on a jacket and gloves during the winter. The extra layer of clothing helps to protect us from the cold weather. Many other animals depend on physical adaptations.
In the previous lesson, you learned about how an animal's behavior can help it survive and reproduce in its environment. Animals also have certain physical adaptations. A trait that helps an organism survive and reproduce is called an adaptation. Physical adaptations are body structures that allow an animal to find and consume food, defend itself, and to reproduce its species. Physical adaptations help an animal survive in its environment.
Some examples of physical adaptations are:
Camouflage
Mimicry
Chemical defense
Body coverings & parts
Some insects and animals can use camouflage as a method to
blend into the environment. They do not want to attract attention or avoid being noticed by predators. For example, a chameleon
can change its color to match its surroundings. Some caterpillars can even look like bird droppings or twigs from a tree. Mimicry occurs when an organism looks or sounds like another living organism. The Viceroy butterfly uses mimicry to look like the
Monarch butterfly. The monarch is poisonous while the viceroy is nonpoisonous. Some examples of chemical defenses are venom, ink, and sprays. A skunk will spray its victim with an awful spray when it feels threaten. Claws, beaks, feet, armor plates, skulls, and teeth are a few examples of how body coverings and parts of an organism can help it survive in its environment. An elephant uses its trunk to eat, drink, wash itself, and pick things up. Did you know that a baby snake has an upper tooth? This tooth has a special function. It allows the snake to cut its way out of its shell so that it is more likely to survive and reproduce. The increase likelihood that an organism will survive due to an adaptation it has is called an adaptive advantage. The presence and use of the specialized tooth in young snakes is an adaptive advantage. If they didn't have this tooth, it would be more difficult to exit the shell of their egg and they may die.
All animals live in habitats. Habitats provide food, water, and shelter that animals need to survive, but there is more to survival than just the habitat. Animals also depend on their physical features to help them obtain food,
keep safe, build homes, withstand weather, and attract mates. These physical features are called physical adaptations. Physical adaptations do not develop during an animal's life but over many generations. The shape of a bird's beak, the number of fingers, color of the fur, the thickness or thinness of the fur, the shape of the nose or ears are all examples of physical adaptations which help different animals to survive.
Animal Impostors) as it explores the world of camouflage, including some of the methods and benefits of this important evolutionary strategy.
Animal Adaptation Activity
In the Animal Adaptation Activity, you will research the physical and behavioral adaptations achieved by certain animals that helps them survive in their habitat.
Animal Adaptation Activity
Directions: The following animals have a physical or behavioral adaptation. Complete the chart below by describing how the animals' adaptations help them survive in their habitat.
Animal The Animal's Habitat A Physical or Behavioral Adaptation How the Adaptation Helps the Animal
Giraffe Tongue
Caribou Stomach
Mountain
goat Feet
Meerkats Live together in large groups
Snowshoe
Hare Large back feet
Natural Selection
Charles Darwin accumulated a tremendous collection of facts to support the theory of evolution by natural selection. One of his difficulties in demonstrating the theory, however, was the lack of an example of evolution over a short period of time, which could be observed as it was taking place in nature. Although Darwin was unaware of it, remarkable examples of evolution, which might have helped to persuade people of his theory, were in the countryside of his native England. One such example is the evolution of the peppered moth Biston betularia.
The economic changes known as the industrial revolution began in the middle of the eighteenth century. Since then, tons of soot has been deposited on the countryside around industrial areas. The soot discolored and generally darkened the surfaces of trees and rocks. In 1848, a dark-colored moth was first recorded. Today, in some areas, 90% or more of the-peppered moths are dark in color. More than 70 species of moth in England have undergone a change from light to dark. Similar observations have been made in other industrial nations, including the United States.
Each organism has different methods of adapting to its environment. Adaptations are changes in behavior or physical structure. Some
