What is a Species? - Definition & Explanation

What is a Species? - Definition & Explanation
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  • 0:01 Biology and Classification
  • 1:58 What Is a Species?
  • 3:45 Reproduction and Types…
  • 5:06 Lesson Summary
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Lesson Transcript
Instructor: Adrienne Brundage
In biology, a species is one of the basic units of biological classification. It most commonly refers to a group of physically similar organisms that can exchange genetic information and produce fertile offspring. Learn more in this lesson.

Biology and Classification

Imagine you're out with friends and joking about that new guy at work. 'It's like he's a different species!' you say. But what does that actually mean? What is a species? How do scientists tell the difference between all these different species on Earth? Well, this is a topic of active debate among biologists, but we have all agreed upon one thing: the idea of a species is fundamental to the study of biology.

Biology is concerned with studying the life around us, and to make that easier, biologists like to group things together. These groups tend to consist of organisms (living things) that look or act alike. This allows us to study different plants, animals, and microbes based on what they have in common with each other. Did you ever play that game 20 Questions, and the first question asked is: 'Animal, vegetable, or mineral?' The answer to that question helped in the game, and it helps in science. Looking at living things in groups makes it easier to discover how different organisms work.

To efficiently put organisms in different groups, scientists developed a system of classifying these organisms. This system takes all the organisms on Earth and puts them in groups based on body form, genetic similarity, body chemistry, development, and behavior.

The study of organisms in this way is called systematics. Systematics starts with very large groups, based on very broad criteria, called domains. There are only three domains, and all life as we know it fits into one of these three groups. The groups get smaller and more specific, and the organisms in each group get more and more alike until we reach the smallest group, the species. Scientists estimate there are 30 million species of living organisms on Earth.

What Is a Species?

But how do we recognize a species?

This is a harder question to answer than you think. The most common definition of a species is: a group of organisms capable of interbreeding and producing fertile offspring. This definition works well, for the most part.

Let's look at an example. You buy a new, beautiful purebred show poodle and plan to take her on the dog show circuit. How fun! One evening, the neighbor's golden retriever-lab mix gets into the yard, and a few months later, you have an adorable basket of poodle-golden retriever-lab puppies up for adoption. Those puppies grow up and have puppies of their own. What do we know about the poodle and golden retriever from this experiment? We know they are the same species. Even though you may have spent thousands of dollars on a purebred show dog, that dog is still able to mate and produce fertile offspring with the neighbor's mutt. According to the biological species concept, this means they are in the same species group.

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