Individuals do not evolve, populations do IB Topic 5.4: Evolution Individuals do not evolve, populations do

What is evolution? Evolution Cumulative change in the heritable characteristics of a population Change over time Simpson’s couch gag http://www.jibjab.com/view/131239

What’s the evidence for evolution? Charles Darwin Contributed more to our understanding of evolution than anyone else Born 1809 Traveled on the H.M.S. Beagle In 1831 set sail (at the age of 22!) from England for a voyage around the world Made numerous observations and collected evidence that led him to propose a radical and revolutionary hypothesis about how life changes over time Evolution Evidence: fossil record, artificial selection, homologous structures

The Fossil Record Life 500 million years ago is very different from life today Fish fossils have only been found in rocks ~500 millions years old or younger (less than 15% of the history of life) Top predators today did not exist at the time of dinosaurs (or before) Many living organisms today have no identical form in the fossil record Conclusion: life on Earth is constantly changing

Artificial Selection Breeding domesticated animals Breeders choose the males and females with the most desirable genetic characteristics and breed them together Examples? Conclusion: Evidence that evolution is happening, but the driving force is human choice Not the driving force of evolution in natural ecosystems

Homologous Structures Similar in form and function, but found in dissimilar species Example: 5 fingered limb Humans, whales, and bats (see fig. 5.8 page 147) Humerus, radius, ulna, carpals Pentadactyl (penta – 5; dactyl – fingers) The shape and number of bones may vary, but the general format is the same Conclusion: evidence that the organisms in question have a common ancestor

Struggle for existence Organisms produce many more offspring than survive to be mature individuals Darwin did not coin the term ‘struggle for existence’ but it does sum up the point that over-production of offspring in the wild leads to their competition for resources

No. of eggs/seeds/young per brood or season Some examples Organism No. of eggs/seeds/young per brood or season Rabbit 8-12 Great tit 10 Cod 2-20 million Honey bee (queen) 120,000 Poppy 6,000 Many of these offspring die before they reproduce

Darwin’s Observations 1st Observation Populations tend to reproduce rapidly and if every individual survived, there would be exponential growth Not the case Seems to be a natural checks and balance system There is a limit to the size of a population that the environment can support Deduction There is a struggle for existence Some live and some die

Darwin’s Observations 2nd Observation Organisms vary There are differences between individuals of the same specie These differences affect how well suited an organism is to its environment (fit or fitness) This is called adaptation Some individuals are better adapted to their environment than others because they have favorable variations Deduction In the struggle for existence, the less well-adapted individuals will tend to die Natural selection

Darwin’s observations 3rd Observation Much of the variation between offspring can be passed on to offspring It is heritable Deduction Better adapted individuals reproduce & pass on their favorable characteristics Over the generations the characteristics of the population gradually change Evolution by natural selection

Why do individuals within a specie show variation? Genetic variations arise from gamete formation and fertilization Random assortment Crossing over Random fusion of male and female gametes during sex Mutations Not as powerful as sexual reproduction Mutations by be advantageous, harmful, or neutral Most mutations are neither harmful or useful Does this sound familiar?

Evolution in Action Galapagos Finches Darwin visited the Galapagos Islands in 1835 and collected specimens of small birds (finches) Group of islands off the coast of Ecuador 14 species in all Darwin observed that the size and shapes of the beaks varied, as did their diet Further research from Peter and Rosemary Grant suggests a close relation between beak characteristic and diet

Examples of natural selection Antibiotic resistance in bacteria Pesticide resistance in rats

Antibiotic resistance in bacteria: more evidence for evolution Antibiotics were one of the great triumphs of medicine in the 20th century When they were first introduced, it was expected that they would offer a permanent method of controlling bacterial diseases However, there have been increasing problems of antibiotic resistance in pathogenic bacteria.

The following trends have been established: After an antibiotic is introduced and used on patients, bacteria showing resistance appear within a few years Resistance spreads to more and more species of bacteria Strains of bacteria appear that are resistant to more and more different antibiotics Called multiple resistance

How? Antibiotic resistance is due to genes in bacteria and so it can be inherited Example of evolution by natural selection The evolution of multiple resistance has occurred in just a few decades. It is so important to finish all of your prescribed antibiotics Due to: Widespread use of antibiotics (humans and animals) Bacteria reproduce quickly (less than 1 hour) Populations of bacteria are HUGE, increasing the chance of a gene for resistance to form via a mutation If you want more info: http://www.fda.gov/oc/opacom/hottopics/anti_resist.html

Pesticide resistance in rats What are pesticides? Typically used by farmers Due to natural variation, some rats are unaffected (resistant) to the toxin They survive and reproduce, making a new population in which some or all members possess the genetic resistance New pesticide must be used The cycle continues …

Take away … Illustrates how a population can adapt to its environment Illustrates how humans can be responsible for creating “super-resistant creatures” Why is this not an example of artificial selection?

Flanders calls Homer an ape and makes a case for evolution revolution in THE SIMPSONS episode "The Monkey Suit"

Exit Slip 3 multiple choice questions 1 minute to answer each question before screen changes.

Question1 What is natural selection? The mechanism that increases the chance of certain individuals reproducing. The mechanism that leads to increasing variation within a population. The cumulative change in the heritable characteristics of a population. D. The mechanism that explains why populations produce more offspring than the environment can support.

Question 2 Which factors promote evolution in a species? I. Sexual reproduction II. Environmental change Overproduction of offspring A. I and II only B. II and III only C. I and III only D. I, II and III

Question 3 Natural selection is based on which of the following? I. Variation exists within populations. II. There is differential reproductive success within populations. Individuals must adapt to their environment. A. I only B. I and II only C. II and III only D. I, II and III