Video Transcript
Which of the following best defines
the term “species”? (A) A group of organisms that
belong to the same kingdom and have a similar cellular structure. (B) A group of organisms that share
some similar structural and behavioral characteristics. (C) A group of living organisms
that share similar characteristics and are capable of breeding to produce fertile
offspring. Or (D) a group of organisms that
live in the same place and have similar food habits.
To help us answer this question
correctly, let’s first review some key facts about the classification of
organisms.
There is such an amazing and
diverse variety of organisms on Earth that it can be quite difficult to know where
to start when trying to study it. This is where taxonomy comes
in. Taxonomy is the science of
organizing living and extinct organisms into groups that have similar features. The organisms are placed into
hierarchical groups, which means the organisms are placed into large groups to start
with, based on a few similar features. And then these groups are split
into smaller and smaller ones until they very closely resemble each other. This splitting of organisms into
taxonomic groups based on their observed similarities is called classification. It enables scientists to study
organisms and to be able to discuss findings with others all over the world.
Looking at us, as an example,
should help our understanding of how this works. We are part of the large animal
kingdom. Animals are multicellular, in other
words, made up of many cells. Their cells have a nucleus and no
cell wall, they can move from place to place, and they have to eat their food.
Animals can then be split down into
two groups: the vertebrates and invertebrates. Vertebrates have a backbone, and
invertebrates, as you may have guessed, do not. The vertebrates can then be split
down into fish, reptiles, birds, amphibians, and mammals. All the organisms in each of these
groups have similar features. You can see here that all fish have
gills. All amphibians have smooth, moist
skin. All reptiles are covered in dry
scales. All birds have wings. And all mammals have hair or fur
and feed their young on milk produced by the mother.
We are animals, but we do not share
many similar features to an ant, another animal. We are vertebrates but do not share
many similar features to a snake, which is also a vertebrate. But when you look at the mammals,
we start to share more features with other mammals, such as horses, pandas, and
dogs. Once you get to the small group
known as “species,” all the organisms share very similar features. All humans, Homo sapiens,
are the same species and share extremely similar features. We only vary in small ways, such as
height, eye color, and skin color.
Any organisms of the same species
have similar characteristics, and, very importantly, they can breed together to
produce fertile offspring. When we say an organism is fertile,
it means they can have offspring. Some organisms share similar
features and can breed together to produce offspring, but their offspring are not
fertile. This is because although they share
similar features, they are not actually the same species. Examples of these are tigers and
lions that produce ligers. Ligers are not fertile and so
cannot have offspring themselves. Another, more common, example is a
horse and donkey, which produce a mule. Again, mules are infertile so
cannot breed to produce their own offspring.
Now that we have reviewed some key
facts about taxonomy, classification, and species, we can return to our
question. We now know that the correct answer
is option (C). The statement that best defines the
term species is “A group of living organisms that share similar characteristics and
are capable of breeding to produce fertile offspring.”
