Evolution

Species Changing over time

Charles Darwin

• Evolution by Means of Natural Selection

Reasons for Change

• MutationA mutation could cause parents with genes for bright green coloration to have offspring with a gene for brown coloration. That would make the genes for brown beetles more frequent in the population.

• MigrationSome individuals from a population of brown beetles might have joined a population of green beetles. That would make the genes for brown beetles more frequent in the green beetle population.

Reasons for Change• Genetic Drift

Imagine that in one generation, two brown beetles happened to have four offspring survive to reproduce. Several green beetles were killed when someone stepped on them and had no offspring. The next generation would have a few more brown beetles than the previous generation—but just by chance. These chance changes from generation to generation are known as genetic drift.

Natural SelectionImagine that green beetles are easier for birds to spot (and hence, eat). Brown beetles are a little more likely to survive to produce offspring. They pass their genes for brown coloration on to their offspring. So in the next generation, brown beetles are more common than in the previous generation.

Natural Selection Principles

• Principle of overproduction: Organisms are capable of producing huge numbers of offspring

• Principle of variation: offspring have hereditary physical variations in phenotype & genotypes

• Principle of competition: offspring must compete for limited resources

• Principle of differential reproduction: Organisms whose phenotypic characters allow them to best compete for limited resources will leave the most genes to succeeding populations.

Artificial Selection• Long before Darwin, farmers and breeders used the idea of

selection to cause major changes in the features of their plants and animals. Farmers and breeders allowed only the plants and animals with desirable characteristics to reproduce, causing the evolution of farm stock. This process is called artificial selection because people (instead of nature) select which organisms get to reproduce.

• As shown here, farmers have cultivated numerous popular crops from the wild mustard, by artificially selecting for certain attributes.

Genetic Variation

• Mutations are changes in the DNA. A single mutation can have a large effect, but in many cases, evolutionary change is based on the accumulation of many mutations.

• Gene flow is any movement of genes from one population to another and is an important source of genetic variation.

• Sexual reproduction can introduce new gene combinations into a population.

Survival of the fittest!

• Those individuals best suited to exploiting the various factors of the environment will, by definition, leave more genes to succeeding generations than those that are less suited for their environment!

Speciation

• Geographic isolation is a common way for the process of speciation to begin: rivers change course, mountains rise, continents drift, organisms migrate, and what was once a continuous population is divided into two or more smaller populations, but it doesn’t even need to be a physical barrier like a river that separates two or more groups of organisms—it might just be unfavorable habitat between the two populations that keeps them from mating with one another.

Types of evolutionConvergent, divergent, co-evolution

Coevolution is likely to happen when different species have close ecological interactions with one another. These ecological relationships include:– Predator/prey and

parasite/host – Competitive species – Mutualistic species

This is the product of coevolution: the plants would not have evolved hollow thorns or nectar pores unless their evolution had been affected by the ants, and the ants would not have evolved herbivore defense behaviors unless their evolution had been affected by the plants.

• Divergent evolution is the process of two or more related species becoming more and more dissimilar.

In convergent evolution, on the other hand, unrelated species become more and more similar in appearance as they adapt to the same kind of environment.

Tree of Life

Cladogram

Phylogenic tree

Dating!!!

•  1. Radiometric dating relies on half-life decay of radioactive elements to allow scientists to date rocks and materials directly.

•  2. Stratigraphy provides a sequence of events from which relative dates can be extrapolated.

•  3. Molecular clocks allow scientists to use the amount of genetic divergence between organisms to extrapolate backwards to estimate dates.

Fossil recordHave many good fossil records to show evolutionary relationships of organisms. Not complete for all species because of the process of becoming a fossil.

Whales

Cats

Archaeopteryx

Anatomy

Analogous Structures : a structure that serves the same function in two species, but is NOT derived from a common ancestral structure

Homologous Structures: a structure that serves different functions in two species, but is derived from a common ancestral structure

vestigial structures have marginal, if any use to the organims

Embryology

Which of these is the human???

A B C D E F G H

Embryology

Biochemical evidence

Cell Membranes are similar in all living organisms

ALL DNA in prokaryotes & eukaryotes is made of A, G, T, C

There are only 20 amino acids that make up all of the proteins needed to make EVERY living thing on the planet

ATP is the fuel for ALL living cells!

Human Evolution It is important to

remember that:• Humans did not evolve

from chimpanzees. Humans and chimpanzees are evolutionary cousins and share a recent common ancestor that was neither chimpanzee nor human.

• Humans are not “higher” or “more evolved” than other living lineages. Since our lineages split, humans and chimpanzees have each evolved traits unique to their own lineages.