Rhys Green of the Royal Society for the Protection of Birds in Edinburgh
looked at eggs from the four species of thrushes with more than 1000 breeding
pairs in Britain: the blackbird, song thrush, mistle thrush and ring ouzel,
which breeds mostly on moorland. He visited the Natural History Museum in Tring,
the Royal Museum of Scotland in Edinburgh and the Liverpool Museum, which have
collections dating from around 1850. “We wanted to see if there were long-term
trends that might be related to environmental pollution,” says Green.

His results, published this week in Proceedings of the Royal Society
B (vol 265, p 679), reveal a steady decline in eggshell thickness totalling
between 2 and 11 per cent, depending on the species
(see Figure). For the
blackbird, eggshells seem to have started to become thicker once more from about
1960. Because the collection sites are well documented, Green is confident that
the changes he has recorded are genuine, rather than artefacts caused by eggs
being taken from different geographical areas at different times.

But what could be to blame? Organochlorine pesticides such as DDT are known
to cause thinner shells in birds of prey. But these chemicals only became widely
used in British agriculture in 1947, well after the thinning of thrush eggshells
began.

Green thinks that acid rain, caused by sulphur emissions from the burning of
fossil fuels, is the most likely cause. This would reduce both the calcium
content of leaf litter consumed by worms and the abundance of snails, which
together make up a large part of the birds’ diets.

Eggs laid by great tits living in areas with heavily acidified soils have
been found to have thinner shells than normal, Green notes. One study in
Germany, published earlier this year in the Journal fĂŒr
Ornithologie (vol 139, p 3), found that eggshells from birds living in
areas where soils are highly acidic were 2.7 per cent thinner than those from
lime-rich areas.

More studies are needed to identify exactly how historical increases in soil
acidity relate to trends in eggshell thickness, says Green. And it is still
unclear whether the changes are affecting the birds’ survival. “Whether these
processes actually affect the conservation welfare of the thrushes is not yet
certain,” says Green.

Green would also like to find out why blackbird eggshells now seem to be
getting thicker again. “It is tempting to relate this to the clean air
legislation of the 1950s,” he says.

It is the outpost on which Britain still relies as a refuelling base for its
forces en route to the Falklands. It is a vital radio communications post, and
is also leased to the US as an airbase. It has served Britain and its allies
well, but now the British government seems unwilling to accept its
responsibilities in return.

How can action—or, more exactly, inaction—on this rather barren
island, blasted by tropical heat, prompt such troubled reflections? The story
began several hundred years ago, when rats and then cats got ashore from ships.
The intruders found an island chock-a-block with all manner of nesting tropical
seabirds, for the island is the only speck of land in a huge tract of ocean.
Cats and rats have since munched through the defenceless birds until most
species were banished to an offshore rock, Boatswain Bird Island—
only sooty terns remain.

To restore Ascension to something closer to its former, bird-thronged glory,
scientists who worked on the island during a British Ornithologists Union
expedition suggested that the cats and rats should be eradicated. For more than
thirty years, this proposal got precisely nowhere. Then, in 1992, Britain signed
the Biodiversity Convention, thereby committing itself to “eradicate
 alien
species which threaten ecosystems, habitats or species”. Responsibility was
publicly acknowledged. A sigh of relief went up from conservationists. And, in
1995, a feasibility study for eradicating cats and rats was undertaken by
Wellington-based Wildlife Management International (WMI), funded jointly by the
Foreign and Commonwealth Office, the Royal Society for the Protection of Birds
and the World Wide Fund for Nature.The resulting report by the New Zealand
experts pronounced that eradicating wild cats and neutering domestic cats was
practical (at a cost of ÂŁ360 000), while rat eradication (at a likely cost
of ÂŁ730 000) should ideally be delayed a few years until researchers had
developed a bait that would be eaten by rats but not by land crabs. The
islanders were not altogether happy with this, fearing that during the period
without cats, the rats would multiply. The scientists doubted that cats there
had any controlling effect on the rats—and in any case, it is a moot point
whether the wishes of temporary settlers, in this case St Helenans working
mainly on contract at the airbase, should determine the fate of wildlife that is
an international heritage.

