A Tale of Three Lice
Joan Sharp and Erin Barley
Simon Fraser University
1
Fossil Record and Ape Speciation
Fossils provide
information
about shared
ancestry and
relationships
among taxa.
2
Hominins
• The human lineage and the chimp lineage
diverged ~6 million years ago.
• Homo sapiens evolved ~200,000 years
ago and were preceded by several other
species of hominin.
• A hominin is any species that is more
closely related to a human than a
chimpanzee (e.g., members of the genera
Australopithecus and Homo).
3
Limitations of the Fossil Record
But there are questions about hominins that the
fossil record cannot answer:
– When did hominins lose their body hair?
– When did hominins begin to wear clothes?
4
How can we answer these
questions?
• Examine patterns of hominin distribution and
past climate maps
– This might be helpful, but won’t provide direct
evidence
• Look for tools used to make clothes
– The oldest needles are ~40,000 years old, but only
provide a minimum age for clothing
• It’s like looking for a needle in all the haystacks of Europe!
5
Can lice help?
• Can lice tell us when hominins lost their
body hair and/or started wearing clothing?
6
A tale of three lice
• Lice are highly specialized blood sucking
parasites that live on a single host species.
• Each of our ape relatives hosts one louse species,
but humans host three types of lice.
The head louse,
Pediculus humanus
capitus
The pubic louse,
Phthirus pubis
The body louse,
Pediculus humanus
corporis
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The origin of head lice
• Human head lice and chimp lice belong to
the same genus. Why did these two
lineages of lice diverge?
• Working in pairs, think of 1 or 2
hypotheses, and write them down.
8
A possible origin of head lice
Co-speciation hypothesis:
– Human head and chimp lice lineages diverged at the
same time that hominins and ancestral chimps diverged.
Human
Chimp
Gorilla
Orangutan
Gibbon
Old world monkey
30
25
20
15
10
5
0
million years ago
How would you test this hypothesis?
9
The origin of head lice
Co-speciation hypothesis:
– Human head and chimp lice lineages diverged
at the same time that hominins and ancestral
chimps diverged.
To test this hypothesis:
– Compare DNA of human head lice to DNA of
chimp lice at one nuclear and one mitochondrial
gene to estimate when they last shared a
common ancestor.
10
CQ#1: What would you predict, given the
co-speciation hypothesis?
The last common ancestor of chimp lice and human head lice lived
approximately:
A.
B.
C.
20 million years ago, on an early ape ancestor.
6 million years ago, when ancestral chimps and hominins
diverged.
100,000 years ago, on an early human.
Human
Chimp
Gorilla
Orangutan
Gibbon
Old world monkey
30
25
20
15
10
million years ago
5
0
11
The origin of head lice
Prediction:
• The last common ancestor of chimp lice and human
head lice lived ~6 million years ago.
Results:
• A DNA comparison suggests the most recent common
ancestor of chimp lice and human head lice lived ~6
million years ago.
Conclusion:
• Hominins and their head lice co-speciated from ancestral
chimps and their lice.
12
The origin of pubic lice
• Consider human head lice and pubic lice.
Why did these two lineages of lice
diverge?
• Working in pairs, think of 1 or 2
hypotheses, and write them down.
13
A possible origin of
pubic lice
New niche hypothesis:
– Human pubic and head lice lineages diverged
because hominins lost their body hair and
developed two hair niches.
How would you test this hypothesis?
14
The origin of pubic lice
New niche hypothesis:
– Human pubic and head lice lineages diverged
because hominins lost their body hair and
developed two hair niches.
To test this hypothesis:
– First, compare DNA of human pubic lice to
human head lice at one nuclear and one
mitochondrial gene to estimate when they last
shared a common ancestor.
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CQ#2: What would you predict, given
the new niche hypothesis?
Human head and pubic lice lineages diverged
from a common ancestor approximately:
A. 25 million years ago, when ape and monkey
lineages split.
B. 6 million years ago, when human and chimp
lineages split.
C. 6 million years ago or less, on a hominin
host.
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The origin of pubic lice
Prediction:
• Human head and pubic lice lineages diverged from a
common ancestor less than 6 million years ago, on a
hominin host.
Results:
• DNA comparison suggests the most recent common
ancestor of human head lice and human pubic lice lived
~12 million years ago.
Conclusion:
• Human head and pubic lice did not diverge on a
hominin.
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CQ#3: Why do we conclude that human
head and pubic lice did not diverge
on a hominin?
A. Human head and pubic lice lineages diverged
well before hominins evolved ~6 million years
ago.
B. Humans had body hair well after 12 million
years ago.
C. The fossil record does not show pubic lice on
people that long ago.
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The origin of pubic lice
• Use the phylogenetic tree on the next
page to answer the following question:
– Given the phylogeny of select primates and
their lice, what is the most likely origin of
human pubic lice?
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Phylogeny of selected primates & their lice
Head lice
Pubic lice
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CQ#4: Given the phylogeny of select
primates and their lice, what is the
closest relative of human pubic lice?
A. Human pubic lice are most closely related to
chimp lice.
B. Human pubic lice are most closely related to
gorilla lice.
C. Human pubic lice are most closely related to
human head lice.
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The origin of pubic lice
• Surprise! Human pubic lice (Phthirus pubis)
belong to the same genus as gorilla lice
(Phthirus gorillae).
• DNA comparisons show that human pubic lice
and gorilla lice last shared a common ancestor
3-4 million years ago.
