BIOE 103 Evolution
Review Galapagos Islands: birds similar to S. America Cape Verde Islands: birds similar to Africa 2
Our question for today: How do species change? Darwin figured out how. Charles Darwin 1809-1882
Lecture outline 1. Selective breeding 2. Natural selection 3. Requirements for natural selection 4. Definitions 5. An example 6. Origin of variation 7. Avoiding misunderstanding 4
1. Darwin argued evolution was caused by a natural process similar to plant and animal breeding. Charles Darwin 1809-1882
Selective Breeding example #1 All dog are descended from wolves* and have been bred by people into existing breeds Thousands of years later *Or an extinct wolf-like animal
Selective breeding example #2 Modern corn is much larger than corn raised by Native Americans Hundreds of years later 7
Evolution in nature is similar to this So we are going to examine how this occurs in some detail 8
Basic biology information you need to understand natural selection The physical characteristics of any living organism are affected by its genes and by its environment. Examples: Height -Height affected by genes - This is why tall parents tend to have tall children - Height is also affected by nutrition -This is why people in well-fed countries tend to be taller than people in less well-fed countries 9
Examples of genes and environment (in humans) Trait Genes or environment? Skin color Both genes and environment Native language All environment Number of fingers All genes (excepting accidents) Athletic performance Both genes and environment Academic performance Both genes and environment 10
Wolves are larger, have thicker fur, different shape, bigger teeth, etc. than Chihuahuas because they have different genes.
Modern corn is genetically different than native corn 12
These are genetic transformations 13
How would you do this? Please give me step-by-step instructions for doing this that you conceivably do yourself. (E.g., Don t tell me you are going to use genetic engineering) 14
How to turn a wolf into a Chihuahua 1. Start with a population of wolves that have varying sizes and shapes. 2. Select the wolves that are smallest, or look at least a little like a Chiuahua. 3. Breed these Chihuahua-like dogs. 4. These dogs have Chihuahualike puppies 5. Continue until you have a Chihuahua.
When you select short wolves to breed, you are selecting individuals with certain genes Wolves Small dogs TTCTGTTCGCCAGCCGGGCCCTGGCAAGCTGAGAC...A... For example, chihuahuas and other miniature dog breeds have a different version of the gene insulin-like growth factor I receptor. Selectively breeding small dogs will increase frequency of the gene sequence having an A (above) in population. Remove G s. 16
Examples of selective breeding Wild jungle fowl Lay 30 eggs / year Domestic hen Lays 300 eggs / year
Examples of selective breeding Broccoli, cabbage, kale, cauliflower, kohirabi all bred from wild mustard
Selective breeding can change almost any trait in any organism E.g. Colors in carrots See Selective breeding
2. Natural selection causes evolution in a similar way (except nature selects who reproduces) 20
Alaskan winter breeds musk ox to have warm wool Some oxen have warmer wool than others. Musk ox without warm wool do not survive to reproduce. Offspring of surviving musk ox inherit warm wool. This changes the population of musk ox.
Mountains breed sheep to be surefooted Sheep that are not surefooted do not survive to reproduce
Cheetahs breed dik diks to be fast Cheetah s don t want dik diks to be fast. But cheetahs eat the slow dik diks, so only the fast dik diks survive to reproduce.
Desert climate breeds cactus to conserve water Desert animals breed cacti to have spines
3. Requirements for natural selection Hypothetical case study: Giraffes feeding from acacia trees
During a drought, there is a food shortage
The shortest giraffes die
Surviving (tall) giraffes have tall calves
And the average height of the population has increased
Requirements for natural selection 1. Variable trait 2. Trait is heritable (genetically based) 3. Differential survival/reproduction ( selection )
If these three conditions are met, a population WILL evolve If these conditions are NOT met, a population will NOT evolve.
