Evolution is a painfully slow process, only noticeable under close examination. Charles Darwin was slightly more interested in fossils than bands, but The Thermals’ gradual transformation is moving at an equivalently glacial pace. Each of the Portland trio’s five albums has presented tiny mutations of their poppy punk sound. They’re almost inaudible from one record to the next, but compare Personal Life to debut More Parts Per Million and it’s difficult to believe it’s the same band.

More Parts Per Million is scratchy, succinct, exuberant. Personal Life is defiantly calm by comparison. In between the two is the breathless Fuckin’ A, the raging The Body, The Blood, The Machine and last year’s Now We Can See, comfortably their most polished collection to date. Personal Life takes that mood as its starting point and stretches it out until it’s close to breaking.

Deliberate chords are left to breathe here for twice as long as they would have two albums ago and there’s a sense of space to the music which is an entirely new feeling for a Thermals album. Some parts are almost epic, like the gently reverbed (gulp) Kings Of Leon-style guitar that colours ‘Never Listen To Me’. The kick drum and snare sound like they’ve had a crisp packet taped onto them and a hidden fiddle nags for attention in the thrilling build up of the song’s intro. Tiny touches, but effective at bringing atmosphere to what's a typically straightforward Thermals song at its core.

There’s still something approachably simple about this record. ‘I Don’t Believe You’ packs an irresistible “oh-oh-oh / oh-oh-oh-oh!” refrain to go with its vim-filled harmonies and the incredulously spat out title. It’s like a lost blueprint for how Green Day might have grown old gracefully. As ever, Harris’ voice is a mix of ache and orders and he’s allowing himself a little more expression with his guitar, throwing in a minor solo on the sparse ‘Only For You’ and concluding ‘A Reflection’ with 30 seconds of reasonably interesting feedback.

Moments like these are a relief in an album which doesn’t lack for ideas, but will struggle to hold your attention. Sequencing gets tricky when there are so many songs of similar mood at similar tempos. The Thermals will never be a boring band to listen to, but the surely deliberate decision to fill the middle of the record with so many mid-paced songs is going to test some long-term fans. Rather than the bold riffs and brash hooks of old, most of Personal Life’s songs have single-string guitar lines as their key instrumental motif and they're just not interesting enough to carry the load. 'Not Like Any Other Feeling', 'Power Lies' and 'Alone A Fool' are especially monotonous and lack for anything memorable. Coming as they do as fourth, fifth and seventh songs on a ten song record, they deliver a near-fatal lull way too early.

Harris’ lyrics are also changing, with no instructions to “pray for assassination” here, as on Fuckin A’s ‘God And Country’. These words are largely for and about someone in a couple. There's an eloquently straightforward statement about the power of relationships in the album bookends ‘I'm Gonna Change Your Life’ and ‘You Changed My Life’. When Harris sings the latter so directly, unadorned by the protection of metaphor, it’s tremendously touching – the ultimate compliment you could give someone.

At this point in their evolutionary process The Thermals’ songs can’t match the grandeur of such statements. Hutch isn’t rabble rousing anymore, but his singing is still declamatory and clipped which makes it sound like he's just shouting all these emotive lyrics into his beloved’s ear. It’s a funny image, but it’s not nearly as fun as railing against the president, the church, or the culture as they have done before. The Thermals are in transition, sitting awkwardly between their lo-fi roots and a clear desire to do something grander. They seem stuck at a point where their skeleton is no longer fit for purpose.