On this year's Earth Day (tomorrow), the Center for Biological Diversity wants you to think about the link between human population growth and wildlife extinction, so they're putting images of some of the planet's endangered species on sustainable condoms.The project, a collaboration between the center and Sustain Condoms , is focusing on polar bears, whooping cranes, monarch butterflies, sea otters, hellbender salamanders and horned lizards."Nothing sparks a conversation like handing someone a condom, especially when it comes with a slogan like, 'Before it gets hotter, remember the sea otter,'" said a statement by Stephanie Feldstein, the center's population and sustainability director. "On Earth Day, everyone is looking for how they can save the planet. Talking about population and overconsumption, and understanding how we influence the world around us every day, is one of the most important steps we can all take to help the environment and our communities."Since 1970, the world's population has nearly doubled from 3.7 billion to 7.2 billion, while wildlife has dramatically declined, according to the center.The organization proposes easy access to family planning, contraception and reproductive healthcare, sex education and women empowerment as options that can lead to long-term solutions to the exorbitant population growth.Tomorrow, more than 500 volunteers will be giving away 50,000 free Endangered Species Condoms at Earth Day events on college campuses and various venues around the country.(If you get one, take a photo and show us before you use it!)Also, you can get more information on volunteering tomorrow or getting some of these condoms on the site, endangeredspeciescondoms.com