Although the chemistry of autumn colours is well understood, there is an ongoing and lively debate among scientists about why trees evolved their vivid autumn colours in the first place.

Driving north through Duchess County, New York, in mid-October, I'm flanked by the resplendent golden yellows and fiery red leaves. The pops of colour break open like fireworks when the sunlight dapples across the leaves. It's a harbinger that colder months lie ahead.

Further north in Maine, the colours are far more muted. "In a fall like this one, we have some plants that are [changing] really early and undergoing senescence really quickly because they're drought-stressed," says Amanda Gallinat, an ecologist who studies changes in seasonal events in the natural world at Colby College in Waterville, Maine. When she looks out of her window, she sees a lot of leaves turning brown already.

On the other side of the Atlantic Ocean, similar colour changes occur every autumn in the UK. Here, however, there are far more yellows than reds, due to the dominant species of native deciduous trees – beech, sycamore and oak. "In the UK, the most colourful ones are usually introduced species," says David Wilkinson, an evolutionary ecologist at the University of Lincoln in the UK. Sumach, for example, produces a vivid red, but species of these small trees are native to the Mediterranean, parts of Asia and North America.

Meanwhile, in Japan, the fiery red, purple and yellow shades of the maple transform the landscape and draw tourists by their many thousands. In many parts of the world, "leaf peeping" has become a popular attraction as millions travel to see and photograph the spectacular seasonal shifts in leaf colour. (Find out where to see the best autumn leaf colours in this article by Lynn Brown from BBC Travel.)

Yet, despite receiving so much attention, we still don't really know why trees undergo this transformation in the first place.

While biologists have a clear understanding of the biochemistry that causes the green to drain out of leaves with the change of the seasons to leave such vivid colours left behind, what led deciduous trees to evolve their autumn colours is still a mystery.

A lively academic debate has, in fact, been raging about this very issue for decades. Read on to find out about some of the leading theories.

First, however, it's important to understand what is going on in leaves when they change colour.

Leaves that turn yellow were actually always yellow – the colour comes from a set of biochemical pigments known as carotenoids. These are simply revealed once the green chlorophyll in the leaves breaks down and the nutrients are reabsorbed by the plants as they prepare to hunker down for the harsh winter weather.

Leaves that turn red or purple undergo a slightly different process: their colour stems from a combination of chlorophyll loss and the production of anthocyanins, which are commonly found in many fruits and vegetables too.

In evolutionary biology, however, the fact that these annual changes have persisted in tree species around the world against the ravages of time and natural selection suggests that it may confer some benefit to the trees. Indeed, genetic research has suggested that trees only began producing the pigments responsible for the autumn colours comparatively late in their evolution – long after they began reabsorbing their chlorophyll.

Complicating all of this is that some species of trees will produce multiple different autumn leaf colours, and sometimes

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