Evolution Unit 13 p ,

Darwin and Natural Selection  Beagle Expedition: found unique species that looked similar to species from other parts of the world.  Noticed changes in form among members of the same and closely related species.

Voyage of the HMS Beagle

Darwin’s Voyage

Development of Darwin’s Theory  In 1844, Darwin finally wrote down his ideas about evolution and natural selection in an early outline that he showed to only a few scientists he knew and trusted.  Darwin decided to publish after he received a letter and essay in June 1858 from the young English naturalist Alfred Russel Wallace (1823– 1913), who was in Malaysia at the time. Wallace’s essay described a hypothesis of evolution by natural selection.

Darwin’s Theory Darwin’s theory of evolution by natural selection is supported by four major points: 1.Variation exists within the genes of every population or species. 2.In a particular environment, some individuals of a population or species are better suited to survive and have more offspring. 3.Over time, the traits that make certain individuals of a population able to survive and reproduce tend to spread in that population 4.There is overwhelming evidence from fossils and many other sources that living species evolved from organisms that are extinct.

The Origin of the Species  On The Origin of Species by Means of Natural Selection Nov Charles Darwin  He avoided the term "evolution”  “light will be thrown on the origin of man and his history".  "endless forms most beautiful and most wonderful have been, and are being, evolved."

Natural Selection  Natural selection: mechanism for change in populations that occurs when organisms with favorable variations for a particular environment survive, reproduce, and pass these variations on to the next generation (those with less favorable traits are less likely to survive).

Evolution of Humans  The Descent of Man, and Selection in Relation to Sex Charles Darwin 1871  Darwin outlined sexual selection to explain the evolution of humans

Darwin’s 4 Facts  Exponential Growth of Populations  Variability among species  Factors will prevent Exponential Growth(Steady State)  Traits are inheritable

Darwin’s 2 Inferences  Competition for resources  Individuals most fit for their environment will survive.

4 Tenets of Natural Selection  Individuals tend to produce more offspring than the environment can support.  All populations have genetic variation.  The environment presents challenges to successful reproduction.  Individuals that are better fit their environment tend to live longer, reproduce more, and spread their genes throughout the population.

Natural Selection

Sources of Genetic Variation  Mutation- changes in DNA can slowly introduces new alleles which natural selection helps distribute (can be harmful, beneficial or have no significance)  Meiosis  Random Alignment of chromosomes  Crossing Over- exchange of homologous chromosome segments  Sexual Reproduction- combination of alleles of two individuals  Immigration- incoming alleles to a gene pool

Population Genetics and Evolution  Populations evolve when natural selection causes changes in their allele distribution.  Natural selection causes the greatest changes to populations’ gene pools, but is not the only cause of change  Gene Pool- all the alleles of a population of a species In a population’s gene pool, each allele has a certain frequency which governs the frequency of phenotypes In a population’s gene pool, each allele has a certain frequency which governs the frequency of phenotypes If a population’s allele frequencies do not change, it is not evolving and is said to be in genetic equilibrium If a population’s allele frequencies do not change, it is not evolving and is said to be in genetic equilibrium  Individuals don’t evolve, populations of species do!

Mechanisms for Evolutionary Change  Natural Selection  Artificial Selection  Gene Flow  Genetic Drift  Founder Effect  Genetic Bottleneck

Population Evolution  Artificial selection- a process in which humans consciously select for or against particular features in organisms.  Gene flow-the movement of genes into or out of a population due to interbreeding. Immigration- the flow of alleles into a population. Immigration- the flow of alleles into a population. Emigration-the flow of alleles out of a population. Emigration-the flow of alleles out of a population.

Population Evolution  Genetic drift- the random change of allele frequency in a population, not due to natural selection.  Genetic bottleneck-an event in which the populations’ size is greatly reduced; reduces genetic variability  Founder effect-changes in gene frequency from starting a new population from a small number of individuals; reduces genetic variability.

