BRITAIN’S favourite TV scientist is back – this time exploring the origins of man instead of the universe.
Professor Brian Cox delves into evolution in new BBC series Wonders Of Life, starting on BBC 2 on January 27. Here, the Sun Professor, writing exclusively in Day One of a series, explains how the aye-aye of Madagascar helped him to understand how life began.
ASK a biologist how many species live on Earth today and the chances are you will get a shake of the head — because we simply do not know.
A recent estimate put the number at 8.7million, but others range from 3million to 100million.
What is known is that 1.3million species have been catalogued, of which we are one.
And every single species on Earth today — no matter how many that is — has a great deal in common.
The basic chemical reactions that power all life are the same.
If you trace your genetic line back through the centuries, you will arrive at a small group of ancestors living in the vicinity of the Great Rift Valley around modern day Ethiopia and Kenya around 2million years ago.
Go further back through millions more years and you will find shrew-like mammals, amphibians, fish, the first vertebrates, the first complex cells, and so on — all your ancestors.
There is an unbroken line, stretching back 3.8billion years or more, from you to an original population of living things — the foundation of all life on Earth today.
Meeting the family ... Brian Cox and aye-aye
They are collectively known as LUCA — the Last Universal Common Ancestor.
We don’t know what LUCA looked like, but one of the most widely accepted theories is that our common ancestor wasn’t a cell or even some kind of free-living thing at all.
It was a set of chemical reactions occurring inside rocky chambers around volcanically heated hot springs, deep below the primordial oceans of Earth 4billion years ago.
And we all STILL carry the chemistry of the primordial Earth.
While the origin of life is a matter for scientific debate, the explanation for the emergence of today’s endlessly complex tree of life is not. Just over 150 years ago, Charles Darwin got it broadly right.
A beautiful example of Darwin’s great idea is found on Madagascar, off the eastern coast of southern Africa.
Around 65million years ago, a handful of seafarers were nearing the end of a 350-mile voyage on a natural raft of vegetation.
They were accidental travellers — creatures from mainland Africa that had been trapped and taken by the ocean’s currents.
The land they found was rich in trees, plants and animals, but there were none of their kind.
Fate brought a group of animals known as lemuriformes to the island and, over time, those ancestral primates have evolved and diversified to become Madagascar’s most iconic animals — the lemurs.
Today there are 99 species and subspecies of lemur, none of which are found anywhere else on the planet.
They form a quite dazzling array, and the settlers from the raft are directly related to all of them.
The story of Madagascar’s lemurs provides an excellent analogy with the evolution of life from LUCA to the present day. How did the DNA database of those on the raft expand and fragment to produce the diverse and highly specialised range of lemurs living in Madagascar today?
Jungle book ... Brian Cox's Wonders of Life
The answer can be found by studying one of the most bizarre animals on the planet — the aye-aye.
It is a creature with an almost demonic appearance that lives in a niche occupied by woodpeckers in many other parts of the world.
There are no woodpeckers in Madagascar, which would have meant that — before the aye-aye arrived on the scene — grubs buried inside trees could have led a charmed life immune from predation. The aye-aye is the primate version of a woodpecker, deploying an utterly strange suite of adaptations to exploit the benefits of a wood-boring lifestyle.
The most startling is its unique middle finger, a grotesquely elongated, slender and bony structure with 360° movement on a ball-and-socket-like joint system. It feels broken as you gently rotate it.
The aye-aye’s finger was longer than mine when fully extended, and this on an animal no bigger than a small dog.
The aye-aye uses its finger to tap down the trunk of a tree, listening for a change in sound that may mark the presence of a bug inside. When a promising echo is located by its large, gremlinesque ears, it begins to gnaw through the wood.
Once through the wood, the aye-aye deploys its finger again, spearing the grub inside the hole and levering it out to eat.
This aye-aye’s particular lifestyle explains its unique and startling form.
It is nocturnal, so it has large eyes. It is a tree-dweller, which explains its dexterous hands, feet and large, counter-balancing tail.
Its odd, rodent-like teeth allow it to gnaw through wood and that strange central finger allows it to access a readily available food source, safe from the competition of other large animals and birds.
We can now draw all the threads together to describe how the aye-aye came to be the way it is.
At some point around 40million years ago, a random change in the DNA of a lemuriforme would have resulted in a very slightly elongated middle finger.
This was almost certainly an unnoticeable change, and may have conferred little if any advantage at all at first.
But the possessor of the mutation certainly survived long enough to pass it on to its offspring.
Given time, this lengthened middle finger must have allowed a group of these ancestral aye-ayes to begin to exploit a new niche.
Perhaps they could spend slightly more time high in the canopy, as they could get to easily accessible bugs in cracks in the wood.
'Even me? Why-aye pet' ... Cheryl Cole
So, this particular group of animals, carrying this lengthened middle finger mutation, began to separate from that of the other lemurs, who spent less time on tree trunks foraging for bugs.
Eventually, as further mutations in the DNA of this now-isolated group occurred, they were tested by the sieve of natural selection.
So the ancestors of the aye-ayes become so different from the other lemurs that they are today clearly identifiable as a completely separate species.
This is Darwin’s explanation for the origin of species, “the endless forms most beautiful” as he put it, that we find on Earth today. Over 3.8billion years, random changes in DNA, tested by the non-random sieve of natural selection, has produced the magnificent diversity of life on Earth.
Darwin wrote: “There is grandeur in this view of life.”
And understanding how our unique and complex living world emerged from a collapsing cloud of gas and dust almost 5billion years ago surely only adds to the wonder.
Wonder land ... the Great Rift Valley in East Africa
The accompanying book to Wonders Of Life, written by Brian Cox and Andrew Cohen, will be published next Thursday and costs £25.