Natural selection practice problem The giant anteater of South America eats only ants and termites. Anteaters eat ants by sticking their tongue into anthills and slurping up ants. Anteaters have an elongated snout and their tongue is two feet long. According to the theory of evolution, anteaters evolved from animals that did not have such a long tongue. How would an evolutionary biologist explain how this change occurred? 32
Answer: There was variation in the ancestral population of anteaters; some of the ancestral anteaters had longer tongues than others. The anteaters with longer tongues were more likely to survive and reproduce than anteaters with shorter tongues. The surviving anteaters had offspring that inherited the long tongue. 33
Natural selection practice problem Sequoia trees live in mountains in California where forest fires are common. Sequoia trees have very thick bark that protects them from forest fires. According to the theory of evolution, sequoias evolved this thick bark from ancestors that did not have it. How would an evolutionary biologist explain how this change occurred? 34
Natural selection practice problem Whales are large mammals with streamlined bodies that allow them to swim easily in the ocean. Unlike most mammals, whales do not have hind limbs. How would a biologist explain how whales lost their hind limbs, assuming their ancestors had hind limbs? 35
4. Definitions selection An environmental influence that gives some individuals in a population a reproductive or survival advantage over others. Principal cause of evolution. 36
Evolution: 2 definitions 1. The theory that all species are descended from a common ancestor, and have changed with time 2. A change in genetic composition of a population. 37
This population has different genes after the drought. Therefore it has evolved.
Evolving in everyday speech means something different than in biology Evolve (everyday speech) : To undergo gradual change; develop Britney had to evolve since the music industry How did Ford evolve from one of the most admired companies people need to evolve with the changing markets Lance Armstrong s brand is evolving
5. An example of evolution in nature: Beak depth in Darwin s Finch in Galapagos Islands Beak depth 40
Finches with wide beaks are better at cracking open large seeds. Finches with narrow beaks are better at eating small seeds. 41
Beak depth is a genetic trait Parents with deep beaks have offspring with deep beaks 42
Bill depth in Darwin s finches before and after a drought makes small seeds scarce 80 N 60 40 Before drought Avg = 9.59mm 20 0 7 8 9 10 11 12 13 80 60 N 40 20 After drought Avg = 10.09 mm 0 7 8 9 10 11 12 13 Beak depth 43
This may seem like a trivial change but changes like this can transform a species if they keep occurring over a long time. (Similar to plate tectonics). 44
6. Origin of new variation Natural selection changes proportions of individuals in a population. It won t work unless there are some tall individuals. So where do the tall giraffes come from in the first place? 45
Mutation creates individuals with new traits This giraffe has a mutation that makes it taller. Mutations are random changes in genes. Mutations are caused by mistakes copying genes when cells reproduce or by the effect of radiation or chemicals. Random means mutations happen by chance not because they are needed. Most mutations are harmful; but some are beneficial.
7. Avoiding common misunderstandings Evolution does not happen through a process similar to sun tanning in which individuals change. Getting a sun tan may darken your skin, but it will not change your genes (and therefore does not affect your children). 47
Shivering doesn t change genes of individual musk ox. Evolution occurs when environment changes genes in a population by selecting who survives and who reproduces.
Giraffes didn t evolve long necks by stretching to reach branches Stretching may lengthen a giraffe s neck, but will not change a giraffe s genes. This change will not be inherited. 49
Species don t evolve just because they need to All of the finches needed larger beaks, but that didn t cause any finch to change. Finches with narrow beaks died. 50
The key to understanding natural selection is applying these requirements Be ready for exam questions that test whether you can do this. 51
Quiz Wednesday on Natural selection 52
Study guide Be able to explain the difference between evolution and natural selection. Be able to define evolution in two ways. Learn the requirements for natural selection. Be able to use the requirements for natural selection to describe how evolution occurs (see cheetah evolution sample question ) 53
Sample exam questions Cheetahs are able to run faster than 60 miles per hour when chasing prey. How would a biologist explain how the ability to run fast evolved in cheetahs, assuming their ancestors could run only 20 miles per hour? Bowhead whales are the only species of the great whales that live their entire life in the cold water of the Arctic Ocean. Bowhead whales have a thick layer of fat called blubber that helps keeps them warm in the cold water they live in. According to the theory of evolution, bowhead whales evolved their thick blubber from ancestors whose blubber was not as thick. How would an evolutionary biologist explain how this change occurred? 54
The end 55