Evolution by Natural Selection 15-1 & 15-2

What is Evolution? = A change in a species over time = A change in a population over time (micro) Examples: Drug resistant bacteria Snails with different shell thicknesses = A change in the community over time (macro) Dinosaurs replaced by what we see today

Mechanisms of change How did/do these changes come about? What mechanisms are responsible for generating the diversity of species we observe? Science looks for mechanisms that can bring about the changes or diversity

Charles Darwin British Naturalist Hired as a naturalist to collect specimens on a voyage around the world Voyage on HMS Beagle in 1831

Darwin’s Voyage

What got Darwin thinking? Organisms seemed well suited to their environments – how? Species don’t always appear where you would expect based on habitat – why? Similar species located close to each other show slight differences in appearance – why? Galapagos Tortoise shells and neck lengths Wide diversity of beetles in Brazilian Rain Forest Fossils of previously unknown creatures

Galapagos Tortoises

Beetle Diversity

Darwin influenced by other scientists James Hutton & Charles Lyell: Earth is shaped by normal geologic forces over a long period of time. Alfred Wallace is also speculating about how species could be shaped by natural forces over time Domesticated animal breeds were shaped by breeding (artificial selection) Darwin publishes his idea in a book (1859): “On the Origin of Species…”

Lamarck’s idea

Lamarck’s ideas 1) Traits can be acquired from use or need 2) Traits can be lost through non-use or lack of need 3) Acquired traits can be passed on from parents to offspring Errors: 1) Acquired traits cannot be passed on because they have no genetic basis (DNA) 2) Traits are not likely to appear due to need or disappear from non-use

Name that breed! A game of great skill

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Artificial selection How are dog breeds created? 1) Find parents that display the traits you want 2) Let them mate and reproduce 3) Observe the offspring and select those you wish to breed in the future (traits) 4) Eventually some traits become very common and pronounced while other traits are eliminated

What is natural selection? = organisms that reproduce most successfully will pass on more traits to the next generation -Future populations will have the traits of the most successful reproducers from the previous generations -Think about the snails! -Organisms that are best adapted for survival in the environment will probably be the best reproducers -Not necessarily strongest & fastest -Why are male and female birds colored differently?

Red-winged Blackbird (R) Male Female

Male vs. Female Birds Males draw lots of attention to themselves to advertise for mates Bright colors, long, loud songs Singing from a prominent perch Females avoid attention so as not to advertise the presence of a nest Camo coloration Less vocal, short calls Stay secluded From an evolutionary standpoint, the males have developed traits that make them an easier target for predators but they result in better reproductive success.

Natural Selection – 3 conditions needed 1) Variability exists in a certain trait - new variations can come from immigrants or mutation

Natural Selection – 3 conditions needed 2) The trait must be heritable (not acquired) to be passed down HeritableAcquired

Natural Selection – 3 conditions needed 3) Selective Pressures in Environment lead to Differential Reproduction Differential reproduction = some individuals with one version of the trait produce more offspring than others with the other version Fitness = offspring an individual contributes to next generation A good trait that leads to better fitness = adaptation

Natural Selection – the result 4) Given enough time, the most advantageoustraits should become common in a population