DESCENT WITH MODIFICATION: A

DARWINIAN VIEW OF LIFE

CHAPTER 22

“ Nothing in Biology makes sense except in the light of evolution”T.B. Dobzhansky

Figure 22.2 Fossils of trilobites, animals that lived in the seas hundreds of millions of years ago

HISTORICAL CONTEXT

Carl Linnaeus (1707-1778) – founder of taxonomy (scientific name) grouped similar species into same genus

Georges Cuvier (1769-1832) – catastrophism – different species in layered rock due to catastrophic events like floods

James Hutton (1726-1797) – gradualism – profound change is a cumulative product of slow but continuous process; ex. Rivers making canyons

Charles Lyell (1797-1875) – uniformitarianism – geological process have not changed throughout Earth’s history

Jean Baptiste Lamarck (1744-1829)- thought acquired characteristics can be passes on to offspring

Figure 22.3 Formation of sedimentary rock and deposition of fossils from different time periods

Figure 22.4 Strata of sedimentary rock at the Grand Canyon

Figure 22.18 Charles Darwin in 1859, the year The Origin of Species was published

CHARLES DARWIN (1809-1882)

Worked on the HMS Beagle in 1830’s

Observed and collected thousands of different species

Galapagos Islands (west of S. America) most interesting

Figure 22.5 The Voyage of HMS Beagle

Figure 22.6 Galápagos finches

“The Galápagos tortoise (or Galápagos giant tortoise), is the largest living tortoise, endemic to nine islands of the Galápagos archipelago. Adults of large subspecies can weigh over 300 kilograms (660lb) and measure 1.2 meters (4 ft) long. Although the maximum life expectancy of a wild tortoise is unknown, the average life expectancy is estimated to be 150-200 years.”Source: en.wikipedia.org/wiki/Gal%C3%A1pagos_tortoise

Darwin read Lyell’s Principles of Geology and felt age of earth was much older than previously thought

1844 Darwin wrote essay on the origin of species

1858 – Alfred Wallace sends manuscript to Darwin about Natural Selection

Lyell presented Wallace’s paper as well as Darwin’s 1844 essay to scientists

1859 The Origin of Species published by DarwinDescent with modificationNatural selection (the

mechanism)

Figure 22.7 Descent with modification

DARWIN’S OBSERVATIONSPopulation size can lead to

struggle for existenceIndividuals who inherited

characteristics best fit for environment are likely to have more offspring than less fit individuals

Leads to gradual change in a population

NATURAL SELECTION

A population evolves, not an individual!

Acquired characteristics may be adaptable but are not inherited!!

The environment does not create a best fit characteristic, but selects for it!

Figure 22.9 A few of the color variations in a population of Asian lady beetles

Figure 22.11b Artificial selection: diverse vegetables derived from wild mustard

AP:April. 29, 2005 ST. THOMAS, Barbados - It's male.  But what is it?  A zonkey? A deebra?  That's the debate in Barbados since a zebra gave birth to a foal sired by a donkey.

Goldendoodle and a liger

EVIDENCE OF EVOLUTIONBiogeography – geographical

distribution of speciesEx. Islands with similar species

to mainlandFossil record – transitional

formsComparative Anatomy –

homologous structures among different organisms

Vestigial organs –marginal, if any importance, remnants of structures that once served a functionWhale pelvis and leg bones and

human appendixComparative Embryology – most

vertebrates share common early development (gill slits)

Molecular Biology – similar overall DNA, similar proteins (ex. Cytochrome c)

Figure 22.12 Evolution of insecticide resistance in insect populations

Figure 22.13 Evolution of drug resistance in HIV

Figure 22.14 Homologous structures: anatomical signs of descent with modification

Table 22.1 Molecular Data and the Evolutionary Relationships of Vertebrates

Figure 22.15 Different geographic regions, different mammalian “brands”

Figure 22.16 The evolution of fruit fly (Drosophila) species on the Hawaiian archipelago

Figure 22.17 A transitional fossil linking past and present