BIO120H1 Chapter Notes - Chapter 4: Zoology, Molecular Clock, Marsupial

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19 Sep 2018
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BIO120: Why Evolution is True, Jerry A. Coyne (Ch.4 The
Geography of Life)
In association with Reading Quiz 3 and Lecture 3
The Geography of Life
- There are three islands of Juan Fernandez that are living museums of rare and exotic plants and
animals, with many species endemic 5 species of birds, 126 species of plants, handful of
insects; harbors no species of mammals, amphibians, reptiles, or mammals
- The roots of biogeography lie deep in religion where natural theologians tried to show how the
distribution of organisms could be reconciled with the account of Noahs Ark in the bible
- In mid-1800s, Louis Agasiz, a zoologist, asserted that not only were species immutable and
static, but so where their distributions, with each remaining at or near their site of creation
several developments made this idea untenable
- Fossil seashells high in Andes proved that mountains present today were once underwater
- Darwin proposed his theory where the distributions of species were explained not by creation, but
by evolution; if plants and animals dispersed over large distances and could evolve into a new
species after they dispersed, then this, along with some ancient earth shifting (e.g. glacial
expansion) could explain peculiarities of biogeography
- Dispersal of animals can be explained by two recently discovered developments on evolutionary
theory
o Continental drift
o Molecular taxonomy
- Evolutionary theory predicts, and data supports the idea that as species diverge from their
common ancestors, their DNA sequences change in roughly a straight-line fashion with time.
This molecular clock calibrated with fossil ancestors of living species, can be used to estimate
the divergence times of species that have poor fossil records
- Evolutionary relationships between species can be matched using molecular clock and known
movements of the continents and glaciers and formation of genuine land bridges (E.g. isthmus of
Panama)
- Biologists can deduce why species live where they do
o E.g. similarities between African and South American plants can be explained by their
ancestors who once inhabited a supercontinent (Gondwana) that split into several pieces
(Africa, South America, India, Madagascar, and Antarctica)
- Continents
o There are obvious differences between two types of succulents by their flowers and sap
clear and water sap in cacti, milky and bitter in euphorbs; despite differences, they
look very similar
o Creator wouldnt put fundamentally different plants with similar physical features in
ecologically identical places
Can be argued that cacti and euphorbs only work well in their respective habitats,
but when North American prickly pear cactus was introduced into Australia it
became invasive until finally controlled in 1926 by introducing a moth whose
caterpillars devour the cacti
Prickly pear cacti can flourish in their native environments and non-native
environments
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