Evolution and Biodiversity CHAPTER 4 Evolution and Biodiversity

History of Evolution The evolution of life is linked to the physical and chemical evolution of the earth. Life on earth evolved in two phases over the past 4.7 -4.8 billion years Chemical evolution (1 billion years) of the organic molecules and systems of chemical reactions needed to form the first proto-cells. Biological evolution (3.7 billion years) of single-celled organisms and then multicellular organisms.

Evolution Evolution Evidence of Evolution theory that concerns how organisms change over time. The change in a population’s genetic makeup through successive generations. Evidence of Evolution Fossil record (most common form of evidence) Chemical analysis DNA analysis Ice core drillings

Fossil Record This stratigraphic column shows the order in which organisms appeared. Each layer represents a particular time frame and shows an organism which was found during that time. The oldest fossils appear in lower layers, and the most recent fossils at the top. This allows for placement of fossils to be used as an aid in dating the organism found.

How Has the Earth Changed? Earth is constantly changing and throughout history has had changes in The atmosphere Climate Positions of continents Geography Types and number of organisms

Atmosphere and Climate Changes in the atmosphere were the result of collisions between earth and large asteroids (catastrophic events) Climate change Alternate periods of heating and cooling Advance and retreats of ice sheets over northern hemisphere

Geologic Processes Tectonic plates have drifted atop Earth’s mantle Locations of continents and ocean basins influence Earth’s climate Species move, adapt to new environments

Patterns of Evolution Divergent evolution – the process by which related species become less alike; evolve into a variety of species Leads to speciation –the formation of a new species. Ex. Polar bears diverged from brown bears Camels and llamas Also results in adaptive radiation – the process by which members of a species adapt to a variety of habitats. Ex. Darwin’s (Galapagos) finches – 13 different variations Biodiversity is believed to be the result of speciation and extinction.

Geographic Isolation The movement of tectonic plates influences evolution by changing the locations of continents, causing some species to be geographically isolated from others. Geographic isolation – when a physical barrier separates a population into groups. can result from Mountain ranges Volcanic eruptions – lava flows Rivers Earthquakes Deforestation Continents Islands

Patterns of Evolution (cont.) 2. Convergent evolution – the process by which distantly related organisms develop similar characteristics. occurs when different species share the same environmental surroundings Ex. Whales and dolphins (mammals) now resemble fish Can often lead to cases of mimicry – the evolution of one organism so it comes to resemble or look like another. Ex. Queen Anne’s butterfly closely resembles the toxic Monarch butterfly. Over the course of time, the change of the gene pool of one species may lead to the change of the gene pool of another species – coevolution. Ex. Bats and moths

How Many? Earth has an estimated 4 – 20 million species. 1.8 million have been identified. Species – a group of similar organisms that share a common ancestor and do not reproduce outside the group.

Ways of Classifying Organisms 1. Anatomical structure The more closely related a species, the more similar their structures will be. Homologous structures – body parts with structures that are very similar, even though they have entirely different functions. Ex. Bones in a whale’s flipper, a human’s arm or bat’s wing Vestigial structures – body parts that have degenerated and seem to serve no function. Ex. Tail-bone, wisdom teeth, appendix Boas and whales – small hip and leg bones Analogous structures – body parts that have the same function but are NOT similar in structure. Ex. Wing of a bird and wing of a butterfly

Homologous Structures

Vestigial Structures Vestigial organs associated with eye structures Figure 5 Vestigial remains of a pelvic girdle in a whale Figure 6

Analogous Structures Analogous structures are a contrast to homologous structures. These structures are of no use in classifying organisms or in working out their evolutionary relationships with each other.

Ways of Classifying Organisms (cont.) 2. Chemical analysis - includes proteins, antibodies, enzymes 3. DNA analysis

How Did We Get So Many? At the Molecular Level Biological evolution By natural selection – explains how life changes over time Adaptation or adaptive traits enables an organism to survive through natural selection to reproduce under prevailing environmental conditions. Biological evolution is based on changes in a population’s genetic makeup over time. Populations evolve due to variations within, but individuals can’t develop new structures.

Darwin’s Theory Variation exists within species. All organisms compete for limited natural resources – some get more, others get less. Organisms produce more offspring than can survive. Natural selection: The environment selects organisms with beneficial traits. Individuals with adaptive traits have a greater chance than others to survive and pass on their traits to their offspring.

Processes in Which Evolution Occurs at the Molecular Level Natural selection Genetic drift – when genotypes are lost by chance; usually in small populations Artificial selection – “controlled breeding” Process controlled most directly by humans Ex. Breeding horses for speed

How Does the Genetic Makeup Change? Mutation – a change in DNA Mutations are a source of new genetic material. They add genetic material to a population’s gene pool thereby increasing variation within the population. Mutations are sometimes beneficial. Causes of mutations: Ultraviolet light X-rays Radioactivity Certain chemicals (mutagens) Random errors in DNA coding

What Limits Adaptation? A change in environment conditions can lead to adaptation only for traits already present in the gene pool of a population. Because each organism must do many things, its adaptations are usually compromises Even if a beneficial heritable trait is present in a population, that population’s ability to adapt can be limited by its reproductive capacity. Even if a favorable genetic trait is present in a population, most of its members would have to die so that individuals with the trait could predominate and pass the trait on.

Microevolution Microevolution works through a combination of four processes that change the genetic composition of a population: Mutation – involving random changes in the structure or number of DNA molecules in a cell and is the ultimate source of genetic variability in a population. Natural selection – occurs when some individuals of a population have genetically based traits that cause them to survive and produce more offspring than other individuals Gene flow – involves movement of genes between populations and can lead to changes in the genetic composition of local populations. Genetic drift – involves changes in the genetic composition of a population by chance and is especially important for small populations.

Macroevolution Macroevolution is concerned with how evolution takes place above the level of species and over much longer periods than microevolution, and macro evolutionary patterns include genetic persistence, genetic divergence, and genetic loss. Bottleneck effect – When a population suddenly reduces in size either from habitat loss, natural disaster or other changes in the environment and its genetic variation is affected. Speciation – under certain circumstances natural selection can lead to an entirely new species. Extinction – when all of one species is no longer existent.

Adaptation and the Ecological Niche Ecological niche is the species’ way of life or functional role in an ecosystem. A specie’s niche involves everything that affects its survival and reproduction. This includes.. The range of tolerance for various physical and chemical conditions The types of resources it uses, such as food or nutrient requirements How it interacts with other living and nonliving components of the ecosystems in which it is found The role it plays in the flow of energy and cycling of matter in an ecosystem.

How Does the Ecological Niche Relate to Adaptation? Evolution by natural selection leads to a remarkable fit between organisms and their environment. In terms of the ecological niche of a particular species, this fit involves having a set of traits that enables individuals to survive and reproduce in a particular environment. Species that have similar niches tend to evolve similar sets of traits, even if they are unrelated species growing in different parts of the world. Generalists and specialists

Genetic Engineering Manipulation of DNA Involves Gene-splicing Recombinant DNA Thing of miracles or Pandora’s box?