Legacies

Question 1

does natural selection produce “perfect” organisms

Answer 1

• no

Question 2

what are some reasons that natural selection may produce “imperfect” individuals/limitations of NS (5)

Answer 2

• historical legacies or path dependency
• lack of variation
• time lags
• trade-offs
• genetic drift

Question 3

limitations of NS: historical legacies (2)

Answer 3

• natural selection acts to modify existing features; thus, organisms are constrained by their evolutionary history
• natural selection is a “tinkerer” not an “engineer”

Question 4

limitations of NS: examples of historical legacies (3)

Answer 4

• panda’s thumb
• upper respiratory tract of mammals
• human childbirth

Question 5

limitations of NS: historical legacies

- panda’s thumb

Answer 5

• panda’s thumb is not a digit, but a modified wrist bone

Question 6

limitations of NS: historical legacies (2)

- upper respiratory tract of mammals

Answer 6

• 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

Question 7

limitations of NS: historical legacies

- human childbirth (2)

Answer 7

• 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

Question 8

simplified phylogeny of tetrapods (4)

Answer 8

1. hard-shelled amniotic egg
2. viviparity: giving birth to live offspring
3. well-developed placenta
4. bipedality and large brains

Question 9

limitations of NS: lack of variation

Answer 9

• natural selection depends on existence of appropriate variants, which arise through mutations, a process RANDOM with respect to the direction of evolution

Question 10

limitations of NS: examples of lack of variation (2)

Answer 10

• disease emergence

- beetle adaptations to novel host plants

Question 11

limitations of NS: lack of variation

- disease emergence

Answer 11

• new variants needed for disease emergence (mutations that allow for fitness valleys to occur)

Question 12

limitations of NS: lack of variation

- beetle host adaptations

Answer 12

• beetle species lack genetic variability to shift to phylogenetically distant host plant species

Question 13

limitations of NS: time lags (2)

Answer 13

• 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

Question 14

limitations of NS: examples of time lags (4)

Answer 14

• myopia
• type II diabetes
• lactose malabsorption
• allergies and autoimmune disorders

Question 15

limitations of NS: time lags

- type II diabetes

Answer 15

• it is very common in populations exposed to feast and famine: ‘thrifty genotype’ hypothesis

Question 16

thrifty genotype

Answer 16

• populations exposed to feast and famine had maximum metabolic efficiency
• fat deposition at times of plenty and survival at times if famine

Question 17

examples of thrifty gene phenotypes

Answer 17

• replenish skeletal muscle

- store glucose and TG in adipose tissue

Question 18

thrifty genotype stages (3)

Answer 18

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

Question 19

what changes are made to the ‘thrifty’ genotype in modern lifestyles (3)

Answer 19

• 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

Question 20

what are the results of the ‘thrifty genotype’ in the modern lifestyle (3)

Answer 20

• obesity
• type II diabetes
• cardio vascular disease

Question 21

‘thrifty genotype’ hypothesis (2)

Answer 21

• 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

Question 22

metabolic syndrome

Answer 22

• type II diabetes
• obesity
• cardio vascular diabetes

Question 23

thrift phenotype hypothesis

Answer 23

• metabolic programming due to malnutrition during fetal development may lead to metabolic syndrome when there is excess food later in life

Question 24

drifty genotype hypothesis

Answer 24

• released from heavy predation, genetic drift led to accumulation of mutations that cause diabetes/obesity

Question 25

lactase

Answer 25

- enzyme necessary for digesting of lactose, a protein abundant in milk

Question 26

lactose intolerance (2)

Answer 26

- lactase production switches off during infancy in most mammals and people - many of us are unable to digest lactose as adults

Question 27

lactase persistence

Answer 27

- in some human populations, gene controlling lactase production mutated so lactase production is not switched off

Question 28

hypotheses of lactose malabsorption (3)

Answer 28

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

Question 29

what hypothesis of lactose malabsorption is correct?

Answer 29

- phylogenetic methods show that lactase persistence is associated with pastoralism, not with aridity or solar radiations

Question 30

potential issue of testing lactose malabsorption theories

Answer 30

- ethnic non-independence when comparing between different ethnicities of people

Question 31

limitations of NS: trade-offs

Answer 31

- selection acts on different aspects of the life cycle of individuals: features favoured at one stage may be disfavoured at others

Question 32

limitations of NS: trade-offs | - stages and aspects NS can act on (4)

Answer 32

- adult -> mating pairs: sexual selection - mating pairs -> gametes: fecundity - gametes -> zygote: gametic selection - zygote -> adult: viability

Question 33

limitations of NS: trade-offs | - examples (2)

Answer 33

1. natural selection vs sexual selection | 2. longevity vs fertility

Question 34

are all features of organisms adaptive?

Answer 34

- no, some may result from laws of physics or chemistry | - might be shaped by chance (drift)

Question 35

does NS lead to high complexity

Answer 35

- no

Question 36

can the course of evolution be predicted

Answer 36

- no