5.4: Evolution Topic 5: Ecology & Evolution Miss Friedman

5.1: Definition Evolution is the cumulative change in the heritable characteristics of a population ► Darwinian Evolution is not simply based on natural selection but was in fact composed of at least five different “sub theories” 1. Evolution 2. Common descent 3. Gradualism 4. Multiplication of species 5. Natural selection

1. Evolution ► All life is and has been perpetually changing. This contrasts strongly with notions that all forms of life are constant and unchanging

2. Common descent ► All living things share a common ancestor if traced back far enough

3. Gradualism ► Evolutionary change takes place slowly and gradually. This contrasts with saltation in which changes are sudden and extreme

4. Multiplication of species ► Diversity of life is a consequence of speciation. Populations adapting to locations and becoming reproductively isolated from other populations

5. Natural selection ► A two stage process in which:  Producing genetic variation  selection

5.4.2: Evidence of evolution ► Evolution, like any scientific theory, requires evidence. ► Evidence shows that organisms change over time and even result in the production of new species of organisms ► Types of evidence 1. Fossil record 2. Homologous structures

1. Fossil Record A fossil is the ancient preserved remains of an organism. The fossil can be dated from the age of the rock formation. ► Sequences of fossil show the gradual change of an organism over geological time ► Although the planet Earth has extensive ocenas for most of its existence, fish fossils have only been found in rocks for 500 million years (less than 15% of the Earth’s age) ► No top predators such as bears and orcas existed in the time of dinosaurs ► Very few organisms today have identical form today as hundreds of years ago

2. Homologous structures Similarities between anatomical structure which are similar in form and function but which are found in seeming dissimilar species. The classic example is the pentadactyl (penta=five) and (dacytl=fingers) limb of the vertebrate

a) Humerus b) Radius c) Ulna In each example the bones are modified and adapted to the locomotion of the animal The fact that the basic shape and position of the bones is similar suggest that they have a common ancestor In the whale there is no real need for the fingers as they can still swim without them, this could suggest common ancestry with the other five-fingered organisms

Divergence ► The pentadactyl limb structure shows adaptation and modification from a common limb (ancestor) structure Convergence ► Two organisms with different ancestors have a limb structure that fulfills the same function but has evolved from different origins. ► Examples are wing of a bird and the wing of an insect

Selective Breeding ► Man has selectively bred animals and plants for thousands of years. ► If an animal posses a characteristic that is considered useful or valuable then this animal is selected for breeding. ► The hope then is that this characteristic will be present in the next generation and at a higher frequency than before. ► In subsequent generations it may even then be possible to select from an even more advantageous characteristic

Selective breeding continued ► The observations of artificial selection (selective breeding) suggested that natural populations would:  Show phenotypic variation  Be subject to natural selection pressures  There would be selection of those individuals possessing the advantageous characteristic

5.4.3: Population size & evolution ► The population produces more offspring than the carrying capacity of the environment can support:  Offspring/population compete for limited resources (Intraspecific competition)  Some individuals have characteristic (or combination) that gives them a competitve advantage  These individuals are more likely to successfully reproduce (offspring survive)  Through inheritance the frequency of these characteristics become greater in the next generation  By definition these characteristics have a genetic basis

5.4.4: Population size & survival ► Plant and animals produce far more offspring then could ever survive  Fish will lay hundreds of eggs yet only a handful survive ► Why are animal’s valuable resources wasted if they are never going to give offspring? ► Competition is set up for resources so only the best adapted organism will survive

5.4.4 continued ► It should be noted that the “struggle for survival” in this model is a consequence of over-population ► The struggle takes the form of individuals in the population being “selected for” or “selected against” ► Survivors form the new breeding population ► The frequency of advantageous alleles has increased ► The change in the heritable characteristics is by definition evolution

5.4.5: Variation in a species ► Populations of a species show variation ► Variation means differences in phenotypes ► Notice that no two humans are alike (or other animals)

5.4.6: Sexual reproduction & variation ► Asexual (bacteria) and sexual populations both experience mutation which increases the variation within the members of a population ► Sexual reproduction increases variation by the selection of mate or mutation  A fish with a better shaped mouth might be able to feed on coral that cannot be accessed by other fish, he will have a better chance of survival into adulthood  A fish mouth could be inadequately adapted and as a result die of starvation

5.4.6 continued ► Sexually reproducing populations also experience significant additional sources of variation ► There are two sources of genetic variation in populations: 1. Meiosis 2. Fertilization

1. Meiosis ► When is an egg is made during meiosis, only 50% of the mother’s information is needed. ► Due to random distribution of the chromosomes during meiosis, each egg has a different combination and therefore two eggs are never alike

2. Random fertilization ► Increases the variation in the population a second time ► Of the many sperm cells that exist, only one will fertilize the egg

Conclusion ► Genes get mixed up as a double lottery once in meiosis and a second time in fertilization

“… can we doubt (remembering that many more individuals are born than can possible survive) that individuals having any advantage, however slight, over others, would have the best chance of surviving and procreating their kind? On the other hand, we may feel sure that any variation in the least injurious would be rigidly destroyed. This preservation of favourable variations and the rejection of injurious varations, I call Natural Selection” Darwin C. (1859) The Origin of Species

5.4.7: Natural selection Natural selection is a two stage process: 1. Production of variation 2. Selection

5.4.7 continued ► When a population evolves there is a cumulative change in the heritable characteristics of the population ► Natural selection can act on a population without speciation occurring ► In effect the genetic profile of the population is adapting to changes in local conditions ► Ever phase in the process of evolution is affected by variation and by selection

Factors in a Model of Natural Selection

5.4.8: Examples of evolution 1, Antibiotic resistance in bacteria 2. Peppered Moth 3. New Zealand Kaka

1. Antibiotic resistance in bacteria