Legacies Flashcards
does natural selection produce “perfect” organisms
- no
what are some reasons that natural selection may produce “imperfect” individuals/limitations of NS (5)
- historical legacies or path dependency
- lack of variation
- time lags
- trade-offs
- genetic drift
limitations of NS: historical legacies (2)
- natural selection acts to modify existing features; thus, organisms are constrained by their evolutionary history
- natural selection is a “tinkerer” not an “engineer”
limitations of NS: examples of historical legacies (3)
- panda’s thumb
- upper respiratory tract of mammals
- human childbirth
limitations of NS: historical legacies
- panda’s thumb
- panda’s thumb is not a digit, but a modified wrist bone
limitations of NS: historical legacies (2)
- upper respiratory tract of mammals
- we choke easily due to crossing on respiratory and digestive tract
- due to fish ancestry: lungfish ancestor had lungs used occasionally that crossed with the digestive tract
limitations of NS: historical legacies
- human childbirth (2)
- large brains, bipedality, and egg-laying ancestors of humans push the envelope of evolution
- human childbirth is very difficult because human babies can barely make it through the birth canal
simplified phylogeny of tetrapods (4)
- hard-shelled amniotic egg
- viviparity: giving birth to live offspring
- well-developed placenta
- bipedality and large brains
limitations of NS: lack of variation
- natural selection depends on existence of appropriate variants, which arise through mutations, a process RANDOM with respect to the direction of evolution
limitations of NS: examples of lack of variation (2)
- disease emergence
- beetle adaptations to novel host plants
limitations of NS: lack of variation
- disease emergence
- new variants needed for disease emergence (mutations that allow for fitness valleys to occur)
limitations of NS: lack of variation
- beetle host adaptations
- beetle species lack genetic variability to shift to phylogenetically distant host plant species
limitations of NS: time lags (2)
- organisms typically lag behind their environment: the are adapted to conditions in their immediate past, not their future
- red queen hypothesis: organisms are “running” to keep up with environment through NS, but always stay behind environmental changes
limitations of NS: examples of time lags (4)
- myopia
- type II diabetes
- lactose malabsorption
- allergies and autoimmune disorders
limitations of NS: time lags
- type II diabetes
- it is very common in populations exposed to feast and famine: ‘thrifty genotype’ hypothesis
thrifty genotype
- populations exposed to feast and famine had maximum metabolic efficiency
- fat deposition at times of plenty and survival at times if famine
examples of thrifty gene phenotypes
- replenish skeletal muscle
- store glucose and TG in adipose tissue
thrifty genotype stages (3)
PHYSICAL ACTIVITY (hunt or gather) 1. feast: intake of glucose and fat RELATIVE PHYSICAL INACTIVITY 2. thrifty storage: - replenish skeletal muscle - store glucose and TG in adipose tissue MORE THRIFTY = MORE LIKELY TO SURVIVE FAMINE 3. famine & activity: - decrease glycogen and TG stores CONTRACTING SKELETAL MUSCLE
what changes are made to the ‘thrifty’ genotype in modern lifestyles (3)
- feast: unlimited food supply with no exercise; skeletal muscle & TG stores NOT decreased
- thrifty storage: fuel is shunted into greater and unhealthy stores (metabolic syndrome)
- no famine & activity phase
what are the results of the ‘thrifty genotype’ in the modern lifestyle (3)
- obesity
- type II diabetes
- cardio vascular disease
‘thrifty genotype’ hypothesis (2)
- populations exposed the longest to modern life style (Europeans) may have (partially) weeded out ‘thrifty genes’ as those susceptible in environment died/had lower fitness
- most of humanity is poorly adapted (at least, metabolically) to our modern lifestyle
metabolic syndrome
- type II diabetes
- obesity
- cardio vascular diabetes
thrift phenotype hypothesis
- metabolic programming due to malnutrition during fetal development may lead to metabolic syndrome when there is excess food later in life
drifty genotype hypothesis
- released from heavy predation, genetic drift led to accumulation of mutations that cause diabetes/obesity
lactase
- enzyme necessary for digesting of lactose, a protein abundant in milk
lactose intolerance (2)
- lactase production switches off during infancy in most mammals and people
- many of us are unable to digest lactose as adults
lactase persistence
- in some human populations, gene controlling lactase production mutated so lactase production is not switched off
hypotheses of lactose malabsorption (3)
- to take advantage of easy supply of milk from herds of pastoral animals
- promotion of calcium uptake in high latitude populations prone to vitamin D deficiency
- to use milk as alternative source of water, where water is scarce
what hypothesis of lactose malabsorption is correct?
- phylogenetic methods show that lactase persistence is associated with pastoralism, not with aridity or solar radiations
potential issue of testing lactose malabsorption theories
- ethnic non-independence when comparing between different ethnicities of people
limitations of NS: trade-offs
- selection acts on different aspects of the life cycle of individuals: features favoured at one stage may be disfavoured at others
limitations of NS: trade-offs
- stages and aspects NS can act on (4)
- adult -> mating pairs: sexual selection
- mating pairs -> gametes: fecundity
- gametes -> zygote: gametic selection
- zygote -> adult: viability
limitations of NS: trade-offs
- examples (2)
- natural selection vs sexual selection
2. longevity vs fertility
are all features of organisms adaptive?
- no, some may result from laws of physics or chemistry
- might be shaped by chance (drift)
does NS lead to high complexity
- no
can the course of evolution be predicted
- no
