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A Tale of Three Lice
Joan Sharp and Erin Barley
Simon Fraser University
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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
Limitations of the Fossil Record
But there are questions about hominins that the
fossil record cannot answer:
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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
Can lice help?
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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 body louse,
Pediculus humanus corporis
The pubic louse,
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
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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.
How would you test this hypothesis?
Human Chimp
Gorilla Orangutan Gibbon
Old world monkey
million years ago
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
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The last common ancestor of chimp lice and human head lice lived approximately:
A. 20 million years ago, on an early ape ancestor.
B. 6 million years ago, when ancestral chimps and hominins diverged.
C. 100,000 years ago, on an early human.
CQ#1: What would you predict, given the
co-speciation hypothesis?
Human Chimp Gorilla Orangutan GibbonOld world monkey
million years ago
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:
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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.
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.
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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.
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.
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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.
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.
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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
Phylogeny of selected primates & their lice
Head 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.
The origin of pubic lice
• Surprise! Human pubic lice (Phthirus pubis) belong to the same genus as gorilla lice
(Phthirus gorillae).
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Hmmm…
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.
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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…
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.
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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.
A possible origin of body lice
Third niche hypothesis:
• Human body lice arose because humans started to wear clothing.
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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.
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.
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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?
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
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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.
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
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.
