Topic 5: Ecology and Evolution 5.4: Evolution

Evolution slider The Big Bang The Simpsons

Earth’s evolutionary past: Life from more than 500 million years ago was greatly different from life today. Fish fossils have only been found in rocks 500 million years old or younger. (less than 15% of history of life) None of todays top predators existed at the time of dinosaurs or before. Few organisms today have identical forms in the fossil record. (Exceptions: cockroaches, ferns, certain sharks)

Charles Darwin “……can we doubt (remembering that many more individuals are born than can possibly 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 lease injurious would be rigidly destroyed. This preservation of favourable variations and the rejection of injurious variations, I call NATURAL SELECTION.” – On the Origin of Species Attenborough on Darwin

How Fossils Form Organism dies and gets buried. as layers of sediment are added, pressure increases, causing the sediments to compact into rock. As body decays, minerals seep into the it, filling spaces where gases or fluids used to be — this is known as permineralization.mineralspermineralization Alternately, the minerals in it chemically break down and are reformed or replaced. Eventually, most or all of what is left is a rock-like copy of the body. Sometimes, organisms are preserved in substances such as amber, ice or tar, as well. Occasionally, imprints get filled with sediments that harden into rock, creating natural molds or casts. A good example is animal footprints

Evidence for Evolution: fossil record Life 500 million years ago was very different from life today Fish fossils only date back to 500 million years ago or younger. (< 15% of history of life) None of the top predators today existed at the time of the dinosaurs or before Other than some sharks, cockroaches and ferns, most living organisms have no identical form in fossil record

Whales in the desert Whale evolution:

Heike’s crabs 4&feature=related

Homologous structures *Structures which are similar in form and function but are found in dissimilar species. Example: pentadactyl limbs are five- fingered limbs which differ in shape, number of bones and function. *Evidence for a common ancestor. – different uses, but basic shape and placement are the same

Homologous Structures

Evolutionary Mechanisms 1. Population produces more offspring than the environment can support. Utilize nutrients/energy of parents Force competition: food, mates, space Disease, predation, parasitism Leads to adaptive behaviors Ex. Cuckoo bird Ex. Flowers & insects 2. Variation Sexual Reproduction

Competition for food finding catching opening digesting Predation catching fighting avoiding escaping Parasitism invading avoiding removing tolerating Disease invading avoiding removing tolerating Competition for mates attracting fighting fertilising providing for Competition for spaces living space/shelter nesting reproductive space

Variation & survival Examples Camouflage Shapes of body parts such as beaks Mating preferences

Causes of variety 1. DNA mutation May produce disease May produce advantage Each generation only a few mutations. Most are not useful or harmful. Result is a wide array of variation

as a result of Random MutationSexual Reproduction DNA Replication Viral infection MeiosisRandom fertilisation Random assortment of chromosomes metaphase 1 Crossing over (recombination) prophase I

Evolution lab

Natural Selection When too many individuals exist for limited resources, survival is determined by surroundings & compatibility of characteristics w/ surroundings.

Natural Selection Steps 1. Over production of offspring w/ variation Useful increase/harmful decrease survival chance 2. Genetic characteristics poorly adapted to environment - Less successful at accessing resources 3. Genetic characteristics well adapted to environment – more successful at surviving

Steps cont. 4. Organisms that survive to adulthood more likely to reproduce & pass on successful characteristics 5. Over many generations, accumulation of heritable changes results in evolution. Gene pool has changed.

Antibiotic resistance in bacteria Staphylococcus aureus - bacteria Variation: MRSA – Methycillin-resistant MSSA – Methycillin susceptible Environmental change: application of methycillin Result: MSSA is killed MRSA survives & reproduces MRSA population increases, dominant strain Methycillin no longer effective against infection

Bacteria can continue to change and become resistant to all antibiotics – superbacteria Bacteria reproduce asexually. Little variation. Sources: mutation, plasmid transfer.

Pesticide resistance Variation: Most individuals are susceptible to pesticide. Some carry a gene for resistance Environmental change: pesticide sprayed Result: Susceptible population reduced. Resistant population survives and reproduces Gene for resistance increases in frequency Resistant population dominates Examples: resistance of malaria to DDT, Rats to poison

Not artificial selection: Humans are responsible for environmental changes- creating environmental changes – pressure organism to adapt or parish. *adaptations not “chosen” – results of environmental conditions. *solution at individual level- significant to a specific population

Other examples of evolution in action include resistance to pesticidesresistance to pesticides