CHAPTER 22 DESCENT WITH MODIFICATION

By Charith Samarasena

Vocabulary

Fossils: the remains or traces of organisms from the past

Strata: layers of sediment Paleontology: the study of fossils Catastrophism: the principle that events in the past

occurred suddenly and were caused by mechanisms different from the present

Gradualism: mechanisms of change occur gradually over time

Uniformitarianism: mechanisms of change are constant over time

Adaptations: characteristics of an organism that enhance their survival and reproduction in specific environments

Vocab cont’d

Natural Selection: the process in which individuals with certain inheritable traits leave more offspring than individuals with other traits

Artificial Selection: the selective breeding of domesticated plants and animals to encourage the occurrence of desirable traits

Homology: similarity of characteristics resulting from a shared ancestry

Vestigial Structures: historical remnants of structures that had important functions in ancestors but no use in current organisms

Evolutionary Tree: a branching diagram that reflects a hypothesis about evolutionary relationships among groups of organisms

Vocab still cont’d

Convergent Evolution: the evolution of similar features in independent lineages

Analogous: having characteristics that are similar because of convergent evolution, not homology

Biogeography: the study of past and present distribution of species

Plate Tectonics: theory of how landmasses move along the earth’s crust

Endemic: where a species of plant or animal is only found in one particular location

Theory: a hypothesis that is supported by evidence and has been tested repeatedly with success

What is Evolution and why is important?

Evolution is the process in which species have modifications of certain traits that allow them to adapt to changes in environments

It’s important because it helps explain how some species in one location don’t look like other species in another location

It’s also explains why current organisms don’t resemble their ancestors

Carolus Linnaeus

He developed a two-part system of naming organisms according to genus and species

Georges Cuvier

Largely developed the field of paleontology

Observed that older layers of strata contain fossils of organisms that are more and more dissimilar to today’s organisms

Also came up with the principle of catastrophism

James Hutton

Proposed that Earth’s geological features could be explained by gradual mechanisms in the past that still occur today (ex. Continental drift)

Charles Lyell

Came up with the principle of uniformitarianism and also thought that this process still occurred today

Jean-Baptiste de Lamarck

Observed that older to younger fossils lead to living species

Hypothesized that structures that are used more frequently than others grow larger and stronger, and the structures that aren’t used deteriorate over time

Also hypothesized that organisms could pass on these modifications to offspring

Also thought that evolution occurs because organisms have an innate drive to become more and more complex

Charles Darwin

Proposed the idea of descent with modification by natural selection

Observed this in various finches while exploring the Galapagos Islands

What did Charles Darwin conclude after his voyage on the H.M.S. Beagle?

The Five Points of Evolution: 1. Organisms produce more offspring than necessary. 2. There is a variation in the offspring’s traits. 3. Competition among offspring cause many to die

out (as do the lack of food and resources). 4. Natural Selection favors the traits of the offspring

that survive. 5. Evolutionary changes in organisms occur over

time.

NOW WHAT EVIDENCE IS THERE THAT SUPPORTS THESE POINTS?

The Fossil Record

Fossils of past organisms show that there have been evolutionary changes over time to shape organisms into the forms of today

Homology

Homologous and Vestigial structures show similarities of structures in different species

DNA & RNA

The genetic code is essentially universal in all organisms; this shows evidence of common ancestry

Biogeography

Distribution of organisms allows paleontologists to figure out where fossils will be

Also shows similarities of species in different areas