Version: 2.0 Phylogeny

Phylogeny and Taxonomy The evolutionary history of a group of related species is called phylogeny. Reconstructing phylogenies involves identifying and classifying species to show their evolutionary relatedness: a scientific discipline (or area of study) called taxonomy.

The central idea of biological evolution is that all life on Earth shares a common ancestor, just as you and your cousins share a common grandmother. Through the process of descent with modification, the common ancestor of life on Earth gave rise to the fantastic diversity that we see documented in the fossil record and around us today. Evolution means that we're all distant cousins: humans and oak trees, hummingbirds and whales. Common Ancestors

Understanding phylogenies Understanding a phylogeny is a lot like reading a family tree. The root of the tree represents the ancestral lineage, and the tips of the branches represent the descendents of that ancestor. As you move from the root to the tips, you are moving forward in time.

When a lineage splits (speciation), it is represented as branching on a phylogeny. When a speciation event occurs, a single ancestral lineage gives rise to two or more daughter lineages.

Phylogenies trace patterns of shared ancestry between lineages. Each lineage has a part of its history that is unique to it alone and parts that are shared with other lineages.

Similarly, each lineage has ancestors that are unique to that lineage and ancestors that are shared with other lineages — common ancestors.common ancestors

Plate Tectonics and Continental drift Plate Tectonics The movement of the plates that make up the surface of the Earth that contributes to continental drift. Continental drift The crust of the Earth is in constant motion, moving whole continents and sea floors. The movement of continents, at times joining and at other times separating, has had a powerful effect on the distribution of organisms

Evolution by natural selection Darwin concluded that natural selection could explain how organisms gradually change and evolve into new species. At the time of publishing Darwin found it difficult to get his theory accepted, as it was difficult to prove. Other scientists at the time wanted Darwin to provide an explanation to how individuals passed on their characteristics to their offspring. Since Darwin’s time advances in our understanding of genetics have provided evidence to support and extend Darwin’s theory.

Evolution through natural selection involves: The consequence of this is what Darwin described in his book as a “struggle for existence”. The weakest are eliminated in this struggle. The fit survive. The survivors pass on their traits to their offspring. Over enough time, these differences in characteristics will lead to the formation of a new species

This is what Charles Darwin meant by Natural selection is the process of evolution- the mechanism which allows the organisms that are better adapted to survive in the environment in which they are living, to reproduce more successfully - thus spreading their genes throughout the population. What is Natural selection ? “ survival of the fittest ”

Natural selection works by tiny mutations (changes) in the genes that are always happening during sexual reproduction- when a mutation is beneficial to survival of the organism it eventually, generation after generation, becomes more dominant in the population, and a new species is formed. How does Natural Selection work?

Thus the ENVIRONMENT naturally selects those genes that increase the chances of survival to adulthood and therefore reproductive success. What determines natural selection?

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