8/21/2014. Most important concept of biology links the whole subject

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1 Chapter 22 Pg Definition: frequency of heritable traits changes from one generation to the next Includes changes in a population, species, or group of species Evolutionary change is based on the interactions between populations & their environment which results in adaptations (inherited characteristics) to increase fitness Most important concept of biology links the whole subject An allele is one of several (or many) varieties of a gene Individuals inherit alleles that code for traits that establish morphology (form/structure), physiology, or behavior Evolution is when the frequency of these alleles in the population changes over time Diplody: diploid eukaryotes (two sets of DNA, like YOU!) are capable of hiding genetic variation (recessive alleles) from selection Heterozygote advantage: some recessive genes, while disorder-causing, may be helpful in a way; heterozygotes have a dominant allele and recessive allele, and would benefit from the presence of each Example: sickle-cell disease homozygous normal individuals are more susceptible to malaria, and homozygous sickle-cell individuals suffer from complications of their disorder Aristotle ( BCE): Scala naturae life-forms can be arranged on a scale of increasing complexity Old Testament: perfect species were individually designed by God Grouped similar species into general categories reflecting what he considered the pattern of their creation (anatomy and morphology) Developed taxonomy the branch of biology dedicated to the naming and classification of all forms of life. Domain Kingdom Phylum Class Order Family Genus Species Domains: Eubacteria, Archaea, Eukarya Developed binomial nomenclature a two-part naming system that includes the organism s genus and species 1

2 Georges Cuvier ( ): French geologist and paleontologist, opposed evolution. Advocated catastrophism events in the past occurred suddenly and by different mechanisms than today (catastrophe destroyed many living species, then areas were repopulated by immigrant species). This explained boundaries between strata and location of different species. Hutton: described gradualism, the slow and subtle changes in organisms caused by slow and continuous geologic change Charles Lyell ( ): described uniformitarianism, the idea that Earth s processes have remained at the same rate through all of time, so Earth is very old. Malthus ( ): when more babies are born than deaths, war, famine, and disease are results of overcrowding. This causes a struggle for existence. One of the earliest advocates for evolution, and the first to support it by publishing his theories. They included: Evolution was a natural progression towards perfection, and organisms proceeded up a ladder of complexity. Use and disuse described how body parts can develop with increased usage, while unused parts weaken. This idea was correct (think athletes that train for competitions!). Inheritance of acquired characteristics described how body features acquired during the lifetime of an organism (like muscle bulk) could be passed on to offspring. This was incorrect only changes in genetic material can be passed on. Importance: Lamarck recognized that species evolve, though his explanatory mechanism was flawed. He developed ideas of adaptation and heritability. Published in 1809, Darwin s birth year. Darwin went to med school at 16, dropped out, and joined the clergy; he ended up on the HMS Beagle. He traveled to South America and the Galapagos Islands, collecting specimens of plants and animals, as well as fossils, and constantly made observations. 50 years after Lamarck published his ideas, Charles Darwin published On the Origin of Species His theory stated that natural selection, or survival of the fittest, was driving the force of evolution ( descent with modification ) South America: species were related but different from European species. Fossils didn t match European fossils, but S. American fossils were related to S. American species, implying some sort of descent. Galapagos Islands: west coast of S. America, different varieties of species were on each island, all of which were related to mainland S. American species. Darwin also noticed each island had unique finches that seemed perfectly suited to its own habitat. Reasoning: gradual accumulation of adaptations to an environment could lead to new species over long time periods. Darwin Adaptation to specific environment Only heritable traits Natural selection (short giraffes don t make as many babies) Lamarck Progression towards perfection Acquired characteristics Inner drive by the organism (i.e. giraffe stretches to reach tree) The first published work about natural selection was not by Darwin, but by Alfred Russell Wallace. Wallace published a paper on natural selection in Darwin just happened to make it to fame first. However, he waited 30 years before publishing his ideas on evolution. He published On the Origin of Species by Means of Natural Selection in Mechanism for evolution is natural selection Darwin didn t use evolution, but rather descent with modification Descent with Modification all species originated from the same species, but over time, an accumulation of slight modifications led to all the diversity we have on Earth today. Linnaeus theories on taxonomy fit this view organisms are grouped based on common ancestors and more similar organisms are more closely related. 2

