Biological Evolution: “Change in the genetic composition of a population during successive generations (due partly to natural selection) and resulting in the development of new species” (Webster’s). The ancestors of the horse, for example, have undergone considerable change in physical size and proportions over the last 60 million years. The adult size, shape, bones, internal organs and many other physical and behavioral features have changed. The original Eohippus was thus a different “type of animal” (species) than the present day horse (Equus) Such changes in body parts are the result of changes in genes. When nature “selects” the “fittest” for survival and reproduction, it is also selecting the fittest combination of genes to survive and reproduce. These come “packaged” in a creature’s body. Biological Evolution happens through transmission of genetic characteristics from one generation to the next Individuals who are the most genetically “fit”, survive to reproduce (called natural selection or “survival of the fittest”) and pass on their fit characteristics “Natural selection” is a metaphor which Darwin compared to “artificial selection” (the breeding of plants & animals). Artificial selection = humans “select” which individual plant or animal will reproduce. Natural selection = nature does this “selecting”. Varieties of bananas produced by artificial selection Note how all these dramatically different vegetables were created by artificial selection from an original ancestor. How does Natural Selection work? Four main Principles of Natural Selection • 1. Variation tendency for individuals in a species to differ slightly from their parents and from each other (genetic recombination/mutations). • 2. Overproduction While having many offspring raises the chance that some will survive, not all will survive due to competition for resources. • 3. Adaptation Certain variation allows an individual to survive better than other individuals it competes against. More successful individuals are “naturally selected” to live longer and produce more offspring that share those adaptations for their environment. • 4. Descent with Modification Over time, natural selection will result in species with adaptations that help it survive and reproduce. More individuals will have the trait in subsequent generations, as long as the environmental conditions remain the same. Important Note: Adaptations do not give an individual or species what they “need” to survive. The “best” or most “fit” features are “naturally selected” An adaptation is a structure, behavior or physiological process Help an organism to survive and reproduce in particular environment Adaptations are inherited from their parents It also refers to the ability of living things to adjust to different conditions within their environments. Structural adaptation involves some part of an organism's body. Teeth Body coverings Shells Quills Scales Camouflage Mimicry Camouflage allows an animal to blend into its environment. Makes it hard for enemies to single out individuals Mimicry allows one animal to look, sound, or act like another animal to fool predators into thinking it is poisonous or dangerous. Vascular-stems Root systems Thorns Leave type Broad:absorb more sunlight Small needle-like: reduce water loss Waxy: reduce water loss, protect from fire Poisonous/toxins Behavior adaptations include activities or behaviors that help an animal survive. 1. Innate 2. Learned 3. Survival 4. Seasonal INNATE Inherited through the genes Examples Flying for bees, birds Swimming for fish Walking for humans Speaking for humans LEARNED Learned from experience or from observing other animals Examples Type of language spoken for humans Riding a bicycle 1. 2. 3. 4. 5. Finding food Predator-Prey adaptations Predator-animals that eat other animals Prey-animal being eaten Marking Territory Way that animals inform other animals that an area is occupied Defensive Action Protect resources, themselves, food, mates, offspring Courtship Behaviors used to find a mate Parenting Depend on parents for survival Some animals use these methods of defense to protect themselves: Camouflage Snake Mimicry Mexican Milk Snake Bright colors Skunk and Poison Arrow Frog “Hair” projections Hedgehog quills Deer Antlers Help 1. 2. 3. 4. organisms adapt to the environment Migration Hibernation Estivation Biological Clock Behaviors controlled by the brain Reflexes Blinking Pain Swallowing Tolerance to a certain poison Logical thinking Warm-blooded All have some type of “hair” Some are very specialized, such as white polar bear fur Care for young Leg Length Roseate Spoonbill (top right) Foot Webbing Laughing Gull (top left) Beak Shape Long Billed Curlew (bottom) cold- blooded Scales Some undergo hibernation and estivation Lay eggs on land Leg structure and position Cold-blooded Lay eggs in water Partially of fully webbed feet Have lungs or can absorb oxygen through their skin Depends on reproductive success Operates on a population, NOT on an individual Dynamic between genetic change and the changing environment Environment exerts selective pressure: environmental conditions that select for certain individuals and select against others Natural Selection can take time or can happen quickly Fossils • Allow us to visually see organisms change over time Geography • Being able to see the distribution of organisms around the world Embryology • Similar features of embryos in very different organisms suggest evolution from a distant common ancestor Anatomy • Homologous structures – features that are similar in structure but appear in different species offers strong evidence for common descent. Vestigial structures • Underdeveloped or unused features are remnants of organs or structures that had a function in an early ancestor. Snakes have tiny pelvic bones that are homologous to lizards but are not needed. Ostrich has wings that have little or no use now.