5_evolution

Introduction to Evolution

**What is evolution?**
===** Evolution is a process that results in heritable changes in a population spread over many generations. ** === ===** Biological evolution is change in the properties of populations of organisms that transcend the lifetime of a single individual. ** ===

** Changes must be passed on to the next generation- heritable **
===** Therefore it can also be defined as:  any change in the frequency of alleles within a gene pool from one generation to the next ** ===

Theory of Evolution - microevolution - mechanism of evolution - evidence? **Video Questions** ** Does theory becomes a fact? Why is Evolution an important theory in Biology? What is the key element of hypothesis or theory? So what does a theory do? ** Theories explain facts - help us to understand Framework for asking questions in reality Big questions Leads to predictions Difference between HYPOTHESIS and THEORY - hypothesis is a guess, theory has certain evidence like a concept. Put together observations and inferences (conclusion drawn from evidence) - important part of science Scientific idea expressed through the effects of the theory - we cannot exactly see gravity, we can only see its effects
 * CONCEPT - ORIGIN OF LIFE**

- Explains Biodiversity - Macroconcept : CHANGE - over time - All species on Earth through a process of development - Process that results in **heritable changes** in a population spread over many generations - Change of properties of populations of organisms that transcend the lifetime of a single individual - Biological evolution refers to populations and not to individuals Defined as: any change in the frequency of alleles (type of gene - trait) within a gene pool from one generation to the next 23 chromosome pairs Male - XY (variety - X and X, female child, Y and Y, male child) Female - XX Reproduction Genetics in Sec 4 - how the genes are passed
 * Evolution**

Created by Charles Darwin, also discovered by Russel Wallace (with the help of many scientists)
 * History of Evolution**

- Realisation that organisms are not fixed and unchangeable - to provide an explanation for the mechanism - All organisms are modified descendent of previously existing forms of life - e.g. 13 different species of finches within different islands of the Galapagos - each with different type of beak for different functions An ancestral stock had migrated to the islands where they underwent profound changes under the different conditions of the individual islands -> different variety of species based on their needs (every beak has a form that serves its function) __Observations:__ 1. Populations have the potential to increase exponentially 2. Populations are fairly constant in size (stabilise) 3. Natural resources are limited (Food, space, water, shelter) 4. There is variation within a species and variation is inherited __Deductions:__ 1. Only Some organisms can survive. There is a struggle for existence among individuals in a population (O1, O2, O3) 2. Individuals with favourable variations are more likely to survive and reproduce (D1, O4) 3. Accumulation of variation over many generations is evolution (D2)
 * What did Charles Darwin observe?**

Adapted to conditions - build up of change over time, caused by ENVIRONMENTAL PRESSURE Useful characteristics survive and passed on to next generation e.g. dark colours to hide from predators __Factors:__ - Genetic variation - Overproduction of offspring - Struggle for existence - Differential survival and reproduction __Explanation:__ e.g. hummingbird characteristic - how efficient they are in getting nectar, wing shape, length/shape of bill The birds with the traits that help in that environment will tend to be passed on, hence after time, most of the population becomes adapted with the trait (population shaped by natural selection) Variations (genes - DNA) in a population caused by meiosis, mutation, cross fertilization, environmental influences etc. - Based on inheritance, not needs or intent - arose from random events - get passed down to next generation Overproduction of offsprings - organisms produce more young than needed (and able to survive) Struggle for limited resources (space, mate, basic needs etc.) Differential reproduction - favour individuals with advantageous traits - Will determine the composition of the gene pool Natural Selection occurs over a LONG period of time and results in EVOLUTION __Types of selection__ - Stabilizing selection Established adaptive phenotype are retained in greater numbers (middle range) - Directional selection gradually changing conditions, where the adaptive phenotype is shifter in one direction and one aspect of that trait is emphasized (one side eliminated) - Disruptive/Diversifying selection Favours two extremes of a trait (fluctuating environment), middle section eliminated
 * Change of characteristic - Natural Selection**

Larmack's hypothesis about adaptation of giraffes - WRONG - based on the need for certain features to be developed in order to survive, over generations passed down, differences develop to form a new species vs. Darwin - variations of inheritable features which already normally exist, environment screens out features contributing to survival and eliminate others (offspring have favourable traits) -> new species

Adaptation and Fitness - any HERITABLE trait that suits and organism to its function in its niche - it may be structural, physiological or behavioural - genetive adaptation has to be functional in the organisms natural habitat - it is not ACCLIMATIZATION which is an organism's ability to adapt during its lifetime to changing environmental conditions acclimatization - not heritable Fitness is a measure of how well suited an organism is to survive in its habitat and its ability to maximize numbers of offspring to reproductive age - Survival - Fecundity - Mating success

Industrial Melanism - where natural selection pressures due to man-made influences have led to colour changes in certain species e.g. tree colours change - moth colours change (selection shift of dominant gene) Modern Evolution - world of evolution of bacteria and viruses in humans e.g. Tuberculosis - drug-resistant resistant ones continue to survive and pass down, soon all the bacteria become resistant

(Online itunes lectures - scientific discovery at Cambridge)

Enduring Understanding of Evolution

 * 1) **Populations** of organisms changes across time.
 * 2) Evolution is a **series of changes**, some gradual and some sporadic, that account for the present form and function of organisms and systems.
 * 3) A community is a composite of populations in which individuals contribute to a gene pool that can change over time as a result of natural or artificial events.
 * 4) Evolution is the scientific explanation for the diversity of life on earth.