Legacies Flashcards
1
Q
does natural selection produce “perfect” organisms
A
- no
2
Q
what are some reasons that natural selection may produce “imperfect” individuals/limitations of NS (5)
A
- historical legacies or path dependency
- lack of variation
- time lags
- trade-offs
- genetic drift
3
Q
limitations of NS: historical legacies (2)
A
- natural selection acts to modify existing features; thus, organisms are constrained by their evolutionary history
- natural selection is a “tinkerer” not an “engineer”
4
Q
limitations of NS: examples of historical legacies (3)
A
- panda’s thumb
- upper respiratory tract of mammals
- human childbirth
5
Q
limitations of NS: historical legacies
- panda’s thumb
A
- panda’s thumb is not a digit, but a modified wrist bone
6
Q
limitations of NS: historical legacies (2)
- upper respiratory tract of mammals
A
- 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
7
Q
limitations of NS: historical legacies
- human childbirth (2)
A
- 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
8
Q
simplified phylogeny of tetrapods (4)
A
- hard-shelled amniotic egg
- viviparity: giving birth to live offspring
- well-developed placenta
- bipedality and large brains
9
Q
limitations of NS: lack of variation
A
- natural selection depends on existence of appropriate variants, which arise through mutations, a process RANDOM with respect to the direction of evolution
10
Q
limitations of NS: examples of lack of variation (2)
A
- disease emergence
- beetle adaptations to novel host plants
11
Q
limitations of NS: lack of variation
- disease emergence
A
- new variants needed for disease emergence (mutations that allow for fitness valleys to occur)
12
Q
limitations of NS: lack of variation
- beetle host adaptations
A
- beetle species lack genetic variability to shift to phylogenetically distant host plant species
13
Q
limitations of NS: time lags (2)
A
- 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
14
Q
limitations of NS: examples of time lags (4)
A
- myopia
- type II diabetes
- lactose malabsorption
- allergies and autoimmune disorders
15
Q
limitations of NS: time lags
- type II diabetes
A
- it is very common in populations exposed to feast and famine: ‘thrifty genotype’ hypothesis
16
Q
thrifty genotype
A
- populations exposed to feast and famine had maximum metabolic efficiency
- fat deposition at times of plenty and survival at times if famine
17
Q
examples of thrifty gene phenotypes
A
- replenish skeletal muscle
- store glucose and TG in adipose tissue
18
Q
thrifty genotype stages (3)
A
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
19
Q
what changes are made to the ‘thrifty’ genotype in modern lifestyles (3)
A
- 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
20
Q
what are the results of the ‘thrifty genotype’ in the modern lifestyle (3)
A
- obesity
- type II diabetes
- cardio vascular disease
21
Q
‘thrifty genotype’ hypothesis (2)
A
- 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
22
Q
metabolic syndrome
A
- type II diabetes
- obesity
- cardio vascular diabetes
23
Q
thrift phenotype hypothesis
A
- metabolic programming due to malnutrition during fetal development may lead to metabolic syndrome when there is excess food later in life
24
Q
drifty genotype hypothesis
A
- released from heavy predation, genetic drift led to accumulation of mutations that cause diabetes/obesity
25
lactase
- enzyme necessary for digesting of lactose, a protein abundant in milk
26
lactose intolerance (2)
- lactase production switches off during infancy in most mammals and people
- many of us are unable to digest lactose as adults
27
lactase persistence
- in some human populations, gene controlling lactase production mutated so lactase production is not switched off
28
hypotheses of lactose malabsorption (3)
1. to take advantage of easy supply of milk from herds of pastoral animals
2. promotion of calcium uptake in high latitude populations prone to vitamin D deficiency
3. to use milk as alternative source of water, where water is scarce
29
what hypothesis of lactose malabsorption is correct?
- phylogenetic methods show that lactase persistence is associated with pastoralism, not with aridity or solar radiations
30
potential issue of testing lactose malabsorption theories
- ethnic non-independence when comparing between different ethnicities of people
31
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
32
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
33
limitations of NS: trade-offs
| - examples (2)
1. natural selection vs sexual selection
| 2. longevity vs fertility
34
are all features of organisms adaptive?
- no, some may result from laws of physics or chemistry
| - might be shaped by chance (drift)
35
does NS lead to high complexity
- no
36
can the course of evolution be predicted
- no
