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NATURAL SELECTION What is natural selection? the process whereby organisms better adapted to their environment tend to survive and produce more offspring So what does that mean? It means that living organisms that have genetics that are better will pass their genes on. Examples Let’s say you have 3 animals: a crocodile, rattlesnake and a rabbit. Which one will survive longest? What if I told you they were all put in a mountainous area with snow on it? What if now I told you they were all put in a swamp? So what does that mean? Does the crocodile have better genes? The rabbit? How about the rattlesnake? No, it just means that the genes they have are best suited for a particular area. Natural Selection in Four Steps Overproduction Variation Competition Selection Overproduction Each species produces more offspring that can survive 2. Variation Each individual has a unique combination of inherited traits. Adaptation: an inherited trait that increases an organism’s chances of survival Adaptations–what do you see? How about this? Why is variation important? Because the environment changes. The more variation within a species, the more likely it will survive EX: If everyone is the same, they are all vulnerable to the same environmental changes or diseases The more variation of types of species in an habitat, the more likely at least some will survive EX: Dinosaurs replaced by mammals 3. Competition Individuals COMPETE for limited resources: Food, water, space, mates Natural selection occurs through “Survival of the fittest” Fitness: the ability to survive and reproduce Not all individuals survive to adulthood 4. Selection The individuals with the best traits / adaptations will survive and have the opportunity to pass on it’s traits to offspring. Natural selection acts on the phenotype (physical appearance), not the genotype (genetic makeup) Ex: When a predator finds its prey, it is due to the prey’s physical characteristics, like color or slow speed, not the alleles (BB, Bb Individuals with traits that are not well suited to their environment either die or leave few offspring. Evolution occurs when good traits build up in a population over many generations and bad traits are eliminated by the death of the individuals. Real Life Example Which beak would get passed on? How about now? So do the animals choose to have bigger beaks? How do they become more common then? Peppered Moth During the industrial revolution manufacturing plants began to spread lots of dark, black ash throughout the cities and towns. Over time what would happen to the following moths? Why do you think that? Descent with modification Descent with Modification – each living species has descended, with changes, from other species over time. Common Descent – all living organisms are related to one another Evidence for Evolution Fossil Record Homologous Body Structures Vestigial Organs Embryology Biochemical Evidence Homologous Structures Homologous Body Structures: similar anatomy in different types of animals because of common ancestor Vestigial Organs Vestigial Organs: “leftover” traces of evolution that serve no purpose Embryology Embryology: embryos of all vertebrates are very similar early on Biochemical Evidence Biochemistry: DNA with more similar sequences suggest species are more closely related EX: Humans and chimpanzees share more than 98% of identical DNA sequences