Download Developing a Theory

Developing a Theory
C-16-1
Evolution is the process by which species may change
over time.
A theory is a broad explanation that has been
scientifically tested and supported.
belief = conclusion held with confidence but not
substantiated by positive knowledge or proof
The origin of life has many theories and ideas and has
been pondered for centuries!
Some alternative thoughts and theories…
Extraterrestrial Origin (Intelligent Design):
*life came from outside earth
Divine Creation
*life came from a divine being(s) or force.
Spontaneous Origin
* development through natural chemical and physical
processes
Theory of Evolution:
Presented by Charles Darwin in 1859 - has 4 major
points:
1.) Variation exists within the genes of every species
(result of random mutation)
2.) In a particular environment, some individuals of a
species are better suited for survival and so leave more
offspring
3.) Over time, change within a species leads to the
replacement of old species by new species as the less
successful species become extinct.
4.) There is clear evidence from fossils and many other
resources that the species now on Earth have evolved
(descended) from ancestral forms that are extinct
(evolution).
Darwin was a naturalist at heart and actually had a
degree in Theology!
Studied as a naturalist on the H.M.S. Beagle in 1831
where he made his observations and compiled his theory.
*Originally believed that divine creation was the
explanation
*This view did not account for kinds and distribution
fossils found
*found on his voyage, similarities and differences
between animals of the same species
Ex: fossilized armadillos looked similar, but not
identical to today's armadillos
ie: one gave rise to the other
Galapagos Islands: found the plants and animals closely
resembled those in nearby S. America
Ex: Finches - found many species that all looked very
similar but had different feeding habits… all looked
similar to a finch in S. America
* These birds must have migrated there and changed
after they arrived - descent with modification
Darwin actually bred pigeons to track traits…
~ by choosing which birds to breed, he was using a
process called artificial selection - done by humans
instead of nature
Most scientist of this time thought that species stayed
the same throughout time. This did not explain the fossil
record though!
Other scientists influenced Darwin's ideas:
Lamarck - use or disuse causes structures to enlarge or
shrink and stated that all such changes were heritable
Ex: giraffes stretched their necks to eat leaves =
offspring had longer necks
Darwin did not buy this idea, but agreed that traits were
passed down to offspring.
Lyell, Cuvier, and Hutton - studied fossils
* Cuvier thought the fossils showed change in
species but the change was sudden, not gradual
* Lyell and Hutton thought it was a gradual change ~ Lyell published a book on the topic:
~ showed earth's history was long enough for gradual
change to happen
Applying Darwin's Ideas
C-16-2
Natural Selection:
~ The process by which populations change in
response to their environment
Population: group of individuals that belong to the
same species, live in a defined area, and breed with
others in the group
Darwin looked to Malthus's ideas about population to
come up with the idea of natural selection…
Malthus said…* even though life has the potential to
reproduce to capacity in a short time, it does not due to
death from sickness, war, and starvation
So… Darwin's idea of natural selection states
* Individuals that possess superior physical or
behavioral attributes are more likely to survive than
those that are not so well endowed.
4 logical steps to explain this…
1.) Overproduction - all species are capable of
making more offspring than will survive to
maturity
2.) Variation - variation exist within every population
- much in the form of inherited traits
3.) Selection - in any environment, a given trait may
make individuals more or less likely to survive to
reproduce. Those who survive - pass on genes
to their offspring
4.) Adaptation - over time, those traits that
improve survival and reproduction will become
more common
In 1859, he published On the Origin of Species by Means
of Natural Selection
* Gave a huge amount of evidence that evolution had
occurred and also provided a reasonable hypothesis for
how evolution takes place.
Fossils:
These are the most direct evidence for
macroevolution
~ Fossils are the preserved or mineralized remains or
traces of dead organisms
Ex: fossils in older rocks are different than
fossils in newer rocks
remains = bone, teeth, shells
traces = footprints, burrows, imprints
Scientists are always looking for "intermediate species"
or missing links…
Some links have been discovered:
* fish and reptiles
* reptiles and birds
* reptiles and mammals
Look at Figure 7 pg. 382 this shows the hypothetical
descent of whales from 4 legged land animals.