3 A physical trait that provides a benefit to an individual in survival or reproduction Natural selection leads to an accumulation of adaptations Darwin's main focus the mechanism of evolution Definition: differences in survive and reproduction among individuals in a population as a result of their interaction with the environment Some have alleles that generate traits enabling them to cope better in their environment than others More successful individuals produce more offspring The quick version of natural selection: Everyone wants to reproduce. They don t or can t. There is competition. Everyone is different, and differences are genetic. Survive and reproduction depend on genes. Adaptive genes survive and become common. 1. Overproduction: Populations produce more offspring than can possibly survive. Overproduction leads to competition. 2. Natural Variation: Individuals in a population vary extensively from each other, mostly due to inheritance. 3. Fitness: struggle to survive, individuals whose inherited characteristics best fit to environment leave more offspring than less fit. 4. Adaptation: enhance an organism s ability to survive and reproduce 5. Descent with modification: Unequal ability of individuals to survive and reproduce leads to gradual change in population, with favorable characteristics accumulating over generations. Populations evolve, not individuals. Fitness is determined by the environment. In summary: Natural Selection = Differential success in reproduction Product of natural selection = Adaptations of populations to environment 1. Populations possess an enormous reproductive potential. Two elephants could produce 19 million individuals after 750 years if all offspring survived to reproductive maturity, and fostered a normal number of offspring. 2. Populations fluctuate around a constant size, remaining stable. 3. Resources, like food, water, or light, are limited and do not increase as populations grow larger. 4. Individuals compete for survival. Eventually, the needs of a growing population will exceed available resources. This causes competition. 5. There is variation among individuals in a population. Most traits have considerable variety (hair, skin, and eye color, height, etc.) 6. Much variation is heritable. Darwin recognized that traits were passed parents offspring, contrasting with the acquired characteristics view. 7. Only the most fit individuals survive. Survival of the fittest occurs because individuals with adapted traits are able to out-compete those that aren t so adapted. 8. Evolution occurs as favorable traits accumulate in the population. The individuals with the best traits usually make the most offspring. Over time, the best traits and alleles that generate them accumulate in the population. Superior inherited traits are adaptations, and increase an individual's fitness Fitness is the relative ability to survive and leave offspring (REPRODUCTIVE SUCCESS) It means the most capable of reproduction, NOT bigger, stronger, faster, or smarter Survival of the most fit genes or traits When the environment favors a trait (when the trait increases the survival of its bearer) selection is said to act for that trait Selection is said to act against unfavorable traits favorable ones are adaptive, while unfavorable traits are maladaptive 3

4 Natural selection may affect populations in a variety of ways. In ALL cases, natural selection acts on individual phenotypes already present in the population. Alleles may be expressed with other alleles in new combinations (as a result of genetic recombination) to crease novel phenotypes, or new phenotypes may appear in the population as a result of mutations. It is important to note that natural selection does NOT cause mutations or create new phenotypes it only SELECTS phenotypes already present in the population that maximize fitness. Stabilizing selection Directional selection Disruptive selection (diversifying selection) Sexual selection Artificial selection Eliminates individuals that have extreme or unusual traits Individuals with the most common form of a trait are the best adapted, while individuals who differ from the common form are poorly adapted Stabilizing selection maintains the existing population frequencies of common traits while selecting against all other trait variations Favors traits that are at one extreme of a range of traits traits at the opposite extreme are selected against If directional selection continues for many generations, favored traits become more and more extreme, leading to distinct changes in the allele frequencies of the population Examples: Darwin finches, peppered moths (industrial melanism), insecticide resistance, season creep (short winter/early spring) Also called diversifying selection Occurs when environment favors extreme or unusual traits, while selecting against the common traits Example: weeds tall forms dominate, but because of disruptive selection, weeds in people s yards only grow short because they escape mowing; weeds are mostly tall in the wild because tallness makes them better competitors for sunlight Differential mating of males (sometimes females) in a population In reproduction, females usually make a greater energy investment they increase fitness by increasing the quality of their offspring with superior males; males just try to make more babies Traits (physical qualities or behaviors) that allow males to increase their mating frequency lead to an increase in frequency of these traits within the population This leads to two kinds of sexual selection: Male competition: contests of strength that award mating opportunities to the strongest males (antlers, horns, large stature, etc.) Female choice: traits or behaviors in males that are attractive to females (bird plumage, elaborate mating behaviors) Sexual selection often leads to sexual dimorphism, differences in the appearance of males and females when this occurs, sexual selection is a form of disruptive selection 4

5 Form of directional selection carried out by humans when they sow seeds or breed animals that possess desirable traits It is not natural selection, but is given for comparison Various breeds of dogs have originated as a result of humans breeding animals with specific desirable traits Brussels sprouts, broccoli, cabbage, and cauliflower are all varieties of a single species of wild mustard after artificial selection of offspring possessing specific traits Natural Selection Nature decides Works on individual eg. Finch beaks Artificial Selection Man decides Selective breeding Inbreeding occurs eg. Breeds of dogs Mutations spontaneous accidental changes in an organism s DNA Very rarely beneficial, but does occur Or new combinations of existing genes Disney Version Populations change over time and everyone is happy! Organisms become more complex and better Everything gets better and the world is happy Real Talk Most individuals die off without reproducing, especially when the environment changes The survivors are different from the original population Estimated 99.9% of species that ever existed are extinct It creates new traits in times of need. Selection can only edit existing variations. Also, they are not helpful or convenient traits, just those that affect survival or reproduction. Individuals evolve or change over time. It is a mindset of trying to survive and reproduce. It s all about getting bigger, faster and stronger etc. Adaptations are often compromises rather than improvements. Organisms won t go extinct because they will evolve. Evolution is random. 5