Adaptations and Natural Selection
How Natural Selection, Genetic Variation, and the Environment Influence Evolution Charles Darwins theory of evolution (the idea that organisms change through time) challenged prevailing 19th-century notions of a static world. Previous explanations all linked to theology. - Christianitys Great Chain of Being Organisms were seen as IMMUTABLE (unaltered since creation). Assumed a very young Earth that was formed < 10,000 years ago. Catastrophes (e.g. the Noachian Deluge) explained the extinct organisms found in the fossil record. Darwins voyage aboard HMS Beagle.
trip around the world. Set out to document the hand of God in nature. Collected countless specimens and kept detailed notes. Darwin saw many things that were difficult to reconcile with the prevailing view of a young Earth and the immutability life. Blue-footed Booby (Sula nebouxii) Finches of the Galapagos Islands Returning home, Darwin married and moved to a country home.
For the next 20 years, he published books about his findings on the Beagle and worked quietly on the species problem. Darwin knew about artificial selection, and argued that a similar process must occur in nature.
Wild mustard & domestic cruciform vegetables Domestic dogs Wild canids This led him to the idea of natural selection.
Natural selection rests on three indisputable facts: Organisms produce more offspring than can survive. Individuals vary in their characteristics. Many characteristics are inherited by offspring from their parents. It follows logically that
Some individuals will be better suited to their environment - they will survive and reproduce more successfully than individuals without those characteristics. Future generations will thus contain more genes from better-suited individuals. As a result, characteristics will evolve over time to resemble those of the better-suited ancestors. Phylogeny of the Galapagos Finches Fitness is the likelihood that an individual will reproduce and/or the number of offspring an individual produces over its lifetime. Adaptive trait or adaptation is a trait that increases an individuals fitness. Natural selection or survival of the fittest states that individuals that are better suited to the environment (the best adaptations) survive and reproduce more successfully. Gypsy Moths in England industrial revolution - coal and other industrial factories spewed out massive amounts of air pollutants The original color of the gypsy moths was a light gray; Tree trunks were darker colored from the air pollution. The dark gray gypsy, once at a disadvantage and quickly eaten by predators, now survived and bred, while their lighter counterparts were eaten. The gypsy moths didn't just decide one day to change their color, at the basis of such a change was the concept of Natural Selection. The development of pesticide resistance in insects is another example of real-time evolutionary change. Natural selection is also responsible for: antibiotic resistance in bacteria herbicide resistance of weeds HIV resistance to anti- retroviral drugs Examples of Adaptations 1. Camouflage (Cryptic) 2
Examples of Adaptations 1. Camouflage (Cryptic) 2. Disruptive Markings 3. Warning Coloration 3. Mating Coloration 5. Batesian Mimicry MullerianMimicry 7. Automimicry Camouflage Cryptic: Concealing form and coloration which enables a species to avoid its natural predators by camouflage. Two examples of camouflage in San Diego County: A canyon tree frog (Hyla californiae) on canyon wall (left) and a desert horned lizard (Phrynosoma platyrhinos) on a sandy riverbed Camouflage These two katydids sitting on a tomato plant are well camouflaged. Note the veins in the wings that resemble leaves. Disruptive Markings Disruptive Markings: The markings on some insects, reptiles and mammals make it difficult to distinguish them from shadows and branches or from other members clustered together. The stripes on a zebra may appear quite distinctive, but to a colorblind lioness it is difficult to single out an individual zebra among a dense population in the African grasslands. Warning Coloration Warning Coloration: Insects with an obnoxious quality (at least to would-be predators), such as bad taste, bad smell or powerful sting, often exhibit bright colors to warn of their presence. Warning coloration is well developed some insect, including bees and wasps. Small poison dart frogs of the tropical rain forest also exhibit warning coloration. These frogs contain very toxins in their skin Mating Coloration Mating Coloration: Bright colorations among the males of some animals (particularly the plumage of birds) gives the male a definite advantage in sexual selection and mate attraction. Mating coloration and behavior of the most "fit" and aggressive males serves to stabilize the population density because only the most sexually select males are able to mate with females of the species. Batesian Mimicry Mimicry: One insect (called a mimic) that is perfectly palatable to its predator resembles another insect (called the model) that is quite disagreeable to the same predator. There are actually two types of mimicry: Mimicry in which the mimic is essentially defenseless is called Batesian Mimicry. One of these insects is a stinging honeybee and the other is a harmless fly that mimics the bee. Although the fly cannot sting, it greatly resembles the bee. Because of this remarkable resemblance, some of the fly's predators tend to leave it alone Mullerian Mimicry Mimicry in which the mimic shares the same defensive mechanism as the model is called Mullerian mimicry. The yellow jacket wasp and bumblebee (Bombus) are Mullerian mimics because they both have bright yellow and black colors and use powerful stings as a defensive mechanism. Automimicry In automimicry, an animal mimics parts of its own body. For example, some snakes have a tail that resembles their head and a head that resemble their tail. A predatory bird swooping down on its prey might miss its capture when the prey suddenly moves in an unexpected (backwards) direction. Automimicry is well developed in Malaysian lanternflies of the large insect order Homoptera