Download Do humans still evolve?

Do humans still evolve?
• Evidence for recent evolution
in Homo sapiens
• Factors that influence rates
of evolution in Homo sapiens
• Cultural evolution
Mechanisms of Non-adaptive Evolution
• Mutation
Alteration of DNA during or after synthesis
• Genetic Drift
Loss of alleles due to random processes
• Natural Selection
Differential reproduction of heritable phenotypes
Recent Evolution of Homo sapiens
• Genetic evidence
• Phenotypic evidence
Genetic Legacy of Genghis Khan
● Many asian men share
the same Y-chromosome
● The highest frequency
occurs in Mongolia
Why did human skin become so diverse?
1) Losing hair solved problem of overheating on warming
savannas, but raised a new problem: exposure or UV radiation.
2) Darker skin, caused by production of melanin, prevents UV from
reaching sensitive cells.
UV radiation is a mixed blessing.
Positive:
-Vitamin D synthesis (this vitamin tells the gut to
absorb calcium; indispensable for skeletal and
immune systems)
Negative:
-Skin cancer (light-skinned people have 10x the risk
of dying of skin cancer under equal solar radiation).
-Causes breakdown of folic acid (a chemical needed
for DNA synthesis).
Jablonski & Chaplin 2000. The evolution of skin coloration. J. Human Evolution 39: 57-106
Zone 1
Zone 2
Zone 3
[Source: Jablonski & Chaplin 2000, J. Human Evolution 39: 57-106]
Less UV
Zone 1
Lighter
skin
Skin reflectance = Mean UV (-0.11) + 73
Zone 2
Zone 3
[Source: Jablonski & Chaplin 2000, J. Human Evolution 39: 57-106]
Repeated Evolution of Light Skin in
Northern Climates
• Genes that cause light skin in European and
Asian people are different
• Convergent evolution of skin color occurred
after emigration of humans from Africa.
• Suggests light skin arose via natural selection
and not genetic drift.
[Source: Norton et al. 2006, Genetic Evidence for the Convergent Evolution of Light
Skin in Europeans and East Asians. Molecular Biology & Evolution]
Genetic Drift of Facial Features
Australopithecus
Homo
[Source: Ackerman & Cheverud 2004, PNAS 101: 17946-17951]
About 90% of current variation in head shape
exists within racial groups (the opposite of
skin color).
Evolution of Lactose Tolerance
Ancient cultures shifted to a pastural lifestyle.
E. Africa
E. Africa
W. Africa
China
Thailand
Finland
Sweden
% of Population
Lactose Digesters in Human Populations
100
Herders
80
60
40
Farmers
20
0
Soft selection
Fail to
reproduce
Reproduce
successfully
Hard selection
Fail to
reproduce
Reproduce
successfully
Phenotypic value
Relative cutoff
Absolute cutoff
Time
Phenotypic value
Cultural Evolution
Cultural evolution is the change of a society and its
values over time.
Humans have natural social tendencies, but social
behaviors can also be transmitted through nongenetic mechanisms.
In humans, many phenotypes are maintained
through learning in a social environment.
“Homo sapiens is an ordinary species of
animal except that a very large portion of
the individual’s program is carried by the
environment, an environment
rich in conspecifics.”
Dan Janzen
University of Pennsylvania
Humans have an innate ability to add.
Humans have an innate ability to subtract.
Our innate ability is pretty limited.
Learned Concepts of Mathematics
•
•
•
•
•
•
Zero
Infinity
Irrational numbers (e.g., Pi)
Imaginary numbers
Logarithms
Calculus
Other social species also transfer behavior through learning.
Do humans still evolve?
• Strong evidence exists for recent
evolution in Homo sapiens.
• Evolution by natural selection has
slowed for most traits; genetic drift could
be more important now.
• Cultural evolution shapes human
behavior tremendously.