Charles Darwin ( ) Not the first to Propose a Theory of Evolution – He had the data (so did Wallace) – Studied geology – Understood “Artificial” selection – He was Wealthy 1

The Voyage of the Beagle ( ) Darwin was a Naturalist – Career Opportunity

Galapagos Islands “New” Volcanic Islands – Animals are Unique (Why?) – Some resemble South American species – Similar Islands have different species (Why?)

Change Over Time Animals go extinct! – Causes for extinction? – Can new ones emerge?

Adaptation to Environment

LaMarckian Theory Jean-Baptiste Lamarck ( ) – Believed that traits were changing according to biological mechanisms, but.. – Traits were acquired as a result of a parent’s struggles.

There is a Simpler Explanation Offspring are diverse They struggle to survive (some die) The environment (nature) takes care of the rest

Thomas Robert Malthus ( ) Populations outgrow resources Someone is always dying That’s Nature’s Way Stop feeding the hungry

Thomas Robert Malthus ( ) That the increase of population is necessarily limited by the means of subsistence, That population does invariably increase when the means of subsistence increase, and, That the superior power of population is repressed, and the actual population kept equal to the means of subsistence, by misery and vice.

Darwin didn’t “discover” as much as he assembled existing pieces (1859).

Then, he described (mostly nonhuman) Sex…

…and emotions…

…and child development.

Summary Darwin developed a theory of natural selection and “species origins” based on (1) diverse traits and (2) natural selection for those traits. He recognized “traits” as being both physical features (widely accepted as adaptations) and behaviors (not so widely accepted).

Subsequent Reaction Darwin was honest about what he didn’t understand. – He had no mechanism of inheritance – Offspring were varied and not “averages” of their parents – For almost 50 years, Darwin’s theory was in the category of “seems to make sense,” but Natural Selection was not seen as primary driver of change. The story felt incomplete.

The Modern Synthesis Geregor Mendel ( ) – Working with pea plants Reproduction is easier to control – Described Mendelian Genetics Dominant and recessive traits Multiple genes could exist in a population but each individual only carried two Wilhelm Johannsen ( ) – Coined “gene, genotype, phenotype” – Promoted the significance of M.G.

Chromosomal Replication Mitosis and Meiosis – Walter Fleming ( ) – August Weismann ( ) Offspring come from “germ cells” not “somatic cells” – Splitting explains a mechanism for Mendelian Genetics Germ cells do not “learn” from what the parent does – Lamarck was wrong!

Mendel and Meiosis (~1910) Discoveries of other Mendelian traits. – Human Examples: Wet (dominant) or dry (recessive) earwax, Albinism (recessive), Blood type, several cancers, Huntington's disease, Lactase persistence (dominant), Sickle-cell disease Explained sex-linked traits and pointed to chromosomes as carriers of the “genes” Imperfect copying could lead to mutations – New genes could be good, most were probably bad

Population Genetics Genes are carried in populations, not just individuals, and there are many reasons why more than one (or two) genes can persist. – Evolution can “tolerate” multiple genes The Hardy-Weinberg model explains a way to predict the proportion of two (Mendelian) genes in a population during a period of stability with no selective pressure.Hardy-Weinberg Sex ratios are balanced by external forces Sex ratios

Microbiology and Symbiosis The genetic evidence for common ancestry

Fossil Discoveries Evidence for the speed of change

Human Paleontology Is the missing link missing? – Chimpanzees are our closest relatives (DNA supports this), though fossils from a specific common ancestor (6 mya)have not been found. There are many examples of human ancestors

The Modern Synthesis All the pieces fit and support Darwin’s Natural Selection theory. The modern synthesis bridged the gap between the work of experimental geneticists and naturalists, and paleontologists. It states that:

The Modern Synthesis Evolution is consistent with known genetic mechanisms and the observational evidence from field research. Evolution is gradual: small genetic changes regulated by natural selection accumulate over long periods and many genes can “drift” through a population at a given time. Discontinuities amongst species (or other taxa) are explained as originating gradually through geographical separation and extinction. Paleontology helps here. Natural selection is the main mechanism of change; even slight advantages are important. The object of selection is the phenotype in its surrounding environment. The role of genetic drift (random fluctuations in gene frequency) is equivocal.

Summary For more than a century after Darwin’s Origin, most psychologists viewed almost all behaviors – especially human behaviors - as learned. Evolutionary Psychologists regard behavior as a combination of learned adaptations that emerge in a lifetime and inherited adaptations that emerged long ago.