EVOLUTION

Natural Selection• Mechanism for evolution• Differential survival and reproduction of

chance inherited variants, depending on environmental conditions

Variation in Traits

Differential Reproduction

Heredity of the more advantageous traits

EVOLUTION by Natural Selection

Biological adaptations include changes in structures, behaviors, or physiology that enhance survival and reproductive success in a particular environment

EVOLUTIONWhere is the Proof?

Evidence for Evolution• What direct evidence supports this theory?– Changes in populations over time• Ex: peppered moth

Evidence for Evolution• What direct evidence supports this theory?– Structural adaptations• Ex: mimicry; camouflage

Evidence for Evolution• What direct evidence

supports this theory?– Physiological changes• Ex: drug-resistant

bacteria;• Ex: pesticide-resistant

insects

E V I D E N C E• Biogeography– Study of the past and present geographical distribution

of species• The Fossil Record– Succession of fossil forms is compatible with what is

known from other types of evidence and the major branches of descent in the tree of life

• Comparative Anatomy• Comparative Embryology• Molecular Biology

The Fossil Record• Remains of animals and plants

found in sedimentary rock deposits give us an indisputable record of past changes through time.

• This evidence attests to the fact that there has been a tremendous variety of living things.

• Some extinct species had traits that were transitional between major groups of organisms.

Their existence confirms that species are not fixed but can evolve into other species over time.

Comparative Anatomy

• Homology- similarity in characteristics resulting from a shared ancestry

• Homologous Structures- structures in different species that are similar because of common ancestry

Homologies• Homologies and the

tree of life are important in explaining ancestry.

• Homologies shared by a greater number of species are likely to have evolved earlier on in history and are further down on the tree of life.

Homologies• Homologies that have evolved more recently

are seen on only small branches of the tree.– Example: tetrapods--the vertebrate branch

consisting of birds, amphibians, mammals and reptiles. • They all have the same 5-digit limb structure which

indicates these mammals all share a common ancestor.

5 Digits

Homologies• Forelimbs of all mammals show the

same arrangement of bones from shoulder to finger tip.

• These occur even if the structure is used for a completely different function.

• These anatomical differences would not have arisen in a new species if they did not share a common ancestor.

ARM = carrying Front Leg = walking Front Flipper = swimmingWING = flying

Humerus

Radius & Ulna

Carpals

Metacarpals

Phallanges

Homologous Structures:BONES

A Biogeographical Example:Homologous vs Analogous

• Eutherians (placental) vs. Marsupials

• Both of these are a type of flying squirrel, but are unrelated and distinctly different from one another.

• Marsupials are born as embryos and develop in the mother’s pouch.

• Eutherians develop completely within the uterus of the mother.

A Biogeographical Example:Homologous vs Analogous

• Although the two mammals look similar and occupy similar niches, the resemblance is not homologous--it’s analogous and the result of convergent evolution.

Homology vs. Analogy

Other Similarities Revealed• Comparative embryology– Compares structures seen early on in

development--pharyngeal pouches for example.– Ontogeny Recapitulates Phylogeny

• Vestigial organs– Organs with little or no use remaining from

ancestral lineages• Some snakes have vestiges of legs bones and a pelvis• Coccyx in humans (tail)

Comparative Embryology

Lizard Tortoise Pig Human

Comparative Embryology

Homologies• Molecular homologies exist as well--the

genetic machinery of DNA and RNA also points to a common ancestor– the existence of Hox genes in development.• Genes and proteins with sequences of monomers that

match indicate that the sequences must have been copied from a common ancestor

Homework

• Explain, using examples, how the fossil record, comparative anatomy, and other evidence supports the theory of evolution.

–At least one page, typed, double-spaced, & sources of info/pics cited.