22
Hmmm…
• What were the Australopithecines and
early gorillas up to?
23
The origin of pubic lice
• Hominins might have picked up lice from
early gorillas by:
– Sleeping in nests recently used by early
gorillas.
– Preying on early gorillas.
• Lice are known to jump from prey to predator.
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The origin of pubic lice
• Why were the lice of early gorillas able to
colonize hominins?
– One possible explanation is that hominins had
lost much of their body hair and so had two
“hair niches.”
– This explanation is still highly speculative.
– Research continues…
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The origin of body lice
• Human head and body lice are different
morphotypes belonging to the same species.
• Human body lice live on clothing and move onto
skin up to 5 times a day to feed.
The head louse,
Pediculus humanus
capitus
The body louse,
Pediculus humanus
corporis
26
The origin of body lice
• Consider now human head lice and body
lice. Why did body lice arise?
• Working in pairs, think of a hypothesis,
and write it down.
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A possible origin of body lice
Third niche hypothesis:
• Human body lice arose because humans started
to wear clothing.
How would you test this hypothesis?
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The origin of body lice
Third niche hypothesis:
• Human body lice arose because humans
started to wear clothing.
To test this hypothesis:
• First, estimate when body lice arose by
identifying the most recent common
ancestor of all body lice.
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CQ#5: What would you predict, given the
third niche hypothesis?
The last common ancestor of human head and
body lice lived:
A. Approximately 6 million years ago, on the
common ancestor of humans and chimps.
B. 1-2 million years ago, on a hominin that had
lost some or all of its body hair.
C. Less than 100,000 years ago, on a modern
human.
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The origin of body lice
Prediction:
• The last common ancestor of human head lice and
human body lice lived less than 100,000 years ago.
Results:
• A DNA comparison suggests the most recent common
ancestor of human body lice lived less than 72,000 years
ago.
Conclusion:
• Human body lice arose from human head lice on Homo
sapiens.
• These data suggest that clothing might have arisen
~72,000 years ago.
• Are these data also consistent with other hypotheses?
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In summary
• Phylogenetic studies of lice suggest that:
– Hominins acquired a second species of louse
~3-4 million years ago.
• Does this correlate with the loss of body hair?
– Body lice arose less than 72,000 years ago.
• Does this correlate with the development of
clothing?
• These studies provide interesting and
relevant data, but more data are needed
before we can answer these questions.
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In summary
• When did hominins lose their body hair
and/or start wearing clothing?
– These questions remain unanswered, though
lice provide some interesting and relevant
data.
– Answers to these questions will likely depend
on data from multiple sources, including lice.
Research continues… but don’t forget:
Never share your hairbrush!
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Slide Credits
Slide 1—Left, Slide 6, Slide 7—Left, Slide 26—Left, Slide 33
Description: Human head louse, Pediculus humanus capitus.
Source: Figure 1 from Reed, D.L., Light, J.E., Allen, J.M., Kirchman, J.J. 2007. Pair of lice lost or
parasites regained: The evolutionary history of anthropoid primate lice. BioMedCentral
Biology 5:7, page 3.
Permissions: Creative Commons Attribution 2.5 License.
Slide 1—Center, Slide 7—Center
Description: Human pubic louse, Pthirus pubis.
Source: Figure 1 from Reed, D.L., Light, J.E., Allen, J.M., Kirchman, J.J. 2007. Pair of lice lost or
parasites regained: The evolutionary history of anthropoid primate lice. BioMedCentral
Biology 5:7, page 3.
Permissions: Creative Commons Attribution 2.5 License.
Slide 1—Right, Slide 7—Right, Slide 26—Right
Description: Human body (clothing) louse, Pediculus humanus corporus.
Source: CDC / Dr. Dennis D. Juranek, http://phil.cdc.gov/phil/home.asp
Permissions: This image is a work of the Centers for Disease Control and Prevention, part of the
United States Department of Health and Human Services, taken or made during the course
of an employee’s official duties. As a work of the U.S. federal government, the image is in the
public domain.
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Slide 4—Left
Description: Photograph of chimpanzee.
Author: Thomas Lersch.
Source: Wikimedia, http://commons.wikimedia.org/wiki/File:Schimpanse_zoo-leipig.jpg
Permissions: Creative Commons Attribution 2.5 License.
Slide 4 —Right
Description: Photograph of shirtless male (Landon Donovan).
Author: Linny Heng
Source: Wikimedia, http://commons.wikimedia.org/wiki/File:Landon_Donovan_shirtless.jpg
Permissions: Creative Commons Attribution 2.0 License.
Slide 20
Description: Phylogenetic tree for primate lice and their vertebrate hosts.
Source: Figure 1 from Reed, D.L., Light, J.E., Allen, J.M., Kirchman, J.J. 2007. Pair of lice lost or
parasites regained: The evolutionary history of anthropoid primate lice. BioMedCentral Biology
5:7, page 3.
Permissions: Creative Commons Attribution 2.5 License.
Slide 23
Description: Genetic reconstruction of lice and host phylogeny.
Source: Figure 2 from Reed, D.L., Light, J.E., Allen, J.M., Kirchman, J.J. 2007. Pair of lice lost or
parasites regained: The evolutionary history of anthropoid primate lice. BioMedCentral Biology
5:7, page 4.
Permissions: Creative Commons Attribution 2.5 License.
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