Evolution, Natural Selection, Cladograms and Evidence of Evolution

Evolution Evolution is change within a population over time. Charles Darwin (a scientist and a naturalist) proposed the theory that evolution happens by NATURAL SELECTION – populations CHANGE over time in response to changes in the environment.

Natural Selection What does natural selection mean? The environment changes and acts on variations (differences in characteristics – controlled/ determined by genes) within populations – only those individuals with the “best” variations (the best genes) for the new environment survive and pass on their genes. Over many generations, more and more of the members of the population have these genes/ characteristics. These characteristics are called favorable variations, or ADAPTATIONS! What are adaptations? Adaptations are characteristics that increase an organism’s chances of surviving and reproducing in their environment.

Methods of Evolution Evolution can create new species (speciation), and it can happen quickly or slowly Gradualism – small changes in the environment lead to small changes in populations over LONG periods of time (population changes SLOWLY) Punctuated Equilibrium – Fast/ large-scale changes in the environment cause one species to become two (or more) different species (they can no longer reproduce)

Natural Selection and Artificial Selection Natural selection/ breeding: Individuals within populations mate on their own, with NO external (human) influence and are subject to natural selection Artificial selection/ breeding: Individuals within populations are forced to mate/ reproduce with others in the population by humans Why artificial breeding? Better/ healthier crops and/ or livestock More desirable traits (dogs, horses, flowers etc.) Why not artificially breed? It decreases genetic variation – there are not as many differences in the gene pool (the total number of genes from every individual in a population) so the population is more fragile (vulnerable/ susceptible) to changes in environment

Peppered Moths Industrial melanism is the darkening of populations over time in response to pollution in the environment. Peppered moths have TWO color variations – light and dark (two different alleles) Around the 1850’s (the industrial revolution) the darker moths became more frequent in the forests around industrial centers. WHY?

How do scientists show how different species are connected? A cladogram is a branched diagram which shows how organisms are related. At each branch, or "Y”, characteristics of evolutionary origin are used to separate one group from another.

Cladograms can also be used for organisms very closely related

Comparing organisms Which are more similar: a rabbit and a crocodile or a bird and a crocodile. Explain your answer including specific traits.

What evidence supports the Theory of Evolution? Molecular Evidence (DNA) Scientists can analyze DNA from different organisms. The more similar the DNA, the more closely related they are! Biogeography The study of the distribution (where they are found) of species. Organisms in places that are near each other will be more similar/ closely related. When land masses separate (islands, continental drift etc.) species will evolve differently to “fit” the different environments, and eventually become different species (no longer able to reproduce). They are still similar, though, because they share a common ancestor.

Comparative Embryology An embryo is an unborn organism in the earliest stages of life. The embryos of very different organisms are very similar, suggesting that the basic body plan of organisms is formed based on similar DNA instructions that came from a common ancestor. Example: Fish embryos and human embryos both have gill slits! Comparative Anatomy Similar body structures are found in different organisms. They are “built/ put together” with the same basic parts. This shows “variation on a theme.” A similar, basic body plan has adapted to “fit” different environments. Example: forelimbs (bat wings, whale front fins, human arms, dolphin fins, horse forelimbs, cat forelimbs)

The Fossil Record Artificial Selection/ Breeding Fossils are the remains of once-living organisms. They show that once-living organisms were similar to those living today (those fossils in younger rocks) or very different (those fossils found in older rocks).   Artificial Selection/ Breeding Humans can choose/ select which organisms to mate. Over many generations, the genes in these domesticated populations are very different than their wild counterparts. This shows that the gene pool CAN change over time due to selection (even though it is artificial selection).

Evidence for Evolution Video (Paul Anderson) http://www.youtube.com/watch?v=cC8k2Sb1oQ8&safety_mode=true&persist_safety_mode=1&safe=active