EVOLUTION A HISTORY AND A PROCESS
DARWIN DEVELOPED A THEORY OF EVOLUTION • Ideas From Darwin’s Time • Evolution is the changes that have altered life over a very long time. • Before Darwin’s hypotheses, there were two predominant hypotheses. • One was species were fixed in time, or did not change. • The other was that Earth was less than 10,000 years old and was unchanging
DARWIN DEVELOPED A THEORY OF EVOLUTION • Georges Buffon, a French naturalist in the mid-1700s, suggested that Earth might be older than a few thousand years by looking at fossils. • His observations concluded that the fossils and some living animals were similar but not exactly alike. • In the early 1800s, Jean Baptiste Lamarck suggested that life evolves.
DARWIN DEVELOPED A THEORY OF EVOLUTION • He explained that species are not permanent and that evolution was a process of adaptation. • Biologists today look upon adaptation as an inherited characteristic that improves the organism’s chances of survival and reproduction. • The kangaroo’s hind legs and tail are examples of adaptation.
DARWIN DEVELOPED A THEORY OF EVOLUTION • Lamarck also hypothesized an explanation for adaptation that when organisms use or not use certain body parts, certain characteristics develop, and these characteristics would be passed on to the offspring. • This idea was called inheritance of acquired characteristics. • For example, ancient kangaroos developed the powerful legs jumping and passed them on to their offspring.
DARWIN DEVELOPED A THEORY OF EVOLUTION • This characteristic would have to modify the DNA of specific genes in order to be inherited, which has yet to be proven. • Look at the bonsai tree as an example. • The Voyage of the Beagle • This was the royal navy ship that Darwin began his five year adventure in 1831, upon graduating from university.
DARWIN DEVELOPED A THEORY OF EVOLUTION • He wanted to study geology, plants and animals that were encountered while charting the coast of South America. • Darwin’s Observations • He observed and collected thousands of specimens of South American plants, animals, and fossils from many diverse ecosystems.
DARWIN DEVELOPED A THEORY OF EVOLUTION • Before his voyage, Darwin held to the belief that the concepts of fixed, or unchanged species described nature; but during the voyage his concepts changed. • Upon his return to England, he believed that species change as they adapt to their changing environment. • Throughout South America, Darwin noticed
DARWIN DEVELOPED A THEORY OF EVOLUTION the plants and animals had a South American character. • They were distinct from what he had seen in Europe. • The fossils he collected supported the hypothesis that the current species were descended from ancestral species. • The Galapagos was his nirvana.
DARWIN DEVELOPED A THEORY OF EVOLUTION • The Galapagos are volcanic islands about 900 km west of Ecuador. • He noted that there were many diverse and unique organisms. • They were similar, but different, to those he found on the mainland of South America. • He also noted difference among the organisms of each island.
DARWIN DEVELOPED A THEORY OF EVOLUTION • The inference was that the organisms adapted from the mainland to the islands where they were currently found. • Ideas From Geology • Charles Lyell, a geologist, influenced Darwin. • Lyell projected that gradual geologic
DARWIN DEVELOPED A THEORY OF EVOLUTION changes could explain the physical features of today’s Earth. • Examples could include erosion of riverbeds over, maybe, millions of years that could result in canyons. • Earthquakes could cause mountain ranges to push up slowly over millions of years.
DARWIN DEVELOPED A THEORY OF EVOLUTION • This would have to mean that the Earth was much older than previously thought. • Darwin personally experienced an earthquake while in Chile. • He collected ocean fossils high in the Andes, and thought that earthquakes lifted the sea floor to the mountains, and brought with it the marine fossils.
DARWIN DEVELOPED A THEORY OF EVOLUTION • Two conclusions related to geology were drawn. • First, mountain building and erosion indicted Earth being very old. • Second, the slow and gradual processes occurring over long periods of time could cause vast changes on Earth. • This gradual change in geology led to Darwin’s evolution hypothesis.
DARWIN DEVELOPED A THEORY OF EVOLUTION • Darwin Publishes His Theory • Upon return to England, Darwin became convinced that earth was very old and species can change through time or adapt. • He read Thomas Malthus’ theories about human suffering due to disease, famine, and homelessness or populations grow too fast (reach their carrying capacity) and outgrow their resources.
DARWIN DEVELOPED A THEORY OF EVOLUTION • Darwin applied this to all species. • In 1844, Darwin wrote his thesis outlining his ideas but held on to it in order to accumulate more evidence, consult with his peers, and receive favorable public press. • Then, in 1858, another British naturalist, came to the same conclusion independently working in Malaysia, causing Darwin to publish his book The Origin of the Species a year later.
