Chapter 4 Evolution & Biodiversity

1 billion years of chemical change to form the first cells, followed by about 3.7 billion years of biological change.

Mutations, random changes in the DNA of a cell, can occur at any time These small changes have provided the means for genetic variability How have these small changes in a single organism’s DNA led to the abundant amount of biodiversity that exists today? Natural Selection

According to Charles Darwin, natural selection is a biological mechanism for evolution. Some organisms have particular traits, or genes that give them an increased chance for survival in their environment. They are more likely to reproduce more often than other organisms lacking these genes

Those will increase the percent of the population who express this successful trait Any organism that is better suited for their environment will be fit to reproduce and pass down the favorable trait The genetically inheritable traits that make an organism more likely to survive and reproduce are adaptations

Adaptations lead to differential reproduction because they will leave more offspring than other individuals in the population

Natural Selection and Adaptation: Leaving More Offspring With Beneficial Traits Three conditions are necessary for biological evolution: 1. Genetic variability 2. traits must be heritable, 3. trait must lead to differential reproduction. An adaptive trait is any heritable trait that enables an organism to survive through natural selection and reproduce better under prevailing environmental conditions

Why won’t our lungs evolve to deal with air pollution? Limits to adaptation: A change in the environment can only lead to adaptation for traits already present in the gene pool Reproductive capacity may limit a population’s ability to adapt If you reproduce quickly (insects, bacteria) then your population can adapt to changes in a short time If you reproduce slowly (elephants, tigers, corals) then it takes thousands or millions of years to adapt through natural selection Most individuals without trait would have to die in order for the trait to predominate and be passed on

How Can Geologic & Climatic Events Impact Natural Selection Environmental Changes can cause differential reproduction to stop Geologic Events like tectonic activity, movement of continents, earthquakes and volcanoes. Climatic events= Periods of warming and cooling (ice ages) have shaped earth’s ecosystems. Organisms unable to adapt to changing conditions have become extinct and replaced with organisms better suited for the new environment

How do New Species Evolve? Geographic Isolation= Geological and climatic events can physically separate populations for long periods of time. Since these populations are exposed to different environmental pressures, the traits that make one population successful will not make the other successful.

This causes reproductive isolation These types of isolation events can lead to one species into evolving into two distinct species= speciation event When an entire organism disappears from earth its known as extinction Mass extinctions have opened ecological roles or niches

A niche is an organisms way of life including everything that would effect its survival and reproduction Generalist Species= have broad niches Specialist Species= have narrow niches