Download Humans Evolved in Response to a Challenge

Humans Evolved in Response to a Challenge
•  Taxonomy, Phylogeny, and the Problem of
Convergence
•  Phylogenetic Trees Based on Molecular Data
•  The Concept of Molecular Clocks
•  DNA Hybridization as an Overall Method for
Counting Mutations
•  Traditional Versus Molecular Data for Hominoid
Phylogeny
•  Hominins Evolved Rapidly in Response to a
Climate Change
•  Exact Nature of Some Genetic Differences between
Humans and Other Primates
Figure 2.2: Modern primate taxonomy. Figure S3a: Carl von Linné
(1707-1778), aka Carolus Linnaeus, was a
Swedish professor of botany,
naturalist, and poet.
He laid the foundations for the
binomial nomenclature (genus,
species) of organisms. His book
Systema Naturae (10th ed., 1758)
classified 4,400 animal and 7,700
plant species. The Lutheran archbishop of
Uppsala accused him of
“impiety” for placing the human
among the primates.
Figure 3.1:
The concept of
a “natural”
taxonomic tree
Defining Human Characteristics
• 
• 
• 
• 
• 
Habitual bipedalism, thumb fully opposable
Exceptional brain size, ability to learn/solve problems Tool making
Art, complex spoken languages
Reproductive and sexual characteristics
–  Family units within large communities
–  Conspicuous female breasts, independently of nursing
–  Concealed estrus, female receptivity throughout menstrual
cycle
–  Modesty
–  Sexual intercourse in private, long lasting
–  Interpretation: Monogamous family units are stabilized by
sexual bonding, which promotes male confidence in
paternity and willingness to help with raising children.
Hominoidea: Traditional taxonomic system
From
Turnbaugh et
al. (1993)
Figure 2.2: Modern primate taxonomy. Humans Evolved in Response to a Challenge
•  Taxonomy, Phylogeny, and the Problem of
Convergence
•  Phylogenetic Trees Based on Molecular Data
•  The Concept of Molecular Clocks
•  DNA Hybridization as an Overall Method for
Counting Mutations
•  Traditional Versus Molecular Data for Hominoid
Phylogeny
•  Hominins Evolved Rapidly in Response to a
Climate Change
•  Exact Nature of Some Genetic Differences between
Humans and Other Primates
Humans Evolved in Response to a Challenge
•  Taxonomy, Phylogeny, and the Problem of
Convergence
•  Phylogenetic Trees Based on Molecular Data
•  The Concept of Molecular Clocks
•  DNA Hybridization as an Overall Method for
Counting Mutations
•  Traditional Versus Molecular Data for Hominoid
Phylogeny
•  Hominins Evolved Rapidly in Response to a
Climate Change
•  Exact Nature of Some Genetic Differences between
Humans and Other Primates
Humans Evolved in Response to a Challenge
•  Taxonomy, Phylogeny, and the Problem of
Convergence
•  Phylogenetic Trees Based on Molecular Data
•  The Concept of Molecular Clocks
•  DNA Hybridization as an Overall Method for
Counting Mutations
•  Traditional Versus Molecular Data for Hominoid
Phylogeny
•  Hominins Evolved Rapidly in Response to a
Climate Change
•  Exact Nature of Some Genetic Differences between
Humans and Other Primates
Double-stranded DNA
becomes singlestranded (“melts”), if
warmed to near 90 0C.
When allowed to cool
down, the single
strands will hybridize
again, with repetitive
sequences (A, color)
becoming doublestranded first.
From Sci. Amer. Vol.
222/issue 4/page 25
Figure 3.2: The melting of double-stranded DNA by heat can be
monitored by measuring its UV absorption, which increases as the DNA
strands separate. The "melting curve”, i.e. a plot of the percentage of
single-stranded DNA vs. temperature, rises sharply between 85 and 90 oC. Figure 3.3:
Base pair
mismatches
in hybrid
DNA cause
a loss of
hydrogen
bonds and a
resulting
decrease in
melting
temperature.
Figure 3.4: ∆T. The “melting
temperature”
of DNA
decreases by a
small
differential
(∆T ) when
some of the
base pairs are
mismatched,
as in hybrid
DNA from
two species. !
Figure S3.b: Lowered melting points (Delta T50H) of
hybrid DNA from combinations of hominoid species. From Sibley and Ahlquist (1984)
Figure 3.5:
Hominoid taxonomy
based on DNA
hybridization data.
