Humans Evolved in Response to a Challenge

Transcription

1 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

2 Figure 2.2: Modern primate taxonomy.

3 Figure S3a: Carl von Linné ( ), 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.

4 Figure 3.1: The concept of a natural taxonomic tree

5 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.

6 Hominoidea: Traditional taxonomic system From Turnbaugh et al. (1993)

7 Figure 2.2: Modern primate taxonomy.

8 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

9 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

10 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

11 Double-stranded DNA becomes singlestranded ( melts ), if warmed to near 90 0 C. 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

12 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 o C.

13 Figure 3.3: Base pair mismatches in hybrid DNA cause a loss of hydrogen bonds and a resulting decrease in melting temperature.

14 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.!

15 Figure S3.b: Lowered melting points (Delta T 50 H) of hybrid DNA from combinations of hominoid species. From Sibley and Ahlquist (1984)

16 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)

17 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

18 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).

19 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.

20 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?

21 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).

22 (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.

23 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.

24 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

25 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.

26 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).

27 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

28 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.

29 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.

30 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

31 80 0 C 95 0 C 80 0 C 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