Misconception: Evolution is just a theory.!

Transcription

1 Developing a Theory to Explain Change Section 4.2, pages Misconception: Evolution is just a theory.! The THEORY of evolution! Formalized by Charles Darwin, is as much theory as is the theory of gravity, or the theory of relativity.! Unlike theories of physics, biological theories (especially evolution) have been argued long and hard in socio-political arenas. 1

2 Developing the Theory of Evolution Many scientists and great thinkers have contributed to our understanding of life on Earth, especially evolution. Plato and Aristotle (300 B.C.) Natural Theology was a philosophy dedicated to discovering the creators plan by studying nature. believed that all life existed in a perfected and unchanging form dominated western thought for centuries The Great Chain of Being Scala Naturae a major objective of natural theology was to classify species in order to reveal the steps of the scale of life that God had created. God angels mankind each living form fits its environment perfectly all creatures created independently of one another by God Since God is perfect, his creation must be perfect (and unchanging) No gaps in the chain: no extinction, no new forms animals plants minerals Dirt 2

3 Carolus Linnaeus (1735) Father of Modern Taxonomy Systema Naturae - Taxonomy is the branch of biology concerned with naming and classifying the diverse forms of life. - Linnaeus developed a binomial system of naming organisms according to genus and species that is still in use today. - He also adopted a system for grouping similar species into a hierarchy of increasingly general categories. Linnaeus wanted to catalog God s creation to be able to come closer to God. At this time, there was little distinction between philosophy and science Classification system like a branching family tree of life. 18 th Century The Age of Enlightenment Georges-Louis Leclerc, Comte de Buffon (mid 1700 s) Proposed that species could change. Provided evidence of descent with modification and speculated on various causative mechanisms: influences of the environment, migration, geographical isolation, overcrowding, and the struggle for existence. 3

4 Georges Cuvier (late 1700 s) founded vertebrate paleontology recognized that the history of life was recorded in strata containing fossils. He noted that the deeper you go into the strata, the more different the life forms were from moderns life firmly established the fact of the extinction of past lifeforms. "Why has not anyone seen that fossils alone gave birth to a theory about the formation of the earth, that without them, no one would have ever dreamed that there were successive epochs in the formation of the globe." Georges Cuvier Discourse on the Revolutions of the Surface of the Globe 4

5 A gallery of fossils Cuvier advocated the idea of Catastrophism, speculating that each boundary between strata corresponded in time to a catastrophe, such as a flood or drought. He also said that after catastrophes, areas struck were repopulated by species immigrating from other areas. James Hutton (1795) Gradualism - features and changes in the land are the cumulative product of slow but continuous geological processes. 5

6 Charles Lyell (1830) published Principles of Geology uniformitarianism - continuous geological processes are still occurring the same way today as they did in the past. Formation of sedimentary rock and deposition of fossils from different time periods The Big Picture: 1) The earth is very old (much older than 6000 yrs accepted at the time via biblical reference). 2) slow and subtle processes over long periods of time can cause huge changes evolution. A lot can happen in a few million years. Ersamus Darwin (Charles Darwin s grandfather) ( ) One of the leading intellectuals of 18th century England, a man with a remarkable array of interests and pursuits. He was a respected physician, a well known poet, philosopher, botanist, and naturalist. As a naturalist, he formulated one of the first formal theories on evolution in Zoonomia, or, The Laws of Organic Life ( ). 6

7 Jean-Baptiste Lamarck (early 1800 s) developed one of the first theories on how species changed Lamarck, in 1809, concluded that organisms of higher complexity had evolved from preexisting, less complex organisms. He proposed the inheritance of acquired characteristics to explain, among other things, the length of the giraffe neck. Mechanism of evolution: Use and disuse (driven by need ) Lamarck's scientific theories were largely ignored or attacked during his lifetime. Today, the name of Lamarck is associated merely with a discredited theory of heredity, the "inheritance of acquired traits." However, Charles Darwin, acknowledged him as a great zoologist and as a forerunner of evolution. Charles Darwin wrote in 1861: Lamarck was the first man whose conclusions on the subject excited much attention. This justly celebrated naturalist first published his views in he first did the eminent service of arousing attention to the probability of all changes in the organic, as well as in the inorganic world, being the result of law, and not of miraculous interposition. 7

