Download Evolution: Constructing a Fundamental Scientific Theory

Evolution: Constructing
a Fundamental
Scientific Theory
Chapter 2
Overview
We study both the past and present to understand
human evolution
Part I: observing living populations
Part II: study of ancestors
Introduction
1800s: explorations, discoveries of new lands, plants,
animals, and people
Fossils: preserved remains
Charles Darwin went on a 5 year voyage on the HMS
Beagle
Observed, studied, and collected specimens
Darwin
Began formulating questions about observations
Variation among and between species (finches)
Variation according to habitat
First explanation was “descent with modification”
Adaptations: variations in physical characteristics to
fit the environment
Two Major Findings
1. natural selection:
More individuals are born than can survive
Limited resources leads to competition
Those with advantages (adaptations) will survive and
pass down genes
Those without will die
Primary driver of evolution
2. adaptive radiation: out of one species branches
closely related multiple species
Natural Selection:
Practical Example
Natural selection is about biology, but in humans, it
is also about intellect/knowledge
If you were stranded on a desert island, would you
want the people you were with to be in shape, or to
have specialized knowledge?
What types of knowledge would be helpful?
The main point is that natural selection is about what
is advantageous in that specific environment at that
specific time
On the island, it may be helpful for an animal to be
fast, or small, or green
BUT, if the environment changes, this may not be the
case
A computer programmer may have been successful
beforehand, but will not have an advantage on the
island
Practical Example #2
Can you see viruses or bacteria?
They are alive and, like everything else, they evolve
Can evolve in a matter of hours
This is why not taking antibiotics/medication
correctly leads to drug resistance
When people do not take medication correctly
Yellow = weak viruses
Purple = medium viruses
Red = strong viruses
When people do not take medication correctly
Yellow = weak viruses
Purple = medium viruses
Red = strong viruses
Theory of Evolution
Evolution just means change over time
Here, it means change in gene frequency over
generations
Before Darwin, most explanations were based on
religious beliefs
Earth is 6,000 years old, everything is fixed
Darwin used 5 disciplines:
Geology, paleontology, taxonomy/systematics,
demography, evolutionary biology
Geology
Geology: study of earth in regard to composition,
activity, and history
Earth is 4.6 billion years old
Hutton and Lyell found that forces (rain, wind)
change the earth today just as they did in the past :
uniformitarianism
Also found that land’s surfaces get stacked on top of
each other: strata
These processes all take millions of years and can be
observed and tested
Paleontology
Georges Cuvier pioneered comparative anatomy and
paleontology
Reconstructed the appearance of fossil animals
Provided the first basic understanding of history of
life
Catastrophism: catastrophic events (not evolution)
are responsible for changes in Earth’s history
What is an example from the Bible?
What is an example from fossil history?
Taxonomy/Systematics
Taxonomies group living organisms according to
similarities
Carolus Linnaeus gave each organism a genus and
species: binomial nomenclature
At this time still adhered to biblical explanations.
Taxonomies showed God’s intentions
Also some ranking (hierarchy)
Organisms are fixed and don’t change
Taxonomy of Humans
Kingdom
Anamalia
Phylum
Chordata
Class
Mammalia
Order
Primates
Family
Hominidae
Genus
Homo
Species
sapiens
Demography
Darwin influenced by essay of Thomas Malthus
Said there was not enough food to feed every person
born
Darwin applied these ideas to other living things
Those that survive are the ones equipped to compete
for food and win
Evolutionary Biology
In late 1700s some scientists said organisms aren’t
fixed and that they do change over time
Lamarck first discussed adaptations
He was correct in saying that animals adapt to their
environment
Lamarkism or Prinicple of Acquired Characteristics:
organisms pass on features they acquire during their
lifetimes
Incorrect
hierarchy
Lamarckism
Example: if a giraffe needs to eat leaves at the very
tops of tall trees, it should stretch its neck until he is
the correct height. Then his offspring will be born
with long necks
If you chopped off both hands right now, would your
children be born without hands?
Why is Acquired Characteristics incorrect?
Darwin’s Theory of
Evolution
Darwin used all of these fields to shape his idea
He saw that those best suited for their environment
survived and passed down those traits. Those that
weren’t suited died
Nature puts pressure on living things and selects the
traits that are advantageous
Origin of Species (1859). After discovering and
Wallace had the same idea, Darwin beat him to
publication
ICA
Darwin vs. Lamarck
Since Darwin…Inheritance
and DNA
Darwin and scientists at the time thought body was
made of invisible particles called gemmules
Also thought blending inheritance
Gregor Mendel’s pea experiments uncovered idea of
inheritance and dominant and recessive traits
Discrete traits
Mathematical laws
NO BLENDING!
Model of Genetic
Events
Mendel said that inheritable traits keep their
individuality by not blending
Principle of Segregation: offspring receive traits
from parents, and the traits are kept in pairs that
separate during formation of sex cells.
Principle of Independent Assortment: inheritance
patterns of each trait are independent of one
another
each trait has an equal chance of being inherited
Mendelian Genetics
Later scientists would discover genes: a section of DNA
that codes for a trait and their alleles: different versions of
genes
Each allele is either dominant or recessive
Dominant: T
Recessive: t
One allele is from mom, the other is from dad
If both alleles are the same = homozygous
If both dominant = homozygous dominant
If both recessive = homozygous recessive
If one allele is dominant and one is recessive =
heterozygous
Mendelian Genetics
The genotype is the genetic makeup of an organism.
It is the coding of alleles the organism
For trait “T,” homozygous dominant is TT,
homozygous recessive is tt and heterozygous is Tt
The phenotype is the physical expression of the
gene. For trait “T” it would be taster or non-taster
Later, genes would be found inside chromosomes,
where the heredity material is passed to offspring
Genotypes
Phenotypes
Evolutionary Synthesis
Four mechanisms for evolution:
Mutation: a change in genetic information; adds
new genetic material; can be good/bad/neutral
Gene flow: organism’s migrate and mate with a
new group. The merging of new gene pools
creates variation
Genetic drift: when a group is small, some traits
are over-represented and some are underrepresented
Natural selection
Questions to ponder…
How can you describe natural selection in your own
terms? What are some examples?
How are Darwin’s and Lamarck’s theories similar and
different? Is one correct and one incorrect?
How did Mendel discover how traits are inherited?
What do his two principles show us?