Slides from a departmental seminar in UCLA's department of Ecology and Evolutionary Biology, January 6th 2016. The seminar was videotaped and should be available shortly online.

1. Anthropogenic evolution,
externalities, and public health
CarlT. Bergstrom
Department of Biology
University of Washington
Department of Ecology and Evolution, UCLA
January 6, 2016

2. MarkTanaka Ben Althouse Ted Bergstrom Marc Lipsitch
UNSW IDM USCB Harvard
Participants in the
2011 Heron
Island Summit on
Evolutionary
Challenges in
Food, Health, and
the Environment

3. Overview
Anthropogenic
evolution and
externalities.
Carroll et al (2014)
Science 346:313
Public choice
theory for
public health
Althouse et al (2010)
PNAS 107:1696
Timing of antiviral
use during a
pandemic
Tanaka et al (2014)
Evolution, Medicine, and
Public Health 2014:150
http://octavia.zoology.washington.edu

4. Anthropogenic evolution and externalities.
Carroll al (2014) Science 346:313

5. Herbicide resistance
Heap (2012) Online
Glyphosate (Roundup) resistant weeds

6. Antibiotic resistance
Bergstrom and Dugatkin (2016) Evolution 2nd ed.

7. Fisheries Induced Evolution
Borrell (2013) Nature

8. Harvesting Induced Evolution
Decreasing size
in harvested,
but not non-
harvested,
species of
snow lotus in
the Himalayas.
Law and Salick (2005) PNAS

9. Conservation captive breeding

10. Gene drive
Harvard Wyss Institute Gene Drive FAQ

11. In general, the problem with managing
anthropogenic evolution is that
The species we
want to evolve fast,
evolve slow,
And the species we
want to evolve slow,
evolve fast.
Images:
superbwallpapers.com,
free-­‐designer.net

12. Evolutionary changes in wild
populations generate externalities

13. What are externalities?
Economic side-effects that are
not captured by market prices.

14. Negative
externalities
Images:
Wikimedia

15. Many other situations with negative externalities involve
common-pool resources: they are non-excludable,
but rivalrous.The result in tragedies of the commons.

16. cc
by
flickr:bekhiann
Positive
externalities
cc
by
flickr:Brigit
Murphy

17. Meanwhile, pure public goods are non-excludable
and non-rivalrous. Creating these generates positive
externalities.
Private markets tend to under-allocate to pure public
goods. Governments need to intervene.
National Defense is
the example accepted
most broadly on both
sides of the political
aisle.
cfr.org

18. Evolutionary changes in wild
populations generate externalities
Harmful changes tend to be common pool issues.
• Non-excludable but rivalrous
• Hard to monitor, hard to attribute cause / blame
Beneficial changes tend to be pure public goods
• Non-excludable, non-rivalrous

19. How can we deal with externalities?
Economists have a rich toolkit
(and extensive theory, of course!)

20. Command
and control
policies
wikimedia

21. Sir Alexander Fleming,
Nobel Prize Lecture, 1945

22. wikimedia

23. (We need) Antibiotic regulation
Bergstrom and Dugatkin (2016) Evolution 2nd ed.

24. Tort Law
wikimedia

25. Aventis Starlink Corn
Images:
NCI,
wikimedia.

26. Establish property rights (cap and trade)
cc
flickr:Thomas
Berg

27. Catch shares for fisheries
wikimedia

28. Pigovian taxes
In Sweden, spirits are taxed €50 euro / liter

29. Pigovian subsidies
Poster:
Wikimedia

30. As evolutionary biologists we can
explain how human actions lead
to anthropogenic evolution
We would do well to understand the
the policy tools available for
modulating these actions.

31. Public choice theory for public health
Althouse et al (2010) PNAS 107:1696

32. When should the government
get involved in public health?
When it can improve the lives of the
most needy members of society.

33. On efficiency grounds, when
does government investment
in public health out-perform
private market solutions?

34. Public choice theory
SuscepEble Infected Removed
Epidemiological modeling
Paul Samuelson 1955

35. Tetanus
Measles
Otitis media
Pandemic Influenza

36. Tetanus

37. Tetanus occurs when the soil microbe
Clostridium tetani infects a deep wound.
It is not transmitted from human to human
Vaccine targets the toxin, not the microbe.

38. My tetanus vaccine doesn’t affect you,
positively or negatively.
It is a pure private good.
cc flickr: Penn State

39. Measles
Image: Helen Bergstrom, then age 6.

40. Images: kinderhelper.com
My problem
Your problem

41. Images: kinderhelper.com
Private good
Positive
externality

42. SuscepEble Infected Removed
Vaccinate fraction p

43. SuscepEble Infected Removed
Vaccinate fraction p
Infections decrease linearly with
fraction of the population vaccinated.

