BIOL&212 Animals (Metazoans) -...
Transcript of BIOL&212 Animals (Metazoans) -...
Early attempts at organization and naming
• Carolus Linneaus:Systema Naturae (1735).
Two advances • Hierarchical classification
based on “ideal of unchanging types”. – K, P,C, O, F, G, S
• Binomial nomenclature - replaced polynomials
• Assumes a static, unchanging Universe
Charles Darwin • 1809-1882 • Englishman; bound for
medicine…then the clergy…sidetracked by biology
• 1831-1836 Beagle; visits isolated archipelago – 1839 Journals
• 1859 The Origin of Species! – Outlined the process of evolution
via natural selection • Demonstrated that life is
dynamic
Observations that suggested change over time
• Fossil Record – Layering of simple to complex – Extinctions – Succession & Transitional forms
• Environmental/Geological change • Vestigial traits • Apparent relatedness of species correlates with geographic distribution
Fossil record • Fossils of complex organisms occur closer to the
surface, in rocks of younger age, than those of simpler organisms. This layering was globally consistent suggesting they were different ages. – Darwin had huge collections to examine, even in early
1800’s
Extinctions • Some fossils clearly belonged to creatures no
longer walking the Earth – Irish elk – More famous examples like T. rex
Transitional Forms & Environmental Change
• “fossil sandwiches” occurred in these rock layers; middle fossils intermediate in form between fossils above and below.
• Documented changes in skeletal morphology through time
Succession of forms • Darwin’s
predecessors – Morphology of fossil
species often closely match the morphology of contemporaries
– Law of Succession
Apparent Relatedness • Darwin’s contribution came after and
almost certainly as a result of his voyage through the Galapagos island archipelago
• 1831 - Charles Darwin (22) joins crew of HMS Beagle as gentleman’s companion (ship’s naturalist) & collects & catalogues everything. (1831-36) – Plants, insects, fossils & Galapagos “finches” – After his return he and his naturalist friends
noted some things about his collections:
Weight of evidence lead to his heretical proposal:
• H: Species on neighboring islands look similar because they are all descended from a common ancestor; The small differences between them are due to changes over time. – A bold assertion & dangerous for the time. Species are not static!!
• So, he waited ~20 years after developing the idea to publish it
OK, so what’s the mechanism for change?
Differential survival & Reproduction
Variation is heritable
Beneficial variants leave more offspring
Variable traits
On the Origin of Species by Means of Natural Selection, or the Preservation of Favored Races in the Struggle for Life
-Charles Darwin, 1859 • Darwin’s “blackbirds”, “gross-
beaks”, “wrens” and finches
Darwin’s postulates (hypotheses)
1. Traits in a population vary among individuals 2. Some traits are passed on to offspring (i.e.
traits have a genetic basis and are heritable) 3. Due to environmental challenges (ex: struggle
for resources), some individuals produce more offspring than others
4. The subset of all offspring that survive are those that possess beneficial traits; these traits (and the individual carrying them) are “naturally selected” by the environment.
What was Darwin’s contribution?
• Others had proposed evolution (of some variety) as a pattern that required explanation.
• Darwin provided the process, natural selection, that explained the pattern of descent with modification.
Darwin introduced “fitness” to explain natural selection
• Fitness: the ability of an individual to produce fertile offspring, relative to that ability in other individuals. – This is a measurable quantity, and allows us to
define adaptation • Adaptation: a heritable trait that
increases the fitness of an individual relative to individuals lacking that trait. – These are time and location (environmentally)
dependent
Contemporary evidence in support of evolution
• Homologous traits – Structural/Morphological: Outward physical
appearance – Developmental: Sequence & timing of developmental
events; shared germinal tissues – Genetic: DNA sequence
• Direct observation: MRSA, soapbug beak length
• Convergent traits: Distant relatives have nearly identical traits
Structural • Limbs with radically different functions are all
built from bones of similar shape, in same orientation & same relative positions. – Why, unless this structural archetype was present in
the common ancestor of all?
Developmental • Chick, human and cat embryos have gills and tails; they
appear at similar developmental stages & in the same positions as those of fish. Why?
• Fish & human jaws look very different, but develop from same population of embryonic cells. Why should they?
Genetic • The same 64 codons specify the same building
blocks in ALL organisms. Why? • Many genes are found in organisms that are very
different and their sequences are nearly identical. – Ubiquitin is found in ALL Eukaryotes; its DNA sequence
is 96% identical between humans and yeast. Why?
Direct Observation
• Soapbugs – Host plant switch – Choice of host
correlates with beak length
– Reduced gene flow – Diversification
follows
Convergent traits • distantly related
species that share common environmental challenges have similar traits
Base groupings upon shared (homologous) traits
• Animals that share the most traits are most closely related.
• What is a trait? – Morphologic – physical appearance – Developmental sequence – physical
appearance during embryonic development; common cell fates, timing of cell migrations & gene activity
– Genetic – DNA sequence identity; chromosome number