One step, another, and a hop outward.


Somersault once, kick back, arms up, and knife cleanly through the surface of the water like a sword through cake. Clean. Not a drop out of place in that dive, hardly a splash. So why did you do it? Says Bonnie Tsui in "Why We Swim," there could be many reasons.


If there's one thing you know about summertime, it's that it can get hot. Like, melt-your-shoes hot, crispy-grass hot, sweat-til-you're-wet hot. And that's when any size pool of water starts to look mighty tempting. But, says Tsui, "We ... are not natural-born swimmers ..." Throw us in the water and, without lessons, we flail.


Lessons aside, though, cave art discovered in 1933 shows that humans have been swimming for at least 10,000 years and they probably learned how by watching those who figured it out even before them. That likely happened in the Green Sahara, where there were once verdant meadows and cool pools.


Bottom line: We are land animals that are attracted to water, and not just to drink. Scientists call us secondary swimmers although, in some cultures, it seems as though our fellow humans are half-fish. Hailing from southeast Asia, the Moken people can see underwater in ways that most of us can't; many Bajau from the same area are born with spleens that allow them to stay underwater for minutes, rather than the pathetic seconds most of us can manage. Japanese ama are able to deep-dive hundreds of times a day. Yes, even some Americans can swim with an endurance that may sound superhuman.


But it's not, not really. For some people, it's a matter of genetics and having been blessed with a physical quirk that allows impressive feats in the water. For others, it's a challenge, a lifesaver, an obsession, a hobby, or pain to overcome. And for some, says Tsui, it's a matter of ensuring that "we ... teach ourselves how to live with water, not how to keep it at bay."


So, you say you're landlocked. Not much more than a puddle in sight. And that's okay: Instead, dive into "Why We Swim" for some cool refreshment.


Indeed, author Bonnie Tsui's writing brings such strong images to mind — of water, of cold or heat, of the kicks and reaches that swimming requires — that you'll almost hear the seagulls and you'll want to reach for a towel. This will remind you of swim meets in high school, of skinny-dipping in the lake, and building sand castles on the shore.


But it isn't just the sense of beachiness that's inside this book: Tsui also offers readers history and science, psychology, and several interesting mini-bios of people who've astounded researches, both accidentally and on purpose, with their prowess in the water. She also includes personal stories as a sort of glue to hold this book together.


If you're heading for the water today, or staycationing by the pool, you'll need something to read, right? So take "Why We Swim." For you, it'll make a nice splash.