Evolution

Reminder  Read chapter 22  Darwin, Lamarck, Lyell, and Wallace  Resistance to evolution  Pre-Darwin views  On The Origin of Species by Means of Natural Selection

Introduction Evolution – a change in the genetic makeup of a population over time.  Unifying theme of biology  Studied from the molecular to ecosystems level  Relates seemingly unrelated organisms

Overview Variation exists within all populations (mutation, sexual reproduction, conjugation, etc.). Variations in a population are selected for (good) or selected against (bad) depending on the situation. Different populations of the same species are sometimes separated genetically, and are exposed to different circumstances. The variations that are selected for or against may be different for 2 different populations, causing the populations to change differently. If the changes are significant enough new species may occur.

You have already seen the concepts of evolution at work. Visible evolution  Medicine: flu vaccine and antibiotics resistance  Agriculture: hybrid plants and pest resistance  Biotechnology: transgenic organisms

Populations of species are changing. AncestorDescendent

Mechanisms for evolutionary change. Artificial Selection  Commonly called selective breeding.  Selecting organisms with desired traits when breeding livestock, pets, or crops.

Mechanisms for evolutionary change Natural selection Natural conditions (ex. environment and predator) select for favorable characteristics. Over generations, the population will change to favor organisms with traits that make them more fit for their environment.

Evidence for Evolution Biogeography – the geographical distribution of species. – Many islands have species found nowhere else (indigenous). – Closely related species are often found on nearest island mass. – Similar environments on opposite ends of the earth do not have closely related species. – Tropical animals of South America are more closely related to desert animals of South America than Tropical African animals

Evidence for Evolution Comparative Anatomy Forelimbs of closely related animals have similar anatomy (even though they have different functions). These are called homologous structures.

Evidence for Evolution  Fossil record – shows chronological appearance of different species.

Evidence for Evolution Analogous structures – Structures that have the same function, but different structures (ex. Fly wing, bird wing bat wing). Vestigial organs – organs that have no function. – Historical remnants – Ex. Whale has remnants of leg bones, appendix in humans, leg bones in snakes.

Dolphin with legs?

Evidence for Evolution Comparative Embryology Closely related species go through similar developmental stages. Ex. Gill pouches and tail are found in most vertebrates.

Evidence for Evolution Molecular biology – DNA and protein analysis show relationships between species. – Closely related species have similar sequences of bases in DNA and have similar proteins. – Ex. Humans and chimpanzees have 96 – 98% identical DNA. – Humans share less DNA similarities with dogs, and even less with lizards.