8 Evolution of the long-necked giraffe Requirements: - Variation in a trait within a opulation. (Giraffe's necks) - More individuals are born each generation than can survive: the "Struggle for Existence" 8

9 - Giraffes with longer necks get better food, have more babies (have an advantage in the struggle for existence) "Longer necks beget longer necks (variation is heritable) Results: Over time, average neck length increases!many researchers now suggest that the primary function of giraffe neck length is not for reaching leaves on tall trees, but for male combat ( necking ), or for spotting predators, or for shedding heat through increased skin surface area. All of these functions have been viewed by prominent scientists as a chief reason for the evolution of the long necks Darwin himself alludes to some of these as alternate possibilities. 9

10 Brief Biography: Charles Darwin was born in 1809 (dies 1882) Went to school in Edinburgh to study medicine like his father Switched to the study of clergy at Cambridge Enjoyed being in the woods, studying plants and animals After school, Darwin signed on as ship s naturalist on the HMS Beagle From The HMS Beagle traveled through South America, mapping and collecting 10

11 Galapagos Islands The Galapagos Islands (off the coast of Ecuador) 11

12 Galapagos finches An example of adaptive radiation Darwin didn t come up with his theory of natural selection until after his return to England 3 major Influences on Darwin: - Voyage on the Beagle - Thomas Malthus, Essay on the Principle of Population (1798) - Charles Lyell, Principles of Geology (1830) Thomas Malthus ( ) Darwin starts to outline his theory: In 1844, Darwin wrote an essay outlining his ideas, to be published on the event of his death Continued to collect data, to be included in his big book 12

13 Alfred Russell Wallace Avid Naturalist: traveled to Malaysia and South America, collecting specimens to sell in order to finance his trips In 1858, while suffering from a bout of Malaria, came up with the theory of natural selection independently of Darwin ( ) Sent a few pages of On the tendency of varieties to depart indefinitely from the original type to Darwin jointly presented their ideas to the Linnaean Society in London Charles Darwin in : Darwin publishes On the Origin of Species by Means of Natural Selection Darwin proposed 2 main ideas: 1. present forms of life have arisen by descent and modification from an ancestral species. 2. The mechanism for modification is natural selection working for long periods of time 13

14 On the Origin of Species by Means of Natural Selection 5 main components 1. Overproduction Number of offspring by a species is greater than can survive and reproduce Salmon eggs! 14

15 2. Struggle for Existence Organisms of the same species (and other species) must compete for the same limited resources 3. Variation Differences among traits occurs by chance; no two individuals are exactly alike. 15

16 Offspring inherit most of parentʼs traits, but not all of them! Some traits arise randomly, by genetic mutation! 4. Survival of the Fittest The environment acts to select favorable traits (not create them). Those with an advantage survive and reproduce, increasing their numbers. This is selection by nature, hence, natural selection (1) Population with varied inherited traits (2) Elimination of individuals with certain traits (3) Reproduction of survivors 16

17 Galápagos finches 5. Speciation Individuals do not change, populations change over time. Accumulation of new, favorable traits over a long period of time population so different new species 17

18 Blue-black Grassquit common ancestor of Galapagos Finches may have been similar to this species, found in Central and South America Galapagos finches An example of adaptive radiation If members of a population become geographically isolated from the main group, they may become so different that they are no longer able to reproduce with members of the original population (new species) 18

19 The Kaibab squirrel became geographically isolated from the common ancestor with its closest relative, the Abert squirrel in the North Rim of the Grand Canyon about 10,000 years ago. Since then, several distinguishing features, such as the black belly and forelimbs have gradually evolved. Kaibabs squirrel! Alberts squirrel! How can we explain the origin of the tremendous biodiversity seen on Earth? Modern examples of evolution" John Endler performed experiments in microevolution, allowing artificial selection to manipulate the spots on guppies. Guppy spots are largely genetically controlled. Spots that help the guppy blend in with its surroundings protect it from predation but spots that make it stand out help it attract mates 19

20 Introduce a predator! 15 generations later! After fewer than 15 generations of selection, the markings of guppies in different ponds had substantially diverged as a result of natural selection. In the presence of predators, guppies evolved to blend in with their background. 15 generations later! 20

21 Without predators, there was sexual selection for male guppies that stood out from their background and attracted the attention of the females. Stages in the evolution of the horse (Equus) 21