Lessons Divided by Standard EOC D.1.B Explain the biological definition of evolution.

Evolution – process by which modern organisms have descended from ancient organisms aka descent with modification Microevolution – evolutionary change below the species level, changes in the allele frequency of a population over generations Macroevolution – evolutionary change above the species level, the process of speciation over a long period of time, includes the impact of mass extinctions on the diversity of life and subsequent recovery

Clarification of Evolution Definitions Another definition for evolution is: the process by which inherited traits within populations change over time This process can eventually lead to the development of new species and new distinct populations from preexisting organisms. Individual organisms do not evolve. Populations evolve! Recall the definition of a population and species. This definition encompasses small-scale evolution microevolution (changes in gene frequency—genes determine characteristics-- in a population from one generation to the next; the change in inherited characteristics within populations over time) and large-scale evolution macroevolution (the descent of different species from a common ancestor over many generations). Evolution helps us to understand the history of life.The theory of evolution is a well-tested scientific explanation with no evidence that contradicts it. Evolution isn’t perfect and doesn’t occur linearly, going simple to complex or vice versa. Evolution can only occur based on what it is given, what variations there are, what environmental conditions there are, physical limitations of organisms (we can never have wings), etc. There might be a case where you would say, well wouldn’t it be better if…but evolution can only work on what it is given. BUT ADDRESS MISCONCEPTION. Will environmental factor that makes a physical change (sun making people tan) result in evolution? Do individuals evolve? Can an individual evolve in its lifetime (get darker skin to protect from sun?) NOOOOO! Populations evolve, not individuals. There needs to be a heritable variation that occurs by CHANCE that confers and advantage and results in those organisms surving and reproducing better and thus pass on their genes better! LONG periods of time mean hundreds and thousands and millions or years….individuals do not evolve and populations do not evolve within a single lifetime. The change in inherited characteristics might be that bears living in a warmer area have light fur, but then temperatures drop drastically so more furry bears live and over time the fur trait that is inherited is thick fur, not light fur….

Descent With Modification

Microevolution: Generation-to-generation changes in genotypes and phenotypes of populations

Macroevolution: Includes: speciation and long time scale events including extinction. Often driven by microevolution.

Early Earth and Evolution The theory of evolution expounds that 3.5 bya the first living things on Earth came into being. There was little to no genetic variation in these anaerobic prokaryotes. Mutations occurred in the genome of some which lead genetic and phenotypic variation in the population. Mutation is the original source of variation among members of the same species which provided the genetic ammunition for speciation to occur. Evolution is usually caused by the process of Natural Selection, but there are other possibilities. Natural selection is process by which individual which are more fit for the environment survive and reproduce. The result is microevolution. The gene pool experiences changes in allele frequencies.

Natural Selection to Speciation If phenotypic variation leads to increased survival and reproduction rates, the genes that caused the variation are passed down to the next generation. If environmental conditions do not change, the traits that provided increased survival and reproduction to the previous generation will also benefit the next generation. Over time, the trait is found in greater frequency in the population. (Microevolution) Over an even greater time various events can cause a single population to become so different that they can no longer reproduce with each other and produce fertile offspring. These organisms are no longer the same species. The events causing speciation are usually some type of reproductive isolation. Mutations and geographic isolation can also contribute.

Variations - Adaptations and Fitness Don’t confuse variations with adaptations! Variations are genetic and phenotypic differences within a species. They are owned by individual organisms. They may or may not be significant enough to provide an edge in survival and reproduction. Variations that can be inherited by subsequent generations that become standard phenotypical traits in a population become adaptations. Adaptations are inherited traits characteristic of entire populations that increases a population’s ability to thrive in a particular environment. Organisms with adaptations that increase the probability of survival and reproduction are said to be fit for their environment. They may be more or less fit than other organisms, and if the environment changes their degree of fitness can change!