Midterm Flashcards
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
gene duplication –> functional divergence
eg hemoglobin:
spontaneous degradation of duplicate genes produced beta-hemoglobin variants with different oxygen affinities
problem of transferring oxygen from maternal to fetal hemoglobin provides “functional niches” that variant hemoglobins can fit
Regulatory Genes
produce proteins that control patterns of gene expression in the different cells of a body
Extended Phenotype
selectively favored effects are expressed outside the body that produces them
genes can produce molecules whose primary focus is to control another species’ development or behavior
Death as a Reproductive Strategy
trade-off point between maintaining a body and instead putting that energy into reproduction is different for different species/life stages
salmon kill themselves in an effort to arrive upstream ahead of competitors and produce hundreds of offspring
mantis males easier to be caught and eaten late in the breeding season when chances of reproducing are slim and nutrition from eating their bodies could aid female reproduction
Sex has evolutionary costs
- only a random half of one’s genome gets passed to each offspring, and some genes don’t get passed on
- good gene combinations tend to get broken-up in each generation (Secretariat effect)
- time and resources are required to locate a mate, and often in fighting for mates
- probability of encountering a potential mate is reduced by 50%
- males use up resources and don’t contribute to offspring nourishment and health
Sex requires social interaction
- over the course of evolution, sexual reproduction has played the dominant role in promoting social behavior and cooperative organization within a species
- by distributing mutually exclusive reproductive adaptations among different individuals the advantages and disadvantages of each are separated
- traded off against the costs of making autonomous reproduction impossible, resulting in different combinations of sexual traits
sexual reproduction involves a mix of:
- Recombination (genes)
- Anisogamy (sperm and ova)
- Gender (male and female)
Why recombination?
genes must work in combination with one another
necessary to have them linked to keep working combinations together during reproduction
but this risks having a damaged gene ruin the reproductive chances of any linked gene
periodic recombination (shuffling) allows genes to escape linkage with “bad” genes
Anisogamy
“not the same gametes”
different gamete phenotypes: usually haploid, as in ova and sperm
sperm selected for: high numbers, low production costs, easy dispersal, high genetic diversity –> small, mobile, expendable
ova selected for: robustness, ample metabolic resources –> large, immobile, easily protected
Hermaphroditism
(both kinds of gametes) requires a compromise with respect to gender-distinct bodies where both dispersal-variation and investment-protection can be independently maximized
usually in conditions where access to mates is reduced
Sex vs. Body Gender
sex - typically understood in terms of male and female, used to refer to either whole animal bodies or to the organs of reproductions in plants that carry sperm (pollen) or ova (egg cells)
gender - linguistic designation of nouns and pronouns typically into masculine, feminine, and neuter grammatical types; has come to be used by analogical extension to refer to masculine vs feminine “roles” aka GENDER IS A SOCIAL CONSTRUCT
Conditions that Favor Asexual Reproduction
minimal competition for resource
predictable conditions
higher reproductive rate, lower variation
Conditions that Favor Sexual Reproduction
significant competition for resources
unpredictable conditions
lower reproductive rate, higher variation
Blue-Headed Wrasse
sex change
all begin life as females
live in a school defended by a single male, who is much larger on average, has a distinct blue head, and inseminates all eggs of the school
if this male dies, the larger females will compete and one will transform into a male developing a blue head
Anemonefish
“clownfish”
have an ability to prevent anemones from stinging them
pairs “nest” in an anemone where they raise young who can feed off prey paralyzed by anemone
begin life as males capable of producing sperm
young males pair up with older females who have successfully defended an anemone “nest site” in which to raise the young
older female dies, younger male undergoes a sex change to become a female and gonads begin to produce ova
young males will be attracted to mate with female
Darwin’s Theory of Sexual Selection
explains the evolution of apparently nonfunctional, superfluous, or harmful traits including human intelligence
emphasizes Darwin’s focus on reproduction
basic logic - reproductive competition not only dissociates members of a species into distinct sexes, but can lead to competition within the same sex for access to reproduction
Darwinian Logic of Sexual Selection
- better reproduction is more important than optimizing survival or access to resources
- there are often major differences in an individual’s reproductive output
- possibility of increasing reproduction could lead to competition for mates
- traits that trade health and survival for reproductive advantages will evolve where not blocked by natural selection
