Ch. 6.3 Biological Evidence of Evolution

1. What evidence from living species supports the theory of evolution?

2. How are Earth’s organisms related?

Focus Questions

• As fossils were discovered, patterns emerged that showed many different species with similar body structures.

• Evidence suggests that species change over time.

• Evolution (to evolve) = Change in species over time

What causes species to change over time?

• The fossil record is evidence that horses descended from organisms for which only fossils exist today•The degree to which species are related depends on how closely in time they diverged, or split, from their common ancestor.

• Although the fossil record is incomplete, it contains many examples of fossil sequences showing close ancestral relationships.• The fossil record indicates that different species of horses often overlapped with each other – not in a series of orderly steps.

• Comparative Anatomy – the study of similarities and differences among structures of living species.

• Homologous Structures – body parts are similar in structure, but different in function

Comparative Anatomy

The forelimbs of these species are different sizes, but their placement and structure suggest common ancestry.

Evidence: More similar structures = more related species (evolved from common ancestor)

Analogous structures: Body parts are similar in function, but different in structure (not closely related)

(ex: bird wings vs. insect wings)

Comparative Anatomy

Evidence: Differences in structures = species are not closely related

Vestigial structures are body parts that have lost their original function through evolution.

Comparative Anatomy

Section 1 Change over Time

Evidence: shows relation to ancestors who used the part for a specific purpose

Studying the development of embryos can also provide scientists with evidence that certain species are related.

Embryology – The study of the development of embryos from fertilization to birth

Evidence: similar embryo development = more closely related

Developmental Biology

All vertebrate embryos exhibit pharyngeal pouches at a certain stage of their development.

In reptiles, birds, & humans, pharyngeal pouches develop into a gland in the neck – in fish, they form gills. (both glands & gills regulate calcium)

2. How are Earth’s organisms related?

Rat Chicken Human

• Molecular biology is the study of gene structure and function.

• Discoveries in molecular biology have confirmed and extended much of the data already collected about the theory of evolution.

• Comparing DNA Sequences: Scientists compare the similarity of genes (DNA) & proteins to study the relatedness of living species.

Molecular Biology

Aligned DNA fragment and first chromosome banding patterns for man (Homo sapiens), chimpanzee (Pan troglodytes), gorilla (Gorilla gorilla), and orangutan (Pongo pygmaeus).

Evidence: more similar the DNA = more related the species

Divergence: Using the rate of DNA mutations (“molecular clock”) to estimate when species changed

Molecular data indicate that whales and porpoises are more closely related to hippopotamuses than they are to any other living species.

Molecular Biology

~55

Evidence: shows how long ago species diverged from a common ancestor

• The fossil record is still incomplete, but new fossils are being discovered all the time.

• For example, the Tiktaalik fossil has both fish and amphibian features – linking the 2.

• Most evolution research is now done at the molecular level, but Darwin’s basic principles still hold true after 150+ years.