Evidence of Evolution by Natural Selection

Evidence of Evolution A. Fossil record B. Anatomical record transition species B. Anatomical record homologous & vestigial structures embryology & development C. Molecular record protein & DNA sequence D. Artificial selection human-caused evolution

A. Fossil record Layers of sedimentary rock contain fossils new layers cover older ones, creating a record over time fossils within layers show that a succession of organisms have populated Earth throughout a long period of time

Fossil Record

Fossil record A record showing us that today’s organisms descended from ancestral species

Evolutionary change in horses 550 500 450 Equus 400 350 Body size (kg) 300 250 Merychippus increase in size, loss of toes, increase in size of molars 20-25 mya grasslands became widespread in Norh America molars = easer to eat grass hoof = faster locomotion on grassland 200 Mesohippus 150 Hyracotherium 100 50 Nannippus 60 55 50 45 40 35 30 25 20 15 10 5 Millions of years ago

Evolution of birds Archaeopteryx lived about 150 mya links reptiles & birds The avian nature of the brain and inner ear of Archaeopteryx (Alonso et al. 2004) - Archaeopteryx, the earliest known flying bird from the Late Jurassic period, exhibits many shared primitive characters with more basal coelurosaurian dinosaurs (the clade including all theropods more bird-like than Allosaurus), such as teeth, a long bony tail and pinnate feathers. However, Archaeopteryx possessed asymmetrical flight feathers on its wings and tail, together with a wing feather arrangement shared with modern birds. This suggests some degree of powered flight capability but, until now, little was understood about the extent to which its brain and special senses were adapted for flight. Alonso et al. (2004) investigated this problem by computed tomography scanning and three-dimensional reconstruction of the braincase of the London specimen of Archaeopteryx. A reconstruction of the braincase and endocasts of the brain and inner ear suggest that Archaeopteryx closely resembled modern birds in the dominance of the sense of vision and in the possession of expanded auditory and spatial sensory perception in the ear. Alonso et al. (2004) concluded that Archaeopteryx had acquired the derived neurological and structural adaptations necessary for flight. An enlarged forebrain suggests that it had also developed enhanced somatosensory integration with these special senses demanded by a lifestyle involving flying ability. Smithsonian Museum, Washington, DC

2006 Fossil Discovery of Early Tetrapod Tiktaalik “missing link” from sea to land animals

Evolution of whales http://www.pbs.org/wgbh/evolution/library/03/4/l_034_05.html

B. Anatomical record 1. Homologous structures similarities in characteristics resulting from common ancestry

Homologous structures Similar structure Similar development Different functions Evidence of close evolutionary relationship recent common ancestor

Homologous structures spines leaves succulent leaves tendrils needles colored leaves

Separate evolution of structures 2. Analogous structures Separate evolution of structures similar functions similar external form different internal structure & development different origin no evolutionary relationship Solving a similar problem with a similar solution

3. Vestigial organs Modern animals may have structures that serve little or no function remnants of structures that were functional in ancestral species deleterious mutations accumulate in genes for non-critical structures without reducing fitness snakes & whales — remains of pelvis & leg bones of walking ancestors eyes on blind cave fish human tail bone

Vestigial organs Hind leg bones on whale fossils

4. Comparative embryology Similar embryological development in closely related species all vertebrate embryos have similar structures at different stages of development gill pouch in fish, frog, snake, birds, human, etc.

C. Molecular record(biochemical) Comparing DNA & protein structure universal genetic code! DNA & RNA compare common genes cytochrome C (respiration) hemoglobin (gas exchange) 25 50 75 100 125 Millions of years ago Horse/ donkey Sheep/ goat Goat/cow Llama/ cow Pig/ Rabbit/ rodent Horse/cow Human/rodent Dog/ Human/ Human/kangaroo Nucleotide substitutions Closely related species have sequences that are more similar than distantly related species DNA & proteins are a molecular record of evolutionary relationships

Comparative hemoglobin structure Human Macaque Dog Bird Frog Lamprey 8 32 45 67 125 10 20 30 40 50 60 70 80 90 100 110 120 Number of amino acid differences between hemoglobin (146 aa) of vertebrate species and that of humans

D. Artificial selection Artificial breeding can use variations in populations to create vastly different “breeds” & “varieties” “descendants” of wild mustard “descendants” of the wolf

Patterns of Evolution 1. Convergent evolution Flight evolved in 3 separate animal groups evolved similar “solution” to similar “problems” analogous structures

Convergent evolution Fish: aquatic vertebrates Dolphins: aquatic mammals similar adaptations to life in the sea not closely related

2. Parallel Evolution Convergent evolution in common niches marsupial filling similar ecological roles in similar environments, so similar adaptations were selected but are not closely related marsupial mammals placental mammals

3. Adaptive Radiation or Divergent Evolution 2 or more related species become farther apart in their similarities. As each adapts to a new environment they become more dissimilar in their appearance they become. Example: Darwin’s finches

Building “family” trees Closely related species (branches) share same line of descent until their divergence from a common ancestor

Natural selection in action Insecticide & drug resistance insecticide didn’t kill all individuals resistant survivors reproduce resistance is inherited insecticide becomes less & less effective The evolution of resistance to insecticides in hundreds of insect species is a classic example of natural selection in action. The results of application of new insecticide are typically encouraging, killing 99% of the insects. However, the effectiveness of the insecticide becomes less effective in subsequent applications. The few survivors from the early applications of the insecticide are those insects with genes that enable them to resist the chemical attack. Only these resistant individuals reproduce, passing on their resistance to their offspring. In each generation the % of insecticide-resistant individuals increases.