Post on 21-Dec-2015
Evolution
The definition of Evolution is:
change over time
Biological Evolution is:
genetic change in population over time
process by which modern organisms have descended from ancient organisms (slow change over long time)• Even relatively quick evolution takes hundreds of thousands of years
History of Evolutionary TheoriesPlato (427-347 B.C.) 2 worlds – 1 perfect, 1 imperfect. No change in organisms
Aristotle (384-322 B.C.) Organisms placed on “ladder of complexity / perfection” (scala naturae) No change
Judeo-Christian culture tried to explain the Creator’s plan as observable, natural phenomena – Natural Theology
History of Evolutionary TheoriesCarolus Linnaeus (1707-1832) Designed modern taxonomic system (binomial nomenclature)
From this system, we can (he didn’t) now infer evolutionary relationships between different groups
Geologists:Georges Cuvier
James Hutton
Charles Lyell
History of Evolutionary TheoriesGeorges Cuvier (1769-1832) helped develop Paleontology – study of fossils
Discovery of fossils (extinct species, similarities to modern species) put some doubt into Earth’s age and the origin of species
Cuvier explained differences in strata with “catastrophism” – floods, droughts, volcanoes, etc. changed local areas drastically over short periods of time
• Organisms did not change, just migrate
History of Evolutionary TheoriesJames Hutton (1726-1797) proposed that rocks, mountains, and valleys have been changed by water, wind, temperature, volcanoes, and other natural forces
He described the slow processes that shape Earth as “gradualism”
History of Evolutionary TheoriesCharles Lyell (1797-1875) – agreed with Hutton and said that scientists must always explain past events in terms of observable, PRESENT events and processes (“uniformitarianism” – what happens today happened yesterday)
They theorized Earth was much older than a few thousand (6,000) years, which didn’t set well in the traditional timeframe of Creationism
Age of the EarthWe now know Earth is approximately 4.5 billion years old
Darwin used the work of Hutton and Lyell as a basis for his theories of slow change over time. Darwin’s work was a biological duplicate of Hutton and Lyell’s works in geology.
Geologists study Earth’s rocksFossils are preserved remains of ancient organisms
As fossils are found that don’t resemble organisms today, evidence increases that Earth has changed and that organisms have changed with it
Biologists and geologists date Earth’s past with the help of rocks
Geological Time ScaleRELATIVE DATING
Technique used to determine age of fossils relative to other fossils in different strata
This technique is VERY approximate
Geological Time Scale
ABSOLUTE (RADIOMETRIC) DATING
Using radioactive elements in rock that decay at a steady rate to determine age
Decay measured in terms of HALF-LIFE
• Half-life – time required for half the radioactive atoms in a sample to decay
Radioactive Decay
During radioactive decay, the atoms of one element break down to form something else
6 protons
4 neutrons5 protons
4 neutrons
Lose a proton
Rocks contain radioactive elements, each having a different half-life
EXAMPLES:
Uranium-238 Lead-206 HL = 4.5 B yrs
Potassium-40 Argon-40 HL = 1.3 B yrs
Carbon-14 Nitrogen-14HL = 5770 yrs
Scientists often date rocks using Potassium-40, which decays to form the stable element Argon-40
It has a half life of 1.3 billion years
This is used to date the oldest rocks on earth
K-40
Formed 1.3 B yrs
K-40 Ar-40 Ar-40
2.6 B yrs
Uranium and Potassium are useful for dating rocks
Carbon-14 is useful for dating things that were once alive such as wood, natural fiber, or cloth
C-14 is in the atmosphere; living things take it in their cells. After the organism dies, it doesn’t take in any more C-14. We can then compare the amounts of C-14 to N-14, knowing its half-life, to determine the age of the sample
Fossil Evidence
Found in Sedimentary rock: layers of sand, silt, and clay in streams, lakes, rivers, and seas form rock that may have trapped living organisms
Fossil records – Show change over time. Some time frames are missing, but will show change of climate and geography.
Ex: Shark teeth in Utah
How can this be?
