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EVOLUTION AND NATURAL SELECTION. Evolution is defined as the change in species over time. Darwin theorized that evolution occurs through a process known as natural selection . This process is broken down into four parts:. Overproduction Genetic Variation Struggle to Survive

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evolution and natural selection
EVOLUTION AND NATURAL SELECTION

Evolution is defined as the change in species over time. Darwin theorized that evolution occurs through a process known as natural selection. This process is broken down into four parts:

  • Overproduction
  • Genetic Variation
  • Struggle to Survive
  • Successful Reproduction
overproduction
OVERPRODUCTION

Overproduction is a process in which each species produces more offspring than will survive to maturity.

genetic variation
GENETIC VARIATION

The individuals in a population are slightly different from each other. Each individual has a unique combination of traits, such as color, size, speed, and the ability to find food. Some traits increase the chances

of survival and

reproduction.

These beneficial traits

are called adaptations.

Variations are

genetic and can be

inherited.

struggle to survive
STRUGGLE TO SURVIVE

Because there is only so much food, water, space, and other resources available in the environment, not all individuals will

live to adulthood.

Those best adapted will

have a better chance of survival. Nature, or the environment selects

which organisms live

and which die. This

struggle is often referred

to as “Survival of the Fittest”.

successful reproduction
SUCCESSFUL REPRODUCTION

The individuals that are well adapted to their environment, that is, those that have better traits for living in their environment,

are more likely to survive and reproduce. Their

traits are thereby passed

on to their offspring. Theindividuals that are not well adapted to their environment are more likely to die early or produce few offspring.

natural selection in action
NATURAL SELECTION IN ACTION

When an effective insecticide is used on a population of insects, most insects are killed, but few may survive. These survivors have genes that make them resistant to the

insecticide.

natural selection in action7
NATURAL SELECTION IN ACTION

The survivors then reproduce, passing the insecticide-resistant genes to their offspring.

natural selection in action8
NATURAL SELECTION IN ACTION

In time, the replacement population of insects is made mostly of individuals that have the insecticide-resistant genes.

natural selection in action9
NATURAL SELECTION IN ACTION

Ultimately, when the same kind of insecticide is used on the insects, only a few are killed because

the overall population hasbecome resistant to that insecticide.

how does evolution really work
How Does Evolution Really Work?

Select Video 4 and travel to Ecuador to see how the process of natural selection operates in populations of rainforest hummingbirds.

evidence of evolution
EVIDENCE OF EVOLUTION

There are five pieces of evidence scientist use to support the theory of evolution. They are:

  • The Fossil Record
  • Homologous Structures
  • Vestigial Structures
  • Embryonic Structures
  • DNA Evidence
the fossil record
THE FOSSIL RECORD
  • Fossils are the preserved remains or traces of an organism that lived in the past. The millions of fossils that scientists have collected, is called the fossil record.
the fossil record13
THE FOSSIL RECORD
  • According to the fossil record, over 90% of the organisms that once lived on the Earth are now extinct. In addition, there is no fossil evidence that organisms alive today were here long ago. However, the organisms alive today have features that resemble life of the past. What happened to the species that lived long ago, and where did the life of today come from? The evolutionist explanation is that species from long ago have changed into the species alive today.
homologous structures
HOMOLOGOUS STRUCTURES

Scientists have observed that many different organisms have structures that are quite similar. For instance, when comparing a human hand, cat leg, dolphin flipper, and a bat wing, we find nearly identical bone patterns.

Why would structures specialized for such different functions such as grasping, walking, swimming and flying be so similar? The evolutionist conclusion is that these different animals must have evolved from a common ancestor.

vestigial structures
VESTIGIAL STRUCTURES

Vestigial structures are structures that no longer serve a function in the living organism. For instance, humans have a tail bone that serves no apparent function. In addition, the modern whale has a series of bones near the base of the skeleton that resemble hip bones. Hip bones serve the function of allowing land animals to walk. Why would a whale have hip bones? The evolutionist conclusion is that the whale must haveevolved from a land walking creature.

vestigial structures16
VESTIGIAL STRUCTURES

Fossil evidence also supports the theory that the modern day whale evolved from a land walking animal.

50 Million Years Ago

55 Million Years Ago

46 Million Years Ago

40 Million Years Ago

how do we know evolution happens
How Do We Know Evolution Happens?

View Video 3 to see how different lines of

evidence contribute to our picture of

evolution. Learn about the fossil evidence for

whales' land-dwelling ancestors.

embryonic stuctures

A developing baby is called an embryo. Embryos of very different organisms such as a chicken, rabbit, and human have embryos that look nearly identical. During the early stages of development, all have a tiny tail and gill slits in their throats. The conclusion is that all of these organisms have a common

EMBRYONIC STUCTURES

ancestor. It is thought that the embryo is like a window through evolutionary time. The ancestors of these species once had tails and gills.

dna evidence

The DNA that codes for all life on this planet is composed of the same four nitrogen bases, adenine, guanine, cytosine, and thymine. In addition, this coded message creates the same twenty amino acids that builds all life forms on the planet. This similarity, according to the theory of evolution, suggests that all life on the planet has evolved from a common ancestor.

DNA EVIDENCE
molecular evidence for evolution
Molecular Evidence For Evolution

Select Video 5 and examine the fossil and molecular evidence that supports the evolution of humans from earlier primate ancestors.