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Unformatted text preview: Evolution
A continuous process of change that produces a series of transformations. 1. Biological Definitions: A change in the genetic frequency of a trait in a population or species over time. Evolution
Evolution From the Simpsons™ by Fox Evolution
2. A change in gene frequency through time resulting from natural selection that produces cumulative changes in the characteristics of a population. Evolution
Note: Evolution occurs at the level of the population (not the individual), even though natural selection usually works at the level of individuals. Evolution
Evolution Evolution is the major unifying theme in biology, geology, and other natural sciences, but especially in natural history, taxonomy, ecology, developmental biology, and genetics. Evolution
Evolution With the possible exceptions of certain forms of physics (mechanics) and inorganic chemistry, the sciences are steeped in evolutionary thought. Evolution
Evolution Evolution is the central unifying concept of biology. Evolution
Evolution Evolution is about change. But change itself is a constant theme in all of the sciences. Evolution
Evolution From astronomy we know that galaxies are changing; stars develop and burn out. NO! Not this kind of star! Evolution
Evolution Geologists have discovered that continental tectonic plates are constantly moving (Continental Drift) changing the face of the Earth as well as the sea floor. Evolution
Evolution Mountains grow and then decay through erosion.
The Appalachian Chain was once as mighty as the Rockies and the Andes. Everything east of Interstate 95, known as the Coastal Plain, is the product of the erosion of these once great mountains. The light area is the Piedmont; east is the Coastal Plain. Evolution
Evolution The Earth’s atmosphere has changed throughout the history of the Earth as a planet. The amount of oxygen, as well as the amount of carbon dioxide, in the atmosphere has changed throughout the Earth’s history. Evolution
Evolution The amount of O2 in the present atmosphere is a by
product of the evolution of photosynthesis by cyanobacteria! Evolution
Evolution It is therefore obvious and logical that biological species would have appeared and disappeared as the Earth has changed; this fact has been made abundantly clear from the fossil record. Evolution
Evolution Evolution is affirmed by: 1. geology, 2. the fossil record, 3. radioactive dating, 4. ice, mud and rock cores taken from lake and ocean bottoms, and by 5. molecular and developmental biology. Evolution
Those who study evolution consider it to be an empirical fact. The term “theory” misleads some people. The word does not mean “a hypothesis proposed as an explanation.” Evolution
Evolution “Theory” means, “a statement of general laws, principles, or causes of something known or observed.”
This is how the term applies to evolution. Evolution
Evolution Evolutionary theory is no less well founded than: “Cell Theory,” the “Germ Theory of Disease,” and the “Theory of Relativity” of Einstein. Evolution
Evolution We should recall that the germ theory of disease was not well accepted until late in the 19th century. Evolution
Evolution On a small scale, evolution can be regularly observed in contemporary time. Evolution
In summary: Evolution is supported from a wide variety of geological, molecular, geographical, anatomical, developmental and biochemical evidence. Evolution
Evolution The Darwinian postulates of evolution: 1) Variation exists within and between populations for any given trait (Variation arises through mutations). 2) The genetic traits of organisms are inherited from their parents. Evolution
3) Normally, many more individuals are produced than can survive. 4) The process of natural selection preserves the most fit. Evolution
Evolution The power of selection is affirmed by cultural or artificial selection which has been used to produce the disparate breeds of animals and plants that have been produced by mankind in remarkably short periods of time. Selection in Cabbage
Selection in Cabbage Consider the domestication of Brassica oleracea (wild cabbage). In domestic cabbage, we have massively enlarged the terminal bud. Selection in Cabbage
Selection in Cabbage In kale, the stem leaves have proliferated and curled. Selection in Cabbage In brussels sprouts, the side buds are numerous and highly compacted; Selection in Cabbage In cauliflower, the immature terminal flower head is swollen; Selection in Cabbage
Selection in Cabbage In broccoli, the side branches have been selected to carry small heads of edible flowers; Selection in Cabbage
Selection in Cabbage In kohlrabi, artificial selection has produced a swollen stem base that looks like a turnip with leaves sprouting from the sides. Selection in Cabbage
Selection in Cabbage In all of these cases, in addition to selection of the physical characteristics of the plant, the bitter taste of the wild relative has been bred out. Human Evolution versus Human Evolution versus Cultural Evolution Biological evolution depends upon natural selection, which requires a Mendelian form of inheritance, based on small scale undirected variation. Human Evolution versus Human Evolution versus Cultural Evolution Evolution proceeds by division of species into independent lineages separated on the branching tree of life. Human Evolution versus Human Evolution versus Cultural Evolution Human cultural change works by the opposite process, one of borrowing and amalgamation. A biological analog of cultural change might be infection. Human cultural change operates through the Lamarkian idea of acquired characteristics. Human Evolution versus Human Evolution versus Cultural Evolution Ideas from one generation are passed on to the next. Cultural change now overwhelms the much slower process of Darwinian natural selection in humans. Parallel versus Convergent Parallel versus Convergent Evolution Parallel evolution
Evolution of similar adaptations among groups that have a common origin, but which were geographically separated at an early stage in their history. Example: marsupial and placental mammals. Parallel versus Convergent Evolution Convergent evolution
Evolutionary lines far removed from each other, evolve similar traits in response to similar environmental conditions. Examples: Desert adaptations among plants, swimming carnivores. Convergent Evolution
Convergent Evolution In convergent evolution, when environmental conditions are similar in different parts of the world, evolution has fashioned similar looking organisms (same adaptations) but using different starting materials. Convergent Evolution
Convergent Evolution For example the Cactus family is found only in the Americas and the Euphoriaceae are found in Africa and other parts of the old world deserts. What people call “cactus” in Southern Africa are actually plants from the Apocynaceae (dog bane, milkweed) family.