DARWIN DEVELOPED A THEORY OF EVOLUTION • Darwin’s Two Main Points • First, species on Earth originated from ancestral species. • Descendants or earliest organisms spread into different habitats over millions of years and, there, accumulated different modifications (adaptations) to the diverse ways of life. • This he called this decent with modification.
DESCENT WITH MODIFICATION: HARE vs. JACKRABBIT Large ears of jackrabbit are adaptation to hot environment that allow it to cool off, while the white fur of the snowshoe hare camouflages the animal.
DARWIN DEVELOPED A THEORY OF EVOLUTION • Second, he argued that natural selection was the mechanism for evolution. • This also is known as survival of the fittest. • This is the process by which individuals well suited to their environment reproduce more than those that are not. • Therefore, “Darwin’s theory of evolution” is really natural selection.
DARWIN DEVELOPED A THEORY OF EVOLUTION • The result of natural selection is adaptation and is another way of defining evolution. • Evolution can also mean the history of life on Earth, from the earliest microbes to the complexity of organisms found today.
REVIEW: CONCEPT CHECK 14.1, page 298 • How did the work of Lyell and Malthus influence Darwin as he developed his theory of evolution? • What characteristics of the Galapagos Islands were particularly important for Darwin? • What is natural selection? • Which of the following is an adaptation: the sharp teeth of a house cat, or a scar on the cat’s ear? Explain.
EVOLUTION HAS LEFT MUCH EVIDENCE • The Fossil Record • Fossils, as you know, are preserved remains of organisms that lived in the past. • Most are found in sedimentary rocks. • These are formed from sand and silt that has eroded from the land and deposited and
EVOLUTION HAS LEFT MUCH EVIDENCE carried by waterways to the seas and swamps, where they settle to the bottom. • Over a long period of time, there comes to be lots of this material piling up on top of one another, compressing the older sediments on the bottom into rock. • Layers, or rock strata, form when the rates of sedimentation or types of particles forming the sediments vary over time.
EVOLUTION HAS LEFT MUCH EVIDENCE • Fossils form if they are caught in the sediment after they die and are preserved. • The oldest layer are at the bottom and youngest at the top. • The fossil record is the chronologic collection of the remains within each layer, and provides historical evidence of Earth’s changing life.
EVOLUTION HAS LEFT MUCH EVIDENCE • The oldest fossil (chemical traces) was found in Greenland and dates to 3.8 billion years ago. • The first life on Earth was prokaryotes (bacteria and archaea) found in rocks about 3.5 billion years old. • The younger layers of rock give the evolution of the various eukaryotic organisms.
EVOLUTION HAS LEFT MUCH EVIDENCE • The first nuclear cell, a single cell, was found to be 1.5 billion years old. • Extinct species’ fossils aid in reconstructing the earliest days on Earth. • Paleontologists, who study ancient life, have found that whales evolved from land animals that had four limbs, but lost the hind limbs eventually.
EVOLUTION HAS LEFT MUCH EVIDENCE • Geographic Distribution • Darwin noticed the differences and similarities of organisms on the different continents he visited. • From these observations, he thought that the modern organisms evolved from those in the past. • He questioned the similarity between animals
EVOLUTION HAS LEFT MUCH EVIDENCE of the South American tropics and the animals of the South American desert; and their non-similarity to animals in the African tropics. • Why do most of the marsupials (pouched mammals) live in Australia and few placental animals (complete their embryonic development before birth), deer and squirrels, live there.
EVOLUTION HAS LEFT MUCH EVIDENCE • Placental mammals can thrive in Australia. • The belief is that the diverse marsupial species evolved from marsupial ancestors on an island continent where no placental animals were found. • Geography , according to Darwin, played a strong part in what organisms were found where.
EVOLUTION HAS LEFT MUCH EVIDENCE • Islands with similar climates in different parts of the world contained in the past and present organisms that identify with the closest large land masses. • Similarities in Structure • There are similarities among structures of different species that provides evidence of evolutionary history.
EVOLUTION HAS LEFT MUCH EVIDENCE • All mammals have the same skeletal parts in their forelimbs, but the functions might be different. • For example, there are similarities in structure between the bat’s wing and the whale’s flipper, but the function couldn’t be more different. • Similar structures in species that share a common ancestor are homologous structures.
EVOLUTION HAS LEFT MUCH EVIDENCE • Looking at homologous structures supports the evidence that adaptation takes place from the ancient species to the more modern species. • Similar structures take on new functions with adaptation which supports the descent with modification theory. • Another interesting fact is vestigial structures,