The time calibration is
based on fossil data
indicating that the
orangutan lineage
diverged from African
apes 17 million years ago
(MYA). From Sibley and Ahlquist (1984)
Humans Evolved in Response to a Challenge
•  Taxonomy, Phylogeny, and the Problem of
Convergence
•  Phylogenetic Trees Based on Molecular Data
•  The Concept of Molecular Clocks
•  DNA Hybridization as an Overall Method for
Counting Mutations
•  Traditional Versus Molecular Data for Hominoid
Phylogeny
•  Hominins Evolved Rapidly in Response to a
Climate Change
•  Exact Nature of Some Genetic Differences between
Humans and Other Primates
Figure 3.6: The molecular tree (to the right) reflects the likely course of evolution. In
this tree
- the family Pongidae include only one extant species, Pongo pygmaeus, - humans share another family, the (Hominidae), with all African great apes, - the last common ancestor of humans and non-human primates is more recent. - humans and their fossil ancestors are placed in an infrafamily (Hominini).
Fig. 3.6: The traditional and molecular taxonomic trees of the Hominoidea
can be reconciled by assuming that è humans and all great apes are genetically similar
è an unusually large fraction of the DNA mutations of the Hominini (yellow
line) had major phenotypic effects that were positively selected for. Fig. 3.6: To reconcile the traditional and molecular taxonomic trees of the
Hominoidea, è there must be mutations that have major phenotypic effects.
Are there such mutations?
Figure S3.c: Loss of embryonic function in
the Ultrabithorax gene of the fruit fly
Drosophila melanogaster
Top left and right: wild-type. Note club-shaped
balancer organs (halteres) on third thoracic segment.
Bottom: Loss of Ultrabithorax gene activity causes
the replacement of the third thoracic segment (incl.
halteres) with a duplication of the second thoracic
segment (incl. wings).
(a)
(b)
Fig. S3.d: Abnormal self-assembly
of hemoglobin molecules in
humans with sickle cell anemia.
(d)
(c)
a) SEM of normal red blood cell
(b) SEM of sickled red blood cell
(c) Electron micrograph of fiber formed by
hemoglobin S (tetramer carrying two β
globins with the 6 val → glu substitution)
(d) Model of self-assembled hemoglobin
S. Each circle represents a hemoglobin S
tetramer. Fig. 3.6: To reconcile the traditional and molecular taxonomic trees of the
Hominoidea, è there must have been circumstances that left the common ancestors of the
Panini and the Hominini in a state of poor adaptation.
Humans Evolved in Response to a Challenge
•  Taxonomy, Phylogeny, and the Problem of
Convergence
•  Phylogenetic Trees Based on Molecular Data
•  The Concept of Molecular Clocks
•  DNA Hybridization as an Overall Method for
Counting Mutations
•  Traditional Versus Molecular Data for Hominoid
Phylogeny
•  Hominins Evolved Rapidly in Response to a
Climate Change
•  Exact Nature of Some Genetic Differences between
Humans and Other Primates
Figure 3.7:
Sahelanthropus
chadensis
Dated 6-7 million
years ago, and
found in the
Djurab desert of
Chad/Central
Africa, this skull
is the oldest bona
fide hominin
fossil so far. Figure 3.8: About 10-5 mya, a climate change in Africa replaced
much tropical forest with open habitats. The resulting change in
natural selection facilitated the rapid evolution of hominins (From
Lewin, 1993a). Humans Evolved in Response to a Challenge
•  Taxonomy, Phylogeny, and the Problem of
Convergence
•  Phylogenetic Trees Based on Molecular Data
•  The Concept of Molecular Clocks
•  DNA Hybridization as an Overall Method for
Counting Mutations
•  Traditional Versus Molecular Data for Hominoid
Phylogeny
•  Hominins Evolved Rapidly in Response to a
Climate Change
•  Exact Nature of Some Genetic Differences between
Humans and Other Primates
Mutations that are Well
Conserved in Hominin Lineage
•  In coding regions
–  ASPM+ : encodes microtubule-associated
protein. Loss of function inhibits brain growth.
–  FOXP2+ : encodes transcription factor. Loss of
function causes speech impairment.
•  In gene expression
–  Lac+ gene expressed beyond weaning in human
populations herding mammals.
Figure 3.9: Genes and phenotypic traits."
Gene a, affecting more than one trait, is pleiotropic. Trait 2,
being affected by more than one gene, is polygenic.
Humans Evolved in Response to a Challenge
•  Taxonomy, Phylogeny, and the Problem of
Convergence
•  Phylogenetic Trees Based on Molecular Data
•  The Concept of Molecular Clocks
•  DNA Hybridization as an Overall Method for
Counting Mutations
•  Traditional Versus Molecular Data for Hominoid
Phylogeny
•  Hominins Evolved Rapidly in Response to a
Climate Change
•  Exact Nature of Some Genetic Differences between
Humans and Other Primates
80 0C
95 0C
80 0C
Tracer & Driver.
If radiolabeled single-sequence
(ss) DNA (“tracer DNA”, red)
from species X is mixed with
excess unlabeled ss DNA
(“driver DNA”, blue) from
species Y, then any given
labeled strand is more likely to
hybridize with a
complementary unlabeled
strand than with a
complementary labeled strand.
Most of the radioactivity will
then be present (and measured)
in hybrid DNA. From Sci. Amer. Vol. 222/
Issue 4