The flowers and molecular data tell us that the three groups that are very distantly related, but the adaptations to drought are very similar. American Cactus African Euphorb Parallel versus Convergent Parallel versus Convergent Evolution In convergent evolution, the organisms are more distantly related and may be sympatric (living in the same geographical region). Parallel versus Convergent Parallel versus Convergent Evolution In parallel evolution, the organisms are geographically separated (allopatric) and are recognized as having a more similar evolutionary origin than in convergent evolution. Parallel versus Convergent Parallel versus Convergent Evolution But the distinctions between convergent and parallel evolution are sometimes a matter of opinion or preference. What is a Species?
What is a Species?
The word species means “form or kind” in Latin. Since the term species is so fundamental in biology, it may seem surprising that there is disagreement as to the definition of a species. What is a Species?
What is a Species? Darwin warned that no definition for species would satisfy everyone, since it would be trying to “define the undefinable”. What is a Species?
What is a Species? In the 20th Century biologists used the “biological species concept”. According to this definition, we assume that species are separated by a “reproductive isolating mechanism”. What is a Species?
What is a Species? For example, species may mate at different times of day, their eggs and sperm may be incompatible, they may lack the proper signals (visual, olfactory etc.) that would encourage mating, or genetic incompatibilities may prevent their offspring from surviving or being fertile. What is a Species?
What is a Species? Another definition for a species is based on molecular studies. A species is viewed as a “distinct cluster of genes”. A population sharing enough similar genes is considered to be the same species. What is a Species?
What is a Species?
Many organisms, however, which are generally agreed upon as distinct species, are known to interbreed and produce hybrids. This is particularly true in the dog family (Canidae). What is a Species?
What is a Species? What, if anything, is a dog? Dog (Yellow Labrador) versus Dog (Yellow Labrador) versus Wolf Chihuahua versus Dalmatian
Chihuahua versus Dalmatian What is a Species?
What is a Species?
The dog is now known as: Canis lupus familiaris Which means it is a subspecies of the wolf! What is a Species?
What is a Species?
Coyotes, dogs and wolves are able to interbreed and regularly do so. The number of breeds of dog are a testament to the genetic diversity of the dog family. What is a Species?
What is a Species?
The taxonomic status of the red wolf is a case in point. Based on morphological and biogeographic data, the red wolf was considered to be a distinct species. Red Wolf
Red Wolf Early, molecular studies seemed to show that the red wolf was either a subspecies of the gray wolf, or a cross between the gray wolf and the coyote. Red Wolf
Red Wolf But the most recentstudies seem to favor the idea that the red wolf was a distinct species! But its gene pool has been contaminated with alleles from dogs, coyotes and gray wolves. What is a Species?
What is a Species? Other examples: The Baltimore oriole of the east and the Bullock’s oriole of the Great Plains of North America, interbreed freely, producing a hybrid zone.
Northern pintail ducks interbreed regularly with mallard ducks. What is a Species? What is a Species?
