Chapter 22: Evolution

Evolution

Heritable change in one or more characteristics of population or species from one generation to next

Microevolution

Changes in single gene in population over time

Macroevolution

Formation of new species or groups of species

Species

Group of related organisms that share distinctive form

History of theory of evolution

Mid to late 1600's
*John Ray studies natural world
*George Buffon forms change over time
*Jean-Baptiste Lamarck some animals remain same while others changed
*Living this evolved upward toward human "perfection"
*inheritance of acquired characteristics (Giraffe necks)

Geology & population growth

Uniform action hypothesis
*slow geological processes lead to substantial change
*earth much older than 6000 years
*Thomas Malthus only fraction of any population will survive & reproduce

Charles Darwin

Ideas influenced by own observations
*studied Galapagos Island Finches
*formulated theory of evolution by mid 1840's
*On the Origin of Species published 1859 (ideas + observational support)

Descent with modification

Variation with given species
*traits heritable
Natural selection
*more offspring produced that can survive
*competition for limited resources
*individual with better traits

Selective breeding (artificial selection)

Darwin influenced by pigeon selection
*nature chooses parents in natural selection while breeders choose artificial
*possible by genetic variation
*breeders choose desirable phenotypes (visible features)

Biogeography

Study of geographical distribution of extinct & modern species
Endemic: naturally found only in particular location isolated continents & island groups have evolved their own distinct plane & animal communities

Evolution of major animal groups

Correlated with unknown changes in distribution of land masses on earth
-first mammals 200 million years ago years ago when Australia was still connected
-placental mammals 80 million years ago years after Australia separated

Convergent evolution

Two different species from different lineages show similar characteristics because they occupy similar environments

Fishapod (Tiktoak roseae)

Illuminates steps leading to evolution of tetrapods
Transitional form provides link between earlier & latere forms
-peak above water & search for prey

Whales from terrestrial mammals

Fossils span 50 million years years
Lack hind limbs
Whales, dolphins, porpoises (Hippo to whale)

Homology

Fundamental similarity due to descent from common ancestor (anatomical, developmental, molecular)

Anatomical homology

Same set of bones/limbs of modern vertebrates undergone evolutionary change
Homologous: derived from common ancestor
Vestigial: no apparent function but resemble structures of presumed ancestors

Developmental homology

Species that differ as adults often bear striking similarities during embryonic stages
-gill ridges in human embryos indicate that humans evolved from acoustic animal with gil slits

Molecular homology

Same type of gene often found in diverse organisms,such as
Ex. p53 gene encodes p53 protein
-sequences of closely related species tend to be more similar to each other than to distantly related species