Scientific evidence to support the Theory of Evolution by Natural Selection

Trilobite fossil found in Burgess Shale

• FOSSILS – are the mineralized remains or traces (tracks, imprints) of animals, plants or other organisms

• THE FOSSIL RECORD –fossils found in rock strata that show a sequence or history of life on Earth

Some of the fossils found here are now long extinct and are unlike anything presently existing

• The Burgess Shale is a middle Cambrian site (~540 MYA)

• One of the few places in the world where difficult-to-preserve soft-bodied organisms of our past were preserved

• Fossils found in young layers of rock (ie closer to the surface) tend to be more similar to present day organisms

• Fossils appear in chronological order (oldest ancestors in deepest layers

• Not all organisms appear in the fossil record at the same time – ie fish are the oldest vertebrates – then in subsequent layers amphibians, reptiles, mammals and birds

Archaeopteryx – a transitional fossil because of its characteristics of both reptiles (dinosaurs) and birds

• Transitional fossils are fossils that show intermediary links between groups of organisms

• They can provide a link between the past and present

ARCHAEOPTERYX – transitional fossil

• Example: Basilosaurus and Dorudon were ancient whales with tiny hind limbs – living entirely in water

• Ambulocetus – a more recent ancestor, had heavier leg bones and lived in both water and on land

- The tiktaalik was an ancient tetrapod- It was thought to have descended from lobe-finned fishes

-- They lived in oxygen-poor water - used their lobe fins to live partly on land-possibly gave rise to amphibians

ADAPTIVE RADIATION – Diversification of a common ancestral species into a variety of species

• Darwin and Wallace observed that many species evolve in one location and spread out to other areas

• Darwin found 14 different species of finch – he theorized

all evolved from one common ancestral finch

-left: cactus from S.America-right: cactus from Australia

Top: Canary Island lizardBottom: West African lizard

-a depiction of the Earth 250 MYA – continents were joined together

• Fossils of the same species can be found on the coastline of neighbouring continents

• Example: Cynognathus has been found in Africa and S.America

• At one time, all continents were joined (Pangea – 250 MYA)

-distribution of ancient organisms Cynognathus crateronotus

HOWEVER: they ALL contain the same set of bones organized in similar ways – WHY?

Homologous structures are similar in structure but often differ in function

Vertebrate forelimbs

can be used for many different functions:

• Flying (birds, bats)• Swimming (whales)• Brachiation

(monkeys)• Running-horses,dogs

Homologous structures provide evidence for a common ancestor amongst all vertebrates

Analogous StructuresStructures that evolve separately to perform a similar function are analogous. The wings of birds, bats, and insects, for example, have different embryological origins but are all designed for flight.

•Bird: feathers•Bat: skin•Butterfly: chitin

VESTIGIAL STRUCTURES

• Vestigial structures

are thought to have

had a purpose at

one time in our

ancestry, but no

longer have a

specific function

(eg) human appendix

VESTIGIAL STRUCTURES

• “c” indicates the

Underdeveloped hind legs

Of the baleen whale

• The muscles connected to the ear of a human do not develop enough to have the same mobility as those of the monkey

- Similarities among embryos point to a common ancestor

• The embryos of different vertebrates show similar stages of embryonic development

• Neck pouches – in humans become ears & throat

- in fish become gills

Can you tell which embryo is which?

A – cat C - horseB – cow D - human

The DNA of chimpanzees & humans is ~ 98% identical

• Many organisms share similar cellular components such as:

• Proteins – long chains of amino acids used for

building & repair• Enzymes – made from

proteins – they control many biochemical reactions in the cell

• DNA – genetic material found in the nucleus

http://adsabs.harvard.edu/abs/1999AmSci..87.....H

hemoglobin (found in RBCs) is used to bond to O2

• Hemoglobin—the oxygen-transport protein that gives blood its red color—got its start at about the time life originated on earth, nearly four billion years ago. Now it is almost ubiquitous, appearing in the cells of plants, animals and even bacteria, and a study of this protein affords scientists a rare glimpse back as well as forward in time. A look at the ancestral hemoglobins indicates that newly arising proteins co-opt the chemistry of older ones and gain new functions through structural alterations. But these studies have revealed an additional way to modify function. Scientists are coming to the realization that changes in a protein's regulation—the when and how of its expression—can also give rise to functional differences. The surprise, says the author, is that these regulatory changes outpace structural ones—an important lesson for students of molecular evolution and a possible indicator of where protein evolution will go in the future.

Above: Hominid evolution