The Singer: We featured the peerless Marvin Gaye a few weeks ago with his uber-slow jam "Let's Get It On." There's not much more to say about him that you don't already know: he's as good of an artist as this country has produced. And in honor of Earth Day, we again highlight Gaye and his call to global awareness.

The Song: One of the first and most enduring songs about eco-consciousness in pop music history, "Mercy Mercy Me" takes a personal, emotional appeal in discussing environmental disasters. The song was one of the big singles from Gaye's game-changing What's Going On, along with the title track and "Inner City Blues (Make Me Wanna Holler)."

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The Singers: Along with the Stylistics, the Spinners and Harold Melvin & the Bluenotes, the Delfonics were one of the premier Philly soul acts of the '60s and '70s. Hit-making producer Thom Bell helped the group hone its sound with hits like "Didn't I (Blow Your Mind This Time)" and "La-La (Means I Love You)." Bell wrote and produced this week's jam, "Ready Or Not Here I Come (Can't Hide From Love)" -- the man clearly loved parenthetical phrases in his song titles.

The Song: The turgid strings and bowel-shaking low brass that introduce "Ready or Not Here I Come" hint at the obsessive streak that runs through this brief tune. Think of it as a precursor to great stalker love-songs like the Police's "Every Breath You Take" and Elvis Costello's "Alison." The song also features founding member Randy Cain, who died last week at the age of 63.

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The Singers: Founded by brothers Robert and Ronald "Kool" Bell, Kool & the Gang was one of the most successful funk acts of the '70s and '80s. Best remembered for dance-club hits like "Jungle Boogie" and "Ladies' Night," the group also had a slower side. Singles like "Cherish" and today's jam "Joanna" showed a softer, more sensitive side.The Song: With a vocal harmony part reminiscent of doo-wop, "Joanna" floats along like a glossy soap bubble. Singer James "J.T" Taylor (not to be confused with the Handy Man) has a voice to match the effervescent production, and that smooth trombone solo is icing on the cake.

The Video: Talk about taking liberties with a song's lyrics: who knew that Kool & the Gang were singing about a waitress at a greasy spoon? According to the video, Joanna is a middle-aged coffee-slinger who used to be a Cotton Club startlet in her youth. So perhaps when Taylor sings that "she never lets me down, especially at night," he's speaking to Joanna's skills with eggs and hash browns, not her amorous charms.

The Singer: We're covered Marvin Gaye in this space before (with "Sexual Healing"), but we're giving him another airing for this sad and special day: Today marks the 25th anniversary of Marvin Gaye's shooting at the hands of his father (he died the next day). I'm not much for numerology, but it's fitting that as Motown celebrates its 50th anniversary this year, we mark the 25 years since the loss of one of the label's true artists.

The Song: "Let's Get It On" was hardly the first song to be considered a Slow Jam, but it may stand as the finest model of the genre. Every piece of the song just falls into place, from the weepy, wah-wah guitar intro to the attack-and-release drumbeat to Marvin's gentle but unwavering commitment to gettin' some. And while I haven't done the research to back up this claim, I've always suspected that Marvin's use of colloquial language his songs (from "I'll Be Doggone" to "I Heard it Through the Grapevine") has impacted the proliferation of these terms in American slang. "Let's Get It On" -- as a song and as a come-on -- stands as a testament to his powers of language and songwriting. Oh, and it will totally help you get laid.

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The Singer: Bill Withers is an odd success story in the annals of soul music. His singing style is affecting but often understated, the instrumentation in his songs was often minimal, and his persona was so low-key that he often seemed to fade into the background of his own songs. His hits -- "Lean on Me," "Just the Two of Us," "Lovely Day" -- still stand as upbeat, uplifting soul songs, but he got funky and a little raw with 1972's "Use Me."

The Song: Slow jams often feature duplicitous paramours and faithless lovers, but few songs sing the praises of a shady lady like "Use Me." Built around a prickly clavinet bassline and rimshot-heavy drumming, "Use Me" lays a simple groove for Withers' tale of barely-coded carnal delight.

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The Singers: Heatwave was helmed by brothers Keith Wilder and Johnnie Wilder, Jr., but the band's secret weapon was organist and songwriter Rod Temperton. The Englishman wrote all the songs on Heatwave's debut LP, including today's slow jam, but Temperton racked up a massive amount of songwriting credits after leaving Heatwave. According to his Wikipedia entry, he wrote or co-wrote songs such as Michael Jackson's "Thriller," Michael McDonald and James Ingram's "Ya Mo Be There" and George Benson's "Give Me the Night."  More >>

The Singer: Stax recording artist, Shaft theme singer, King of New York, voice of South Park's Chef and Scientologist: Isaac Hayes amassed quite the rap sheet before his death last year. He started as a songwriter for Stax Records and became a singer in his own right in the late '60s. Today's cut comes from 1969's Hot Buttered Soul, though the album's 12-minute version of "Walk on By" is truncated here. More >>

The Singer: Born Helen Folasade Adu in Nigeria, the singer known as Sade found her way to music a few years after arriving in London to pursue a career in fashion. In 1982 Sade formed the band that shared her name (a trait that makes her something of a precursor to PJ Harvey). Her debut, 1984's Diamond Life, contained "Smooth Operator" (her best-known song), but this week's slow jam comes from her sophomore effort, Promise.More >>

The Singers: Though born in Chicago, Donny Hathaway was raised in St. Louis: He grew up in a housing project in the Carr Square neighborhood and attending Vashon High School. Hathaway began singing gospel at a young age but made his mark in the soul scene back in Chicago. His most enduring composition is the holiday hit "This Christmas," though his 1972 collaboration with Roberta Flack (of "Killing Me Softly" fame) earned the duo a Grammy for this week's slow jam, "Where is the Love." Despite his cool exterior, Hathaway suffered from depression and paranoid shizophrenia, and he committed suicide in 1979. Hathaway is buried in the Lake Charles Cemetery in North City's Bel-Nor neighborhood.  More >>

The Singer: Hailing from Atlanta, Gladys Knight fronted her brother and two cousins in the Pips from 1953 to the late '80s, though the best-known incarnation of the Pips recorded between 1967 and 1975. The quartet recorded for Motown in the '60s but found greater fame on the Buddha label, which released "Midnight Train to Georgia" in 1973.

The Song: "Midnight Train" is a little more gritty and Stax-y than most slow jams we've featured here, but the soul and sentiment comes through. When Gladys sings "I'd rather live in his world than be without him in mine," it basically condenses every love song down to one line. More notable, though, is the back-up vocals by the Pips: rather than simply echo the lead singer's lines in harmony (like most back-up groups did), the all-male Pips provide a Greek Chorus for Gladys. It's an elegant solution to a tricky gender issue.

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