CLASSIFICATION

CLASSIFYING THINGS All life is found within a layer around the Earth called the biosphere. The biosphere includes anywhere that life exists – including the land, water and air. It’s about 16km thick and accounts for very little of the planet’s actual mass. Biologists estimate that there are between 30 million to 100 million different species within the biosphere, yet, only 1.75 million have been identified and described. Early attempts at classification were based on the habitat of the organism or the type of material produced if the organism happened to be a plant. These systems had to be replaced as more and more organisms were discovered. Today we classify organisms according to species. A species is a group of organisms that share many physical & physiological traits and are capable of freely interbeeding (mating) and producing viable offspring.

Linnean Classification Swedish scientist Carolus Linnaeus is the father of the modern system of classification known as binomial nomenclature. This system involves each organism having a two-part name. The first name is the genus. The second name is the species name of the organism.

TAXONOMY The science of naming organisms and assigning them to these groups is called taxonomy. The categories that are used to classify living things are called taxa (singular = taxon). Taxonomy classifies organisms on several different levels. Starting with the broadest level and working down to the smallest level we have… KingdomAnimalia Phylum/DivisionChordata ClassMammalia OrderPrimates FamilyHominidae GenusHomo Speciessapiens

HAIL TO THE KINGDOM The first two kingdoms to be recognized were Animalia and Plantae. As technology advanced we soon discovered the kingdoms of Protista, Fungi and Monera. The kingdom monera – which are the bacteria – would later be split into the kingdoms Archaebacteria and Eubacteria. In your notes, list the six kingdoms used in classification and state the identifying factor(s) that are unique to each one.

DICHOTOMOUS KEYS These keys are used to help classify organisms based on their structural similarities or differences. The key works by asking a series of “yes or no” questions about the organisms – you chose either yes or no and then proceed to the next question that follows your answer. Eventually your answers lead you to an identification of the organism. Create a dichotomous key using several members of the class. (Remember, it is similar to playing the game “Guess Who”.)

PHYLOGENY Phylogeny is the evolutionary history of a species or group of species that share a common ancestor. We can make links between different species by examining their traits – both structural and molecular – and examining the similarities and differences. Evidence used when making phylogenetic connections… Embryology – The embryonic development between many seemingly “unrelated” species will show you that we all start out looking much the same and then diverge into the various forms you see in the adult stage of the organism. (Ontology Recapitulates Phylogeny)

PHYLOGENY Homologous Structures – These are structures that are similar in terms of physical structure but may have very different functions. If you examine the forelimb of the animals shown here, you will see that there are remarkable similarities in the bone arrangement and position within the limb. They would have gotten these structures from a similar ancestor – hence a historical connection.

PHYLOGENY Genetic Similarities – Many of the molecules that are used in the structures of organisms and the enzymes that facilitate important reactions in the body are very similar between species. If proteins are similar, they indicate similarities in the genetic code. (DNA  RNA  Protein) Using these similarities, we can establish a basic relationship between the physical forms of the various species and how closely they are related by a common ancestor. We show these relationships using a phylogenetic tree.

PHYLOGENETIC TREE

DIVERSITY & NATURAL SELECTION Why do we have so many different life-forms if we started out from one common ancestor? Environmental pressure…As organisms branch out and cover the planet, they experience a variety of different environmental conditions. The organism must have the traits needed to survive and reproduce in the environment or they may perish (nice way to say die). Different environments will value different physical traits – these physical differences become more emphasized over time. The result is a number of organisms that are different from one another – increased biodiversity.

DIVERSITY & NATURAL SELECTION According to the widely accepted theory of evolution by natural selection, the environment decides (selects) which organisms are going to be a good fit and which are not. The ones that fit well promote the next generation and those that don’t fit do not. This is the basic idea behind natural selection – it is survival of the fittest. The theory of natural selection is based on four observations… 1.All members of a species display a variety of characteristics in their appearance and behaviour – many of these are inherited variations. 2.The number of offspring produced by individuals in a species exceeds the number of offspring that will survive to adulthood. 3.Some offspring, because of their individual differences, are better able to adapt to the conditions of the environment than others. 4.The better-adapted organisms survive more often and will pass on their characteristics to their offspring and, as a result, the population changes. If none of the members of a species can adapt to the environment – the species will go extinct.

NATURAL SELECTION

ARTIFICIAL SELECTION Artificial selection occurs when humans chose the desired traits within a species and select which individuals shall be bred and give rise to the next generation. The humans select the fit individuals instead of the environment – hence the name artificial selection. The dogs below are the result of people choosing their traits – not nature.

Reproduction, Genetic Diversity & Species Survival Reproduction is used to produce the next generation of offspring in a population. A species may reproduce either asexually or sexually. Asexual reproduction involves only one parent organism and the offspring are genetically identical to the parent (clones) – there is little diversity within the population. Sexual reproduction involves two separate parents and uses gametes (sex cells) that are formed by the process of meiosis. During meiosis, an event known as crossing over occurs in which the chromosomes reshuffle the genes they carry and create new combinations. Random assortment also occurs which causes the offspring to have a mix of both maternal and paternal traits. When you calculate the number of possible genetic combinations available in a human, the number reaches roughly 14 trillion different genetic possibilities.

WHY IT’S GOOD TO BE DIFFERENT Genetic variation is important because of the environment’s ability to suddenly change. This change could be in terms of climatic change, introduction of toxin or disease or an increase in the number of predators. When you have great diversity within the species, you will have a better chance of one of the members of the species possessing the traits that will enable them to survive the environmental change and keep the species alive. As these survivors reproduce, more of the population will have the traits needed to survive as they were inherited from their parents.

THAT’S ALL I GOT…