Jean Baptiste de Lamarck (1744-1829)
He also recognized that organisms were adapted to their environments and that they change
He relied on three ideas:
1. A desire to change (innate drive for perfection)
2. Use and disuse (Giraffe’s necks and vestigial organs)
3. Inheritance of acquired characteristics
Darwin’s Dilemma
Set sail around the world in 1831 on HMS Beagle on a 5 year voyage
He had prior knowledge of geology (Lyell was a good friend) and agriculture that helped influence the development of his theory
Anchored all along the way and took samples from each place
Darwin’s Dilemma
He collected and studied beetles from Brazil, birds from Chile, and iguanas, tortoises, and finches from the Galápagos Islands
He noticed similarities between mainland (Ecuador) and Galapagos finches
Later, he noticed differences in beak size among finches from different islands in the Galapagos
Darwin’s Dilemma
Thomas Malthus – wrote paper on population growth in Great Britain
Population grows exponentially
Limiting factors on growth (carrying capacity)
• Food
• Area
• Resources
Darwin’s DilemmaDarwin applied Malthus’, Hutton’s, and Lyell’s work to species’ ability to change, and called the mechanism Natural Selection
Nat.Sel.: Process by which organisms with favorable variations survive and produce more offspring than less well-adapted organisms
He was sure Nat.Sel. was true, but he feared public ridicule. So, he kept his ideas to himself
Darwin’s DilemmaAlfred Russel Wallace (1823-1913), working independently, came to the same conclusions as Darwin
He sent a manuscript to Darwin, basically for proofreading
“I never saw a more striking coincidence… so all my originality, whatever it may amount to, will be smashed.” – Charles Darwin
Letter to Charles Lyell, June 18, 1858
Darwin quickly abridged and published his work “On the Origin of Species”
Darwin’s Natural SelectionErnst Mayr, an evolutionary biologist, has dissected the logic of Darwin’s theory into three inferences based on five observations (Pg. 435)
Observations:
Tremendous fecundity
Stable populations sizes
Limited environmental resources
Variation among individuals
Heritability of some of this variation.
Darwin’s Natural SelectionObservation #1: All species have such great potential fertility that their population size would increase exponentially if all individuals that are born reproduced successfully.
Darwin’s Natural SelectionObservation #2: Populations tend to remain stable in size,except for seasonal fluctuations.
Observation #3: Environmental resources are limited.
Darwin’s Natural SelectionInference #1: Production of more individuals than the environment can support leads to a struggle for existence among the individuals of a population, with only a fraction of the offspring surviving each generation.
Darwin’s Natural SelectionObservation #4: Individuals of a population vary extensively in their characteristics; no two individuals are exactly alike.
Observation #5: Much of this variation is heritable.
Darwin’s Natural Selection
Inference #2: Survival in the struggle for existence is not random, but depends in part on the hereditary constitution of the individuals.
Those individuals whose inherited characteristics best fit them to their environment are likely to leave more offspring than less fit individuals.
Darwin’s Natural Selection
Inference #3: This unequal ability of individuals to survive and reproduce will lead to a gradual change in a population, with favorable characteristics accumulating over the generations.
Evidence in Living Organisms
Comparative embryology:
All vertebrate embryos look similar to one another in early development, with the development of a tail and gill arches
• Ernst Haeckel made early drawings – later exposed as frauds.
• Gave fuel to anti-evolutionists
Evidence in Living Organisms
Comparative embryology:
These anatomical similarities indicate similar genetics are at work
Become more dissimilar as they grow
• Cell specialization and differentiation
Common ancestor?
Evidence in Living Organisms
Comparative anatomy:
Homologous Structures
Analogous Structures
Vestigial Organs
Evidence in Living Organisms
Homologous Structures – structures that are similar in anatomy, but may serve very different functions
Ex: cat, whale, and human forearm
Evidence in Living Organisms
Analogous Structures – structures that serve similar functions, but have evolved independently of each other
NotNot homologous; homologous;notnot analogous analogous Homologous;Homologous;
notnot analogous analogous
NotNot homologous; homologous;analogousanalogous
Homologous; Homologous; analogousanalogous
Evidence in Living Organisms.
Vestigial organs – organs that have little or no purpose in the organism; may become smaller or even disappear
Ex: Tailbone or appendix in humans
Ex: Tiny leg bones in snakes (boas and pythons) thought to come from 4 legged ancestor
Evidence in Living Organisms
Comparative biochemistry and molecular biology:
All cells have DNA, RNA, ribosomes, the same 20 amino acids and use ATP to do work
Similarities in biochemistry indicate relationship
Evidence in Living Organisms
Cytochrome c is a highly conserved respiratory protein containing 104 amino acids in humans