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C O U R S E 
Human Evolution: Past and Future
John Hawks, University of Wisconsin
C O U R S E   L E C T U R E 
What is Biological Evolution?
Notes taken on May 23, 2014 by Edward Tanguay
what is evolution?
evolution means in Latin "evolutio", or, "unrolling"
in everyday language we use the word evolve in many ways, e.g. attitudes evolve, the earth evolves, ideas evolve, our solar system evolves
however, biologists are much more specific in using the term evolve
not every kind of biological change is an evolutionary change
understanding how evolution has contributed to life's diversity helps us understand some diversity is not explained by evolution but other processes
the biological definition of evolution is: genetic change of a population over time
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
none of the changes that occur to you during the course of your lifetime are evolution
the composition of a forest changes over time
different trees, different amounts of plants, animals are changing
these are not evolutionary changes since they don't involve reproduction but just changes in the composition of a whole
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
evolution always involves a genetic change
if we are looking at changes caused by the environment, we are not talking about evolutionary change
e.g. people are living longer now in many populations
that is a systematic change that has happened because of better nutrition and conquering various diseases
we are not living longer because our genetics are changing
the human genome consists of 3 billion nucleotides
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
good example in humans:
lactase persistence: the ability beyond childhood to digest milk
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
sometimes not just bases of DNA can change but whole chromosomes can change
can lead to large scale evolutionary change
much of evolution's changes are random
most of our genomes have no affect on our physical form or behavior
a change to any part of that is unlikely to change anything about us
only relatively few changes occurred through natural selection
most are simply random
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
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
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
hence random change plays a large role in whether beneficial factors survive in populations
most mutations are muted within a specifies since they don't bring advantage to the organism and often bring a disadvantage
natural selection is there, in the long term, shaping the genome
but evolution is not completely random
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
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
a beneficial gene is governed by chance as to whether it will be established in the organism
evolution cannot be prevented
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
that's what it would take to stop evolutionary change
even natural populations which are clones
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
our understanding of biological evolution today is not the same as in Darwin's time
in particular, we have learned much more about the connection between genetic change and changes in physical form and behavior
we can predict outcomes of evolutionary change in ways that Darwin could not
Darwin was fundamentally important to the development of our understanding of evolution, mainly with three ideas
1. natural selection
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
2. common descent
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
3. very slight changes in one generation can lead to large changes in the species over longer periods of time
we have gone beyond Darwin's understanding of biological evolution
we understand how mathematically how populations evolve over time because of changes in the composition of genetics
we understand on a molecular basis how genetic changes are introduces in populations and the different kinds of genetic changes that can happen
we understand about the developmental connections between genes, and the form and behavior of the organism
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