Traits

*** A trait is a distinguishing characteristic of an organism:

• Basically what makes it unique.

• Traits are inherited from the parents

• A generation is a group of individuals born and living at the same time; the time span between the birth of parents and the birth of their children.

** All populations – all the organisms of the same species that live in the same area at the same time – that reproduce sexually contain differences, or variations, in some characteristics of their members.

• Asexual reproduction has no differences or ‘card shuffle’. It’s essentially cloning.

*A variation is a slight difference in an inherited trait among individual members of a species.

*Variation creates diversity in the population. Variation in organisms occurs due to the random changes to the genetic material of the offspring.

Effects of Variations

Some variations might harm an organism’s chances of survival.

*One example is albinism. This results in an animal being all white. It is caused by a random change to genetic material. This trait can be especially harmful to animals that are prey because their predators can easily spot them!

Some random genetic changes cause no harm and can be beneficial.

• Like the spots on a giraffe helps camouflage.

• A variation might make an organism better able to find food, avoid predators, or reproduce more successfully. OR… It might make no difference.

*** EXAMPLES:

Marine birds have genetic variations that make some better at getting food & resisting disease. Some of these birds have feet that are different shades of blue.

• Foot color indicates how healthy they are.

• Females will select males with brighter blue feet.

  • These birds are healthier.

  • They will produce stronger offspring.

  • Health makes them desirable as a mate. The trait of bright blue feet is desirable. It helps the genes carry on.

Over generations, as more and more offspring are born with the beneficial variation, the occurrence of the variation increases.

 IT BECOMES A TRAIT OF THE POPULATION

Charles Darwin

***Charles Darwin was an English naturalist who proposed the theory of biological evolution by Natural Selection.

Darwin worked to explain how and why traits in populations change over time

He spent many years observing plants and animals in their natural habitats before developing his theory.

• Darwin’s theory of natural selection.

• His theory was about changes to populations of organisms over time.

• A scientific theory is an explanation of the natural world that is well supported by evidence.

** Darwin served as a naturalist on the HMS Beagle, a survey ship of the British navy.

**During his voyage around the world, Darwin observed & collected many plants & animals.

***Darwin was especially interested in the organisms he saw on the Galapagos Islands.

• The islands are located off the South American coast in the Pacific Ocean.

• Darwin observed that each island had a slightly different environment.

  • Some were dry.

  • Some were more humid.

  • Others had mixed environments.

• Giant tortoises lived on many of the islands.

• When a resident told Darwin that the tortoises on each island looked different, he became curious.

  • Darwin wanted to understand how one group of organisms can be different yet have the similar traits.

Note that the tortoises evolved based on the food available on their respective islands.

Domed tortoises had low vegetation so they had short necks.

Intermediate tortoises had a range of vegetation heights so they had intermediate necks.

Saddleback tortoises had high vegetation so they had long necks.

Darwin’s Theory

Darwin observed slight variations in the traits of the animals on different islands.

***He realized there was a relationship between species & the food sources of the islands on which they lived.

*Some tortoises had long necks & a large space between the shell and neck.

~ They lived on islands with tall cacti.

~Their unique necks and shells helped them reach high to eat the cacti.

*Some tortoises had short necks and shells close to the neck.

~They lived on islands with plenty of short grass.

*Each species of tortoise was specialised, or suited, for living in a particular environment.

THIS IS NATURAL SELECTION!

*Later, he was surprised to learn that many of these varieties were different enough to be separate species.

Common Ancestors

Darwin became convinced that all the tortoise species were related. He thought they shared a common ancestor. The suspected that a storm had carried a small tortoise population to one of the islands millions of years ago. 

*They had come from South America. Eventually, the tortoises spread to the other islands. Over many generations, each island’s tortoise population developed differently.

• Their neck length and shell shape made it easier to access their island’s food source.

***Remember, competition is the demand for resources, such as food, water, and shelter in short supply in a community. Not everybody gets the resources. Suitable traits help survival.

Darwin realized that variations were the key to the puzzle of how populations of tortoises and other organisms evolved.

*** Darwin understood that food is a limiting resource.

This means that food on each island environment could not support every tortoise that was born. Tortoises had to compete for food.

*As the tortoises spread to the different islands, some were born with random variations in neck length and shell shape. Some variations benefited a tortoise.

• They allowed it to compete for food better than other tortoises.

• So the tortoise lived longer.

• Because it lived longer, it reproduced more.

It passed on its variation to its offspring.

*Natural selection is the process by which organisms with variations that help them survive in their environment live longer, compete better and reproduce more than those that do not have the variations.

*** Natural selection explains how populations change over many generations. They change as their environments change.

Natural selection explains the process by which Galapagos tortoises became matched to their food sources.

Artificial Selection

You read about the process of natural selection. You read that the traits in populations can change over generations. Through this process, random changes to genetic material that help organisms survive accumulate over time. The variations become traits in a population. These provide evidence of how closely Earth’s species match their environments. This is what Darwin predicted in his theory of evolution by natural selection. Darwin provided many examples of changes to traits in populations by natural selection. He wrote a book to explain his theory, ON THE ORIGIN OF SPECIES. Darwin didn’t write it until 20 years after he developed his theory. He spent those years collecting more evidence to support his theory of evolution by natural selection. He studied barnacles, orchids, corals, & earthworms. 

***As a hobby, Darwin selectively bred pigeons of different colors & shapes. ➡ ➡ ➡ ➡

He produced new, fancy varieties. Darwin called this process artificial selection. 

*The selection & breeding of organisms for desired traits is called artificial selection. 

Many domestic plants & animals are produced from artificial selection. These pigeons look different from their ancestors. Darwin realized that changes caused by artificial selection were much like changes caused by natural selection. Instead of nature selecting variations, HUMANS SELECTED THEM. Today, this process is called selective breeding. 

*In both processes, the organisms with desirable traits have better chances of surviving, reproducing, and passing these traits to future generations.