Adaptations  Structural: Can change the size and/or shape of a body part Can change the size and/or shape of a body part For example: thorns, wings, mimicry (copy the appearance of another species), camouflage (blend in with environment) For example: thorns, wings, mimicry (copy the appearance of another species), camouflage (blend in with environment) Change within a population over time (anywhere from 100 years to millions of years) depending on type of adaptation, rate of reproduction and environmental factors Change within a population over time (anywhere from 100 years to millions of years) depending on type of adaptation, rate of reproduction and environmental factors  Physiological Help populations overcome chemicals they encounter (antibiotics, pesticides, herbicides, etc) Help populations overcome chemicals they encounter (antibiotics, pesticides, herbicides, etc) Develop rapidly (example: bacterial resistance to penicillin) Develop rapidly (example: bacterial resistance to penicillin)

Darwin’s Finches

Evidence for Evolution  Fossil Record  Anatomical relationships  Embryological development  Genetic comparisons

Fossil Record  Fossils can help provide a record for life  However, the fossil record is incomplete - there are large gaps - therefore each and every step of evolution can not be followed  Scientists need to find intermediate species - and once they do, they can provide us with a step by step sequence of evolution

Anatomical Comparisons  Homologous structures Same form, different use Same form, different use Indication of common evolutionary ancestor Indication of common evolutionary ancestor  Vestigial structures Evolutionary remnants of structures that were important in a past ancestor Evolutionary remnants of structures that were important in a past ancestor

Forelimbs of Vertebrates Chapter 13

Evidence of Whale Evolution

Evolutionary Relationship Between Whales and Hoofed Mammals

Embryological Development  There are noted similarities between the embryological development of all vertebrates (fish, chicken, rabbit, human, etc) Presence of gills and tails in all supports evidence that gill-breathing vertebrates preceded air-breathing, terrestrial species Presence of gills and tails in all supports evidence that gill-breathing vertebrates preceded air-breathing, terrestrial species

Comparing Vertebrate Embryo Development

Genetic Comparisons  All living things use DNA.  All living things use the same genetic code.  Can show relationships between species (human and chimpanzee DNA are 99% identical and are closer than chimpanzees are to apes)  Can help reveal when species diverged from their ancestral types

Hemoglobin Comparison Chapter 13

Types of Natural Selection  Stabilizing Selection - favors average traits (average sized spiders fair better than both large and small)  Directional Selection - favors one extreme of a trait (the longer the beak the better)  Disruptive Selection - favors both extremes of a trait (intermediate at disadvantage - often eliminated)

Types of Natural Selection

Evolution of a Species = Speciation  Species = group of organisms that look alike and have the ability to interbreed and produce fertile offspring in nature  Speciation occurs when Interbreeding is prevented Interbreeding is prevented Production of fertile offspring is prevented Production of fertile offspring is prevented

Causes of Speciation  Isolation of populations - Two populations of the same species do not mate because of some form of separation If populations can’t interbreed due to isolation, their allele frequencies can become more and more different from each other If populations can’t interbreed due to isolation, their allele frequencies can become more and more different from each other Each population will adapt to its environment, eventually preventing breeding with members of other populations (reproductive isolation) Each population will adapt to its environment, eventually preventing breeding with members of other populations (reproductive isolation)  Changes in chromosome number causes instantaneous speciation  Most speciation happens gradually

Types of Isolation  Geographic- geographic barriers form that separate two populations.  Ecological- different environmental factors may cause isolation (wet vs. dry, soil conditions, etc.)  Reproductive- mating structures and behaviors may isolate two populations  Temporal- two populations may reproduce at different times

Types of Evolution  Divergence (ex: adaptive radiation); Single populations splits to adapt to different environments Single populations splits to adapt to different environments  Convergence Unrelated species become similar as they adapt to a similar environment. Unrelated species become similar as they adapt to a similar environment. Analogous structures Analogous structures Same use, different formSame use, different form Not evidence of a common evolutionary ancestorNot evidence of a common evolutionary ancestor

Pace of Evolution  Fossil record suggests the rate is variable Gradualism: slow, steady process of change Gradualism: slow, steady process of change Punctuated equilibrium: long periods of genetic stability punctuated by rapid changes to new environmental conditions Punctuated equilibrium: long periods of genetic stability punctuated by rapid changes to new environmental conditions