Sadly, the fossil record is incomplete!
Some species lived where they were not easily fossilized
so we have lost the record of them.
~ For an org. to be fossilized, it must be quickly
covered by fine sediment before the body decays, is
eaten, or is scattered by scavengers.
Good places to be fossilized = wet lowlands, slow moving
streams, shallow seas, near volcanoes
By using carbon dating, paleontologists can tell how old a
fossil is - this allows them to put the fossils in order and
come up with a family tree and show common ancestors.
Ex:
Common ancestor = species from which 2 or more species
diverged
We can also use genetics to note links between species:
~ We can trace the genetic mutations back to see how
far removed one org. is from another!
Ex: our hemoglobin has a 146 AA chain …
*a gorilla has a hemoglobin 146 AA chain with only
one different AA from us!!
This shows that we share a common ancestor that was
very recent!
If there are many differences, then the common
ancestor is in the distant past.
Now, we can chart the genetic code and show side by side
where the differences are in the nucleotides!
We use this to make family trees.
Anatomy and Development:
Looking at the skeletal structure of vertebrates, we can
see common ties…
Ex:
These are homologous structures = they share a common
ancestry!
Organisms that have bones or other structures that are
reduced in size or are modified are said to be vestigial
structures
Ex: our coccyx (tailbone) does not have the same use as a
fish's tail
Beyond Darwinian Theory
C-16-3
1.) Microevolution occurs as a result of genetic mutation
within species over a long period of time.
2.) Isolation will lead to species formation = speciation
~ this is the link bet. macro. and microevolution!
isolation = two populations of the same species are
separated by a landform or other
obstacle
species = when individuals of two populations can no
longer interbreed
Ex:
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display
Speciation

Four steps lead to speciation. First, a single species is an interbreeding reproductive
community. Second, a barrier develops, dividing the species. Third, separated into different
habitats, the divided populations become differentiated through the accumulation of
differences. Fourth, so different have the separate populations become, that is when the
barrier disappears and they overlap again. Interbreeding does not occur.
3.) Extinction leads to species replacement
When a species dies out completely, those that are
left continue to live
Ex: Reptiles once ruled the earth - due to climactic
changes, they were replaced more dominantly by
mammals
This is called macroevolution!
So how do these things happen?
Microevolution:
These are factors that will affect what kind of genes are
in a pop. from one gen. to the next:
* Natural selection - can cause increase or decrease in
certain alleles in a population
* Migration - moving individuals in, out, or between pop's
- can change numbers in types of alleles in a pop.
* Mate choice - randomly paired parents = random
assortments of traits
- selective or limited choices = limited set of traits
passed on
* Mutation - change # and types of alleles from one
generation to the next - these are rare
* Genetic drift - random effects of everyday life cause
differences in the survival and reproduction of
certain individuals
- therefore, some alleles may become more/ less
common
Macroevolution
* Convergent evolution - species living in similar
environments should evolve similar adaptations
* Coevolution - species who live closely together will
have adapted to one another's existence
Ex: the orchid moth - only this type of moth feeds
on this orchid and they depend on one another for their
existence
* Adaptive radiation - over time, species may split into 2
or more lines of descendants (lineages). Many splits
yields many different species.
* Extinction - all members of a lineage die out
* Gradualism - slow, gradual change of differences build
up over time to equal large change
* Punctuated equilibrium - due to environmental change,
some species will change rapidly or "suddenly" appear.
If the climate changed drastically, those species that
could adapt quickly would be more likely to survive!
This provides backing for punctuated equilibrium!
Ex: volcanic eruptions, ice ages, asteroid impacts etc.
Many species that cannot adapt will succumb to these
disasters! ~ This will leave room for species replacement
and evolution.
Both of these ideas have their followers, but most
support gradualism.