CHAPTER 16: DARWIN’S THEORY OF EVOLUTIONSection 16-4: Evidence of Evolution

BIOGEOGRAPHY

The study of where organisms live now and where they and their ancestors lived in the past

Patterns of distribution tell how modern organisms evolved from ancestors

Two patterns important to Darwin: Closely related but different – Galapagos

species similar to mainland species, suggests natural selection caused variations

Distantly related but similar – similar habitats can lead to similar adaptations in distantly related species

THE AGE OF THE EARTH AND FOSSILS

Hutton/Lyell argued Earth was old – but how old?

Modern geologists use radioactive dating to determine age of rocks/fossils

Earth is about 4.5 billion years old Darwin’s study of fossils convinced him, but

paleontologists had not yet found enough fossils of intermediate species

Since then, many have been found Whales from ancient land mammals

RECENT FOSSIL FINDS

History of life incomplete Always more to learn Evidence shows change

COMPARING ANATOMY AND EMBRYOLOGY All vertebrate limbs have same basic bone

structure Animals with similar structures evolved from

common ancestor Homologous structures – same basic

structure, shows common ancestry – different function

Study anatomical details, development in embryos, pattern of appearance

Similarities/differences show how recently organisms shared a common ancestor

COMPARING ANATOMY AND EMBRYOLOGY

Common structure = common descent, not common function

Body parts that share common function but not structure are analogous structures

Bee wing and bird wing

COMPARING ANATOMY AND EMBRYOLOGY

Vestigial structures – inherited from ancestors but have lost much of their original function

Ex: hipbones of dolphins, wings of flightless birds

Maybe presence of structure has no affect on fitness

COMPARING ANATOMY AND EMBRYOLOGY

Early developmental stages of many vertebrates look similar

Cells develop in the same order Shows common ancestry

GENETICS AND MOLECULAR BIOLOGY

Central dogma Genetic code is universal – most organisms

share the same genes Shows common ancestry

HOMOLOGOUS MOLECULES

Homologous proteins share structural/chemical similarities

Ex: Similar versions of cytochrome c (cellular respiration) found in all living cells

Can also have homologous genes – Hox genes direct limb development

Minor changes in genes leads to major changes in structures

TESTING NATURAL SELECTION

Gather evidence by observing it in action

Grants and the Galapagos finches (read in text!) Showed competition and environmental change

drive natural selection Heritable variation the key – increased variation

increases likelihood of adapting/surviving changes

EVALUATING EVOLUTIONARY THEORY

Theory of evolution considered the grand unifying theory of the life sciences

Constantly being reviewed as new data is gathered

Questions that remain are about how evolution works, not whether it occurs