Download EVOLUTIONARY THEORIES

EVOLUTIONARY THEORIES
Over the years, there have been many theories on evolution.
(1) Branching Theory * most scientists agree with the theory that living things have changed,
from simple organisms to complex organisms, over a long period of time
* species that are most closely related share a more recent common
ancestor while distantly related species have a common ancestor further in the
past
Tree Diagram
(2) Spontaneous Generation –
* the concept that living things come from nonliving things
* ex – flies came from the rotting bodies of animals
* this theory made sense to people because they could not see the tiny
eggs laid by organisms, therefore, they didn’t know organisms came from the
eggs
(3) Theory of Use and Disuse –
* early 1800s
* proposed by
__________________________________________________
* organisms develop new structures because they need them
* these structures become ___________________
_______________________, which is a trait produced during an individual/s
lifetime and these useful traits are then passed onto the organism’s offspring
* example –

the Theory of Use and Disuse was disproved by
___________________________, who performed experiments with
mice
(4) Theory of Natural Selection –
* proposed by ___________________________________________ in
the 1850s
* stated that evolution occurs because of natural selection
* nature acts as a selecting agent of an organism’s traits
* traits that help an organism survive in a changing environment are
passed on o the next generation
Darwin’s Theory of Natural Selection
(A) Overproduction: A population generally produces more offspring than
can survive in the environment
(B) Competition: Because of overproduction, there is competition, or a
struggle for survival, between organisms for space, food, water, light,
minerals, and other limited resources
(C) Variations: Members of a population show variations (differences) in
traits that make certain individuals better adapted to survive. Differences
in structure, size, and color are examples of variation.
(D) Natural Selection: Since some variations are more helpful than others,
there is a natural selection against organisms that cannot adapt.
Organisms that cannot adapt die.
(E) Survival of the Fittest: Survival of the fittest applies to those individuals
that have variations that enable them to live and reproduce. Ex – in a
woodland area, brown fur would be advantageous over white fur (could
blend in)
(F) Inheritance of Variations: Organisms with helpful variations are more
likely to survive and to reproduce, passing these helpful variations to the
next generation (offspring).
(G) Evolution of New Species: Over long periods of time, variations
accumulate in a population. Eventually there are so many variations that
the population changes. This is called
_____________________________________.

Darwin’s theory was not accepted right away – he could not explain
one aspect of his theory –
What were the major differences between Darwin’s and Lamarck’s two theories?
(5) Mutation Theory –
* 1901 - Hugo De Vries
* experimented with the plant, evening primrose
* determined that variations came from
_____________________(changes in genetic material) which occurred randomly
and those ___________________ that were favorable were inherited by
offspring
(6) Modern Theory –
* combines Darwin’s ideas of variation and natural selection with recent
studies of mutations, DNA, genes, chromosomes, and sexual reproduction and
genetic recombination
Modern Theory of Natural Selection
(A) The genes of inherited variations that give an organism a better chance for
survival tend to be passed on from parent to offspring. These new
inheritable characteristics can result from new combinations of existing
genes or from mutations of genes in reproductive cells.
(B) Favorable genes tend to increase in numbers within a population because
some characteristics give individuals an advantage over others in
surviving and reproducing, and the advantaged offspring, in turn, are more
likely than others to survive and reproduce.
(C) Genes for traits with low survival value decrease in numbers from
generation to generation.
(D) If the environment changes, genes that previously were neutral or had low
survival value may become favorable and increase in numbers. The
variation of organisms within a species increases the possibility that at
least some members of the species will survive under changed
environmental conditions.
How does the Modern theory of evolution use Darwin’s ideas?