Darwin's Four Postulates
The Key to Evolution
An example of this can be seen with the harlequin ladybirds shown in the picture below.
An example of this postulate is parents passing on their eye colour to their children.
An example of this is a tiger being hunted or poached by humans. Despite the tigers being the biggest member of their own food chain they can still die to external factors.
An example of this is the giraffe who has very long necks to reach the fruit in the trees. They evolved this long neck because they could not obtain food otherwise.