Ultimate Flashcard Extravaganza
Evolution Before Charles Darwin
Enlightenment - no divine right to rule, natural phenomena are mechanically caused by external forces
Erasmus Darwin - Charles’ grandfather, organisms’ sensitivity to the environment shapes their minds and bodies, better forms have increased over time
Jean-Baptiste Lamarck
Jean-Baptiste Lamarck
- animals have an internal drive to physically accommodate to environmental conditions and become more complex
- persistently successful accommodations can become so habitual that they become physiologically based and get passed on to offspring
3 Influences of Darwin’s Theory
Charles Lyell (geologist) Thomas Malthus (economist/demographer) Alfred Russell Wallace (naturalist)
Charles Lyell
geologist, friend of Darwin
argued for a very slow and incremental pace of geological change
Thomas Malthus
economist and demographer
emphasized danger of uncontrolled human reproduction with limited resources
helped Darwin see the role of resource competition
Alfred Russell Wallace
independently discovered the theory of natural selection; letter prompted Darwin to submit their theories together in 1859
“Survival of the Fittest”
“fitness” is really “fittedness” - term was coined by Herbert Spencer, not Darwin
fitness is not determined by health or strength, but by reproductive success and ability to adapt to environment
3 dimensions of biological analysis
length - longitudinal analysis (homology)
breadth - comparative analysis (analogy)
depth - functional analysis (physiology)
How nature “backs up” her data
- Things naturally tend to fall apart and complicated mechanisms tend to wear out and fail
- One defense is to make copies
- Copying is never perfect - variation is inevitable
- Copying takes time and energy
- Some copying processes will be more profligate or successful than others
- Favored copying processes will be ones that best “fit” the conditions
Herbert Spencer
coined the phrase “survival of the fittest”
argued that evolution argued by Lamarckian use-inheritance
believed that learned habits could be passed on by reproduction –> social progress could lead to biological progress
argued that “primitive” societies were less evolved “races”
Haeckel and Progress
argued that evolution tends toward greater complexity
humans were presumed to occupy the highest rung on the biological ladder and were “the most evolved”`
Why Evolutionary Misconceptions are Wrong
Evolution is not linear and not necessarily progressive.
Its tendency is to diversify and expand into novel niches.
Evolution spontaneously tends toward increasing complexity because there is nowhere else to go.
“Planet of the Apes” Fallacy
nothing about natural selection produces inevitable trends, even improvement
humans didn’t replace or improve upon apes
Types of Selection
stabilizing selection - selection against extreme phenotypes that deviate from the mean
directional selection - selection favors extremes
disruptive selection - either extreme is favored
eg Japanese pheasants
The Red Queen analogy
the environment is always a moving target
it can look like there is an “arms race” between organisms adapting to the same environment, but they are just trying to keep up with the same changing environment
sometimes you have to run fast just to stay where you are
Mendel’s Basic Discovery
simple traits are controlled by an interaction between the two “doses” of each gene type (allele) that are present in each plant
because of this, they can interact or mask each other’s effects (dominant/recessive)
independently assort in subsequent generation according to simple binomial rule
Protein Functions
catalysts - aid chemical reactions, eg digestive enzymes
structural elements - or link other molecules, eg skin and hair
recognition or signaling - for cell cell communication
molecular “chaperones” - for other molecules that bind or transport eg hormone receptors and hemoglobin oxygen transport
SNPs
single nucleotide polymorphisms; different people can have different bases in a specific location
can be used for identification, diagnosis, and tracing ancestry
Genetic “drift”
statistical sampling effects producing random selection
there is always a 50% loss in genes from each parent
sex leads to inevitable gene elimination by chance
Founder Effect
a small group initially founds a population and diversifies from there
reduces genetic diversity
Why shift to a genetic perspective?
all bodies eventually perish! what persists are the genes that contribute to those traits
but: the particular combination of genes and traits that constitute an individual will likely never recur, except for in identical twins and asexual species
eg. Secretariat effect
Sickle Cell Anemia
sickle cell is only produced by the genetic mutation if both hemoglobin A molecules are sick type
hetereozygotes have 50% hemoglobin beta exhibiting mutation, which does not cause anemia but a low level of cell damage
this is sufficient to expose the malaria parasite to the immune system and help eliminate it
so: sickle cell heterozygotes are positively selected for
balanced polymorphism
Mitochondrial DNA
not contained within the cell nucleus but within the organelle
mitochondria are passed on in the cytoplasm of the ovum and therefore come only from the mother
mtDNA has bacterial origin!
(Y chromosome DNA is similar - only passed through male lineage)
Y chromosome inheritance
long arm of the Y chromosome does not recombine in sexual reproduction
inherited intact from father to son
therefore transmitted in all or none fashion and can be traced from individual to individual