But back to the drawing board went WMI. The revised report came up with a
joint attack on rats and cats, though the cost had escalated to ÂŁ1.5
million. All parties agreed on the new plan, provided it could be funded. And in
early 1996, the British government earmarked the modest sum of ÂŁ30 000
towards this total.

There was clearly much fundraising to be done. The voluntary bodies, such as
the RSPB and the WWF, had already embarked on this task, when a distressing
series of events unfolded. First, the starter funding from the government was
reallocated. Secondly, the Governor of St Helena, who is responsible for
Ascension, indicated that he would block any application to the European Union
for funding, even though the conservation bodies were not planning to compete
for the same European budget lines as those targeted by development projects on
St Helena. And thirdly, the British government refused to liaise with the US
government, major users of the Ascension airbase, to help the search for North
American funds for the ecological restoration.

Mike Pienkowski of the RSPB and chairman of the UK Dependent Territories
Conservation Forum says “I find it difficult to believe the government intends
to go back on the commitments it made only a few weeks ago in its response to
its steering group on biodiversity. It indicated that it would work in
partnership with voluntary bodies to help conservation action in its Dependent
Territories. We are ready to play our part, but we need the government to play
Ÿ±łÙČő.”

So, the situation is that the government first orders a study, with an
implicit understanding that ways of funding a project will be sought if a
solution is viable. Then, when the WMI emphatically concludes that action is
both feasible and desirable, though expensive, the government blocks all further
progress.

No doubt it does not want to foot the bill. Fair enough, governments hate
footing bills. But to proceed from there to obstruct the nongovernmental
organisations in their efforts to find funding, and to refuse to engage in any
constructive discussions with other governments in the search for a solution, is
a shameful denial of responsibility. The green turtles of Ascension, which have
swum from Brazil to nest on the island’s beaches, must be weeping.

Biologists have traditionally seen sex as a game played out by choosy females
and promiscuous males. According to evolutionary theory, males should try to
mate with any females they encounter if they want to pass their genes on. But
females are not supposed to reproduce so wantonly because they usually get
saddled with raising the offspring. This means that they should aim to choose a
high quality male who will sire similarly fit young.

Recently, however, researchers have begun to realise that in some
species—particularly those that form long-lasting pair bonds—males
may be more discriminating than they have been given credit for, and seek out
females who are likely to produce more offspring.

Because zebra finches are monogamous and readily pair in captivity, they are
an ideal species for the study of male mate choice. And it turns out that male
zebra finches make surprisingly subtle distinctions between prospective mates,
according to Glasgow University researchers Pat Monaghan, Neil Metcalfe and
David Houston, who report their work in the latest issue of Proceedings of
the Royal Society B (vol 263, p 1183).

The researchers separated a captive population of female finches into two
groups of equal size, one fed millet alone, the other fed millet plus a
supplement of protein from hens’ eggs. In previous experiments, Richard Selman,
also at Glasgow, has shown that females fed this supplement produce larger and
more viable clutches of eggs. During the feeding phase of the experiment, which
lasted for two weeks, the females were out of sight of males. Afterwards, pairs
of females, one from each group, were each caged with a single male.

On the day after being caged together, more than two-thirds of the 29 males
in the experiment directed most of their courtship to the female that had been
fed the supplementary protein. The vast majority directed more than 90 per cent
of their attention to the well-fed female.

The females did not differ in body mass, age or any other obvious physical
characteristics, so it is unclear how the males made the discrimination.
“Perhaps the females fed supplementary protein showed subtle postural
differences that the males could detect,” says Metcalfe. “Or perhaps their calls
differed. We are really not sure.”

This set me thinking. If the very best brains in the scientific business really do not have much clue where their own speciality is heading, perhaps this tells us something fundamental about the nature of scientific progress?

Science can be thought of as a river. In the past, the river was young and flowed through a single channel in the hills. A scientist swimming in the river could easily look across to the left and right banks and encompass in one gaze the entire breadth of scientific knowledge.

Now science has matured. The river has reached a well-wooded delta and split into a multitude of channels, separated by islands, meanