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what is evolution?

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evolution means in Latin "evolutio", or, "                  unrolling"

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in everyday language we use the word evolve in many ways, e.g. attitudes evolve, the earth evolves,           ideas evolve, our solar system evolves

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however,                     biologists are much more specific in using the term evolve

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not every kind of biological change is an evolutionary change

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understanding how evolution has contributed to life's                   diversity helps us understand some diversity is not explained by evolution but other processes

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the biological definition of evolution is:               genetic change of a population over time

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evolution is not change in an                     individual even though genetics inside our bodies can change during our lifetime, e.g. when someone has             cancer, i.e. the genetics inside of a cell have changed , these are "somatic" genetic changes, or "of the body", i.e. those cells that are not involved in reproduction

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none of the changes that occur to you during the course of your lifetime are evolution

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the composition of a             forest changes over time

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different trees, different amounts of plants, animals are changing

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these are not evolutionary changes since they don't involve reproduction but just changes in the                       composition of a whole

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the population of oak trees may be evolving but from the point of view of the forest, these composition is simply changing, the community is changing, not an organism that reproduces similar copies of itself

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evolution always involves a genetic change

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if we are looking at changes caused by the environment, we are not talking about evolutionary change

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e.g. people are living longer now in many populations

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that is a systematic change that has happened because of better                   nutrition and conquering various diseases

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we are not living longer because our genetics are changing

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the human genome consists of 3 billion                       nucleotides

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6 billion bases of DNA, any of these can         flip as a single point mutation and if this helps the organism survive to give birth, it may pass on this mutation, which may also help offspring survive till reproduction

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good example in humans:

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              lactase persistence: the ability beyond childhood to digest milk

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lactase's only function is the digestion of lactose in milk, in most mammal species the activity of the enzyme is dramatically reduced after weaning

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sometimes not just bases of DNA can change but whole                       chromosomes can change

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can lead to large scale evolutionary change

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much of evolution's changes are             random

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most of our genomes have no affect on our physical form or behavior

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a change to any part of that is unlikely to change anything about us

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only relatively few changes occurred through natural selection

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most are simply random

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even a mutation which gives an organism a particular advantage to survive till reproductive age, depends on many random factors that it will indeed reach reproductive age

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almost all mutations in populations will disappear rapidly, since in order to cause the organism to evolve, it not only has to give the organism some kind of advantage, it also has to make it into the offspring of that individual

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e.g. an organism with a                     beneficial mutation may have x number of offspring and none of those offspring have that mutation passed into their genes

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hence random change plays a large role in whether beneficial factors survive in populations

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most mutations are           muted within a specifies since they don't bring advantage to the organism and often bring a disadvantage

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natural selection is there, in the long term, shaping the genome

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but evolution is not                     completely random

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natural selection encourages not just any genes to be passed on, but those which organism who have survived until                     childbirth have, which over time are generally different than those which have not survived in the environment

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when populations reach numbers where there are too many to support, there is therefore                       competition in which natural selection plays more of a role and the strongest, most well-adapted to the environment tend to survive and procreate

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a beneficial gene is governed by chance as to whether it will be established in the organism

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evolution cannot be                   prevented

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we can imagine a population where every individual had the exact same number of                   offspring, every individual had exact and perfect copying of its genome in every generation

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that's what it would take to stop evolutionary change

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even natural populations which are             clones

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e.g. clonal populations of                 bacteria are rapidly evolving because the genetic copying is not exact, and mutations are being constantly introduced which determine which individuals can clone themselves

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our understanding of biological evolution today is not the same as in             Darwin's time

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in particular, we have learned much more about the connection between genetic change and changes in physical form and behavior

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we can predict outcomes of evolutionary change in ways that Darwin could not

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Darwin was fundamentally important to the development of our understanding of evolution, mainly with           three ideas

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1. natural selection

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in most populations there is a struggle for                 survival, and organisms that are slightly better fitted to survive in that population's environment tend to win out in that struggle and therefore their characteristics will be better represented             future generations

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2. common               descent

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organisms that exist in the world today come from common organisms that existed in the past and that the relationships between organisms can be represented as an evolutionary tree

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3. very slight changes in one generation can lead to large changes in the species over longer periods of time

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we have gone beyond Darwin's understanding of                     biological evolution

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we understand how                             mathematically how populations evolve over time because of changes in the composition of genetics

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we understand on a                   molecular basis how genetic changes are introduces in populations and the different kinds of genetic changes that can happen

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we understand about the developmental connections between genes, and the form and behavior of the organism

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studying evolution today is a scientific enterprise which gives us                       explanatory power about the patterns of variability that we see in nature, about the                 patterns that we see and the patterns that we don't see