Hypothesis of early Earth • About 4.4 billion years ago, Earth might have cooled enough for the water in its atmosphere to condense. • This might have led to millions of years of rainstorms with lightning, enough rain to fill depressions that became Earth’s oceans. • The oldest rocks dated are 3.9 million years old.
Forming fossils • Organisms usually have to be buried in mud, sand, or clay soon after they die. • It is not likely that each species that ever existed will be fossilized. • Most fossils are found in sedimentary rocks.
What has been learned from fossils • The geologic time scale begins with the formation of Earth about 4.6 billion years ago.
Continental drift • Earth’s continents have moved during Earth’s history and are still moving today at a rate of about six centimeters per year. • The theory for how the continents move is called plate tectonics.
Early ideas about origin of life • spontaneous generation: nonliving material can produce life • Redi disproved this idea in 1668. • Pasteur also disproved this idea in the 1800s. He solidified that idea that life begets life.
Scientific hypotheses of life’s origins • First, simple organic molecules, or molecules that contain carbon, must have formed. • Then these molecules must have become organized into complex organic molecules such as proteins, carbohydrates, and nucleic acids that are essential to life. • Oparin experiment: energy from the sun, lightning, and Earth’s heat triggered chemical reactions to produce small organic molecules from the substances present in the atmosphere
Primordial soup • Rain probably washed the molecules into the oceans to form what is often called a primordial soup • In 1953, two American scientists, Stanley Miller and Harold Urey, tested Oparin’s hypothesis by simulating the conditions of early Earth in the laboratory.
Protocell • Protocell: membranous structures capable of growth and reproduction • The work of American biochemist Sidney Fox in 1992 showed how the first cells may have occurred. • Likely the first cells were anaerobic, unable to use oxygen and able to use organic materials in the oceans as energy.
Archaebacteria • Prokaryotic • Live in harsh environments, such as deep-sea vents and hot springs • Used sulfur as energy to make glucose (sugar)
Theory of evolution • Charles Darwin’s theory is the core of modern biology. • His idea explains how organisms have changed over time, not how the first organisms on Earth came to be. • Evolution is a theory and not a hypothesis.
Misconceptions of evolution • Many people think that Darwin’s theory states that man evolves from monkeys or apes. • This is untrue. Evolutionary theory suggests that humans and all primates share some common ancestors in the past. • Many people think that evolution disproves religion. • This is untrue. Evolution cannot prove or disprove religion. Evolution only states how species can change genetically over time.
Misconceptions of evolution • Many people think that Darwin invented evolution. • This is untrue. Alfred Russell Wallace proposed the concept of “survival of the fittest.” Jean Baptiste Lamarck proposed the “use or disuse” hypothesis. Because Lamarck’s work was scientifically unsound, many confuse Lamarckian evolution with Darwinian evolution. Lamarck believed that if, for example, the trees are tall, horse-like animals could grow simply long necks to eat the leaves, therefore evolving a giraffe.
Misconceptions of evolution • Many people believe that evolution always changes a species to make the species better. • This is untrue. Evolution is a process that shows species can change over time. Whatever genes are best adapted for survival in a given time period will survive and be passed onto future generations. These environment in the future may be very different, and the genes passed down may no longer be best adapted to the environment.
Evidence for evolution • DNA analysis • Fossil records • Morphological comparisons • Embryology
Darwin on the HMS Beagle • He began in 1831 at age 22 when he took a job as a naturalist on the English ship HMS Beagle, which sailed around the world on a five-year scientific journey.
Darwin on the HMS Beagle • As the ship’s naturalist, Darwin studied and collected biological and fossil specimens at every port along the route. • On the Galápagos Islands, Darwin studied many species of animals and plants that are unique to the islands but similar to species elsewhere. • These observations led Darwin to consider the possibility that species can change over time.
Formulating the theory of natural selection • Darwin observed that the traits of individuals vary in populations and are inherited. • Artificial selection or breeding of specific animal and plant traits has long been practiced. • Darwin hypothesized that there was a force in nature that worked like artificial selection
Natural selection • Natural selection is a mechanism for change in populations. • It occurs when organisms with favorable variations survive, reproduce, and pass their variations to the next generation. • Organisms without these variations are less likely to survive and reproduce. • As a result, each generation consists largely of offspring from parents with these variations that aid survival. • Natural selection is what causes evolution.
Natural selection example • Fishes may differ in color, size, and speed. • Individuals with certain useful variations, such as speed, survive in their environment, passing those variations to the next generation.
Natural selection example • Over time, offspring with certain variations make up most of the population and may look entirely different from their ancestors.
Adaptation: any variation that aids an organism’s chances of survival in its environment • According to Darwin’s theory, adaptations in species develop over many generations. • Adaptations to the body’s structure within one or two generations is Lamarck’s ideas. • Remember that Lamarck believed if an animal needs more fur to stay warm and can grow more fur, this is the concept of “use and disuse” not evolution or adaptation.
Adaptation example • The ancestors of today’s common mole-rats probably resembled African rock rats.
Adaptation example • Some ancestral rats may have avoided predators better than others because of variations such as the size of teeth and claws.
Adaptation example • Ancestral rats that survived passed their variations to offspring. • After many generations, most of the population’s individuals would have these adaptations.
Adaptation example • Over time, natural selection produced modern mole-rats. • Their blindness may have evolved because vision had no survival advantage for them.
Mimicry • a structural adaptation that enables one species to resemble another species • Many harmless insects and snakes resemble harmful species, which fools predators
Mimicry • Yellow jacket hornets, honeybees, and many other species of wasps all have harmful stings and similar coloration and behavior. • Predators may learn quickly to avoid any organism with their general appearance.
Camouflage • an adaptation that enables species to blend with their surroundings • Because well-camouflaged organisms are not easily found by predators, they survive to reproduce
Evolution of drug resistant bacteria Today, penicillin no longer affects as many species of bacteria because some species have evolved physiological adaptations to prevent being killed by penicillin. Non-resistant bacterium Antibiotic Resistant bacterium When the population is exposed to an antibiotic, only the resistant bacteria survive. The resistant bacteria live and produce more resistant bacteria. If bacteria can develop drug resistance in just a few generations, imagine the changes to some bacteria over millions of years.
Fossil evidence of evolution • They provide a record of early life and evolutionary history.
Example of using fossil record Camel Evolution Oligocene 33 million years ago Miocene 23 million years ago Eocene 54 million years ago Paleocene 65 million years ago Age Present Organism Skull and teeth Limb bones
Structural features with a common evolutionary origin are called homologous structures. Homologous structures can be similar in arrangement, in function, or in both. Comparing anatomy Crocodile forelimb Bird wing Whale forelimb
Comparing anatomy • The body parts of organisms that do not have a common evolutionary origin but are similar in function are called analogous structures. • Example: Insect and bird wings probably evolved separately when their different ancestors adapted independently to similar ways of life.
Vestigial organs • a body structure in a present-day organism that no longer serves its original purpose, but was probably useful to an ancestor • Vestigial structures, such as pelvic bones in the baleen whale, are evidence of evolution because they show structural change over time.
Embryology • An embryo is the earliest stage of growth and development of both plants and animals. • The embryos of a fish, a reptile, a bird, and a mammal have a tail and pharyngeal pouches. Pharyngeal pouches Pharyngeal pouches Mammal Reptile Bird Fish
Embryology • Shared features in the young embryos suggest evolution from a distant, common ancestor Pig fetus – 21 days Human fetus – 31 days