Evidence for Darwin’s Theory of Evolution

Why Do Scientists Accept It?

The Evidence Falls Into Several Categories Structural Adaptations Physiological Adaptations Fossils Anatomy Embryology Biochemistry

Adaptations

An adaptation is any variation that aids an organism’s chances of survival in its environment.

Structural adaptations: mole-rats have adaptations to live underground that have evolved over millions of years (large teeth, large claws). Other examples? Thorns of plants and porcupine’s quills.

Mimicry and Camouflage

Mimicry: One species evolves to look like another. Harmless scarlet king snake looks like poisonous coral snake. Predators avoid both.Or, several harmful species evolve to resemble each other – bees, wasps, yellow jackets.

Camouflage: Organism blends into its background. Predators don’t notice it. Can you give examples?

Physiological Adaptations

Many bacteria have evolved to be resistant to penicillin which was a “wonder” drug 50

years ago.

This change in the bacteria’s metabolic processes happens much faster than structural adaptations.

Insects and weeds are also evolving resistances to chemicals used to control them.

Other Evidence

Fossils – Fossil record is incomplete, but still provides extensive evidence. Paleontologist have traced the evolution of the modern camel. (See page 408 in your text.) 66 million years ago the ancestors of camels were as small as rabbits.

Anatomy Homologous structures – Structural features that

serve different purposes but have a common evolutionary origin. Example: Bones modified for function, but basic arrangement is similar. See the whale forelimb, crocodile forelimb and bird wing on page 409.

More Anatomical Evidence

Analogous structures: Body parts that are similar in function, but do not have common evolutionary origin. These adaptations evolved separately in different groups of organisms. Wings are a good example. (Birds, butterflies, insects)

Vestigial structures: Body structure that has no function but was probably useful to an ancestor. Examples: hind limbs in whale and snake, wings of ostrich, eyes of cavefish

Still More Evidence…

Embryology – Similarities among young embryos suggests evolution from a distant, common ancestor. See the embryos of a fish, a reptile, a bird and a mammal on page 410.They all have tails and gill slits.

Biochemistry – Comparison of DNA or RNA of different species provides biochemical evidence for evolutionary relationships. Scientists use this data to construct evolutionary diagrams (see page 411).