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BIO120H1 Lecture Notes - Habituation, Molecular Evolution, Heritability

Course Code
June Larkin

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03/06/2012 22:45:00
Why Evolution Is True?
Chapter 1
So what is Darwinism?
The theory of evolution by natural selection
Life on earth evolved gradually beginning with one primitive species-
perhaps a self replicating molecule that live more than 3.5 billion
years ago; it then branched out over time, throwing off many new
and diverse species and the mechanism for most of evolutionary
change it natural selection
Consist of 6 components: evolution, gradualism, speciation, common
ancestry, natural selection and nonselective mechanisms of evolutionary
1. evolution: that species undergoes genetic change over time, that is, over
many generations a species can evolve into something quite different and
those differences are based on changes in the DNA, which originates as
2. Gradualism: it takes many generations to produce a substantial
evolutionary change such as the evolution of birds from reptiles. Gradualism
doesn’t mean , however that each species evolves at an even pace, when
natural selection is strong as when an animal or plant colonizes a new
environment evolutionary change can be fast.
3. Speciation(splitting): Single ancestral species that split into two
descendent species, one splits more and causing more species and the other
split causing other different species common ancestor is called the missing
link btwn two different descendant groups …what happens if ancestor x split
into two separate species? Nothing much
Speciation means the evolution of different groups that cant
interbreed that is groups that cant exchange genes ( why split
members of different animal species may no longer find each other
attractive or if they do mate with each other the offspring couple be
All the important change happed thousands of generations after the
split when selection acted on one linage to promote the flight and on
the other to promote the traits of bipedal dinosaurs

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Speciation doesn’t happen very often but each time one species
splits into two, it doubles the number of opportunities for future
speciation so the number of species can rise exponentially
3. Common Ancestry: it simply means that we can always look back in time
using either DNA sequences or fossils and find descendants joining at their
Backbone vertebrates all united by having amniotic egg-the
embryo is surrounded by fluid filled membrane called amnion
Hierarchy: a hierarchy in which big groups of species whose
members share a few traits are subdivided into smaller groups of
species sharing more traits and so on down to species like black
bears and grizzly bears that share nearly all their traits
The natural classification is itself strong evidence for evolution
By sequencing the DNA of various species and measuring how similar
these sequences are we can reconstruct their evolutionary
The idea of common ancestry leads naturally to powerful and
testable predictions about evolution
5. Natural Selection: if individuals within a species differ genetically from
one another and some of those differences affect an individual ability to
survive and reproduce in its environment, then in the next generation the
good genes that lead to higher survival and reproduction will have relatively
more copies than the not so good genes
the population will gradually become more suited to its environment
as helpful mutations arise and spread through the population while
deleterious ones are weeded out.
This process produces organisms that are well adapted to their
habitats and way life
Natural selection and evolution are inevitable
Natural selection must also work with the design of an organism as a
Mutations are changes in traits that already exist; they almost never
create brand new features, this means that evolution must build a
new species starting with the design of its ancestors
Natural selection only improves what came before . it produces the
fitter not the fittest
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