What is a Species? Horses and zebras can interbreed, though they would not do so in the wild. The Allopatric Model of The Allopatric Model of Speciation
1. A species is divided into two populations that are geographically isolated from each other (an allopatric distribution). The Allopatric Model of The Allopatric Model of Speciation
2. There is no gene flow between the two populations. The Allopatric Model of The Allopatric Model of Speciation
3. Each population, though derived from the same gene pool, is genetically distinct due to finite (often small) population sizes resulting in “sampling error”. The Allopatric Model of The Allopatric Model of Speciation
4. Each population finds itself in a unique environment in which natural selection follows a slightly different course. 5. Therefore, each population diverges genetically from the original gene pool. The Allopatric Model of The Allopatric Model of Speciation
6. The two populations are isolated for a long period of time. The Allopatric Model of The Allopatric Model of Speciation
7. Eventually, enough genetic changes accumulate such that, if the two populations are brought back into contact with one another, they are no longer able to interbreed and produce viable offspring. The Allopatric Model of The Allopatric Model of Speciation
8. At this point, they are recognized as two different “biological species.” Biological speciation is not frozen in time; it continues today. Gray Fox Gray Fox (Urocyon cinereoargenteus) The Gray Fox is smaller in size than the Coyote usually 32 to 45 inches long, and weighs 7 to 11 pounds. Channel Island Fox
Channel Island Fox
(Urocyon littoralis) Environmental and ecological factors such as drought or food scarcity may have contributed to the natural selection for a smaller size. At 12 to 13 inches in height and 4 to 5 pounds, the island fox is about the size of a housecat. The Allopatric Model of The Allopatric Model of Speciation When speciation is ongoing, particularly if the geographical isolation is not complete, the populations may become classified by biologists as “subspecies”. See example of Plethodon jordani salamanders. Ecotypes
Ecotypes What is an Ecotype? 1. A genetically differentiated population within a species, the differences having ecological significance. Ecotypes
2. A genetically distinct population of the same species. 3. A genotypic response, through natural selection, to the environment. Ecotypes
In this case, geographical isolation is incomplete and the differences among the populations are not significant enough to be raised to the level of “subspecies”. Ecotypes
Ecotypes Adaptation A. A genetically determined characteristic that enhances the ability of an individual to cope with its environment; B. An evolutionary process by which organisms become better suited to their environments. Ecotypes
A phenotypic response to the environment, often a reversible charge in the morphology or physiology of an organism in response to an environmental change. Ecotypes
Ecotypes In 1922, the Swedish Botanist Turesson began looking at phenotypic variation in different environments. He examined two populations of the plant, Plantago maritima.
One population was growing on sea cliffs; a second grew a few hundred meters away in a fresh water marsh. Ecotypes
Ecotypes On the sea cliff, the plants were exposed to salt spray and constant high winds. The plants on the sea cliffs were dwarfed compared to the marsh plants. Ecotypes
Ecotypes The marsh was an environment protected from the high winds and salt spray. There the plants were tall and robust. Ecotypes
The question Turesson asked was: Are these height differences the result of simple acclimation, or had natural selection produced two different genetic populations or “ecotypes?” That is, were there genetic differences between the marsh and the sea cliff populations? Ecotypes
Ecotypes To answer these questions, Turesson gathered seeds from both plant populations and grew them in a common, neutral environment, the greenhouse. The results are as displayed below. Ecotypes
Environment Mean height Mean height Natural Greenhouse Marsh Environment
35.0 cm 31.5 cm Sea Cliff 10.0 cm 20.7 cm Ecotypes
Ecotypes The results show that the height differences in the natural environment are due to a combination of acclimation and genetic adaptation through natural selection. Ecotypes
Ecotypes The sea cliff population has the genetic ability to grow to 20.7 cm under favorable conditions, but is only 10.0 cm at the sea cliff. Ecotypes
Ecotypes Therefore, some of the dwarfing in this population is due to acclimation to the harsh sea cliff environment. Ecotypes
Ecotypes However, by comparing the two populations in the neutral environment of the greenhouse, we see that there is also a genetic effect (adaptation). Ecotypes
By comparison, to the marsh population, natural selection has favored genes for small plants at the sea cliff. Therefore, there is a genetic component to the height difference between the two populations. Ecotypes
Ecotypes Accordingly, we can say that there exists a marsh ecotype and a sea cliff ecotype within the species, Plantago maritima. F i g u r e 2 Camouflaging color patterns of mice from different habitats. Oldfield mice (Peromyscus
polionotus) can be found in two distinct habitats in Florida—oldfields which are vegetated and
have dark loamy soil, and coastal sand dunes which have little vegetation and brilliant white sand.
Mice that occupy these different habitats have distinct coatcolor phenotypes: mainland mice have a
typical dark brown coat, whereas beach mice largely lack pigmentation on their face, flanks and tail.
Typical habitat, soil samples and mice are shown. [Sacha Vignieri (habitat), Clint Cook (mice)] Camouflaged mice have a 50% higher probability of “survival” compared to mismatched mice Cryptic Mice NonCryptic Mice References From Darwin to DNA: The Genetic Basis of Color
Adaptations H.E. Hoestra
From: In the Light of Evolution: Essays from the
Laboratory and the Field edited by Jonathan B.
Losos. 2011. Roberts and Co. Woodbury, New York.
Hoekstra, H. E., R. J. Hirschmann, R. A. Bundey, P.
A. Insel, and J. P. Crossland. 2006. A single amino
acid mutation contributes to adaptive beach mouse
color pattern. Science 313:101–104. Questions? ...
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This note was uploaded on 01/23/2012 for the course BIOL/EVPP 307 taught by Professor Crerar during the Summer '11 term at George Mason.
- Summer '11