48. Optimal
Subsidy

49. €
v(q) − C'(qN) − kX(q) = 0
Direct value of
treating one individual
Cost of treating
one individual
Effect of treating one
person on all others.
First-order condition for social efficiency

50. v(q) − C'(qN) − k q
∂htreated (q)
∂q
+ (1− q)
∂huntreated (q)
∂q
$
%
'
(
) = 0
Direct value of
treating one individual
Cost of treating
one individual
Cost of one infection
Effect on other treated individuals
Effect on untreated individuals

51. €
s = −k q
∂htreated (q)
∂q
+ (1− q)
∂huntreated (q)
∂q
$
%
'
(
)
In our measles example, vaccination
affects untreated but not treated individuals
A Pigouvian subsidy of this magnitude
aligns private and public interest

52. Otitis media
wikimedia

53. Otitis media is caused Streptococcus
pneumonia and Haemophilus influenzae.
Half of preschool aged children carry
them asymptomatically.
Image: Dennis Kunkel

54. Otitis media occurs when these bacteria make
their way up the eustachian tube into the
tympanic cavity - and thus is rarely transmissible
from the infection site.
www.patienteducationcenter.org

55. American Academy of Pediatrics (2004)
Minimize use of antibiotics for uncomplicated
otitis media.
Use amoxicillin rather than a late generation
drug if antibiotics are necessary.

56. Patients vary in their
need for the drug
Otherwise healthy children
can easily clear the infection
without treatment.
Children suffering from
other complications may
need drug treatment

57. After Bonhoeffer et al. 1996
Steady-state resistance
increases with fraction
treated.

58. Marginal private benefit
Marginal public benefit
Marginal cost

59. Optimal
tax

60. €
s = −k q
∂htreated (q)
∂q
+ (1− q)
∂huntreated (q)
∂q
$
%
'
(
)
In our Otitis media example,
treatment affects other treated
individuals but not those who are untreated
A Pigouvian tax of this magnitude
aligns private and public interest

61. Pandemic Influenza
Images: http://www.coo.kz/

62. • Social distancing
• Vaccination
• Antivirals

63. Antivirals
Reduce mortality morbidity
Reduce transmission
Select for resistance
Private good
Positive externality
Negative externality

64. How should we distribute antivirals?
Flu Kits:
Families purchase in advance as insurance against
pandemic
Pharmacy distribution:
Doses are distributed to individuals once infected

65. After Lipsitch et al 2007

66. Flu kit scenario

67. Pharmacy distribution scenario

68. Timing of antiviral use during a pandemic
Tanaka et al (2014) Evolution, Medicine, and Public Health 2014:150

69. Staphylococcus aureus
Pseudomonas aeruginosa
Enterococcus sp.
Klebsiella pneumoniae

70. Surgical
ICU
central
line
catheter
infecEon
rates
Denver
Health
Quality
Report
2009

73. When should we deploy a limited stockpile
of antimicrobials to maximize benefits over
the course of an epidemic?

74. Direct benefits (private goods): reduction of
mortality and morbidity in treated
individuals.
Indirect benefits (externalities): changes in
the epidemic trajectory due to antimicrobial
use.

75. See
Handel,
Longini,
and
AnEa
(2007)
Proc
R.
Soc.
B
274:833-­‐837

76. See
Handel,
Longini,
and
AnEa
(2007)
Proc
R.
Soc.
B
274:833-­‐837

77. See
Handel,
Longini,
and
AnEa
(2007)
Proc
R.
Soc.
B
274:833-­‐837

78. See
Handel,
Longini,
and
AnEa
(2007)
Proc
R.
Soc.
B
274:833-­‐837

79. X
YSU
YST
YR
Z
θ
ν/(1-­‐ε)
ν
ν
1-­‐fξ
fξ

80. Treatment
start
Eme
(days)
FracEon
of
stockpile
used
successfully

82. Model results (≠policy suggestions)
Limited stockpile? Don’t use it right away.
Even with an unlimited stockpile, the total
social welfare is greatest when one delays
antimicrobial use some time into the epidemic.

83. Why ?

84. Indirect benefits come from reducing
overshoot by reducing transmission at and
beyond the epidemic threshold, i.e., late in the
epidemic, to minimize overshoot.

85. Direct benefits depend on the number
of treatment failures due to resistance.
Here timing is everything.

86. Direct benefits depend on the number
of treatment failures due to resistance.
Here timing is everything.

87. To summarize:
Early use generates negative
externalities by promoting the
evolution of antiviral resistance.
Late use creates positive externalities,
by reducing the overshoot of the
epidemic.
You might take this as an argument in favor
of delaying antiviral treatment until well into
an epidemic.

88. Generally not a good idea to delay antiviral use.
Delaying use
• may not be ethical
• prevents any chance of early eradication
• risks wasting doses if use begins too late

89. Correctly ordering the use of multiple drugs may
be feasible.
Compare
Wu
et
al.
2009
PLoS
Medicine

90. Summary
Anthropogenic evolution in wild populations has
profound costs—and benefits—for society.
But its consequences are diffuse and rarely captured
by economic markets.
We can manage anthropogenic evolution—but we
need the tools and theory from public choice
economics to implement effective policy.
This is our chance as evolutionary biologists to be
societally relevant. Let’s do this!

91. MarkTanaka Ben Althouse Ted Bergstrom Marc Lipsitch
UNSW IDM USCB Harvard
Participants in the
2011 Heron
Island Summit on
Evolutionary
Challenges in
Food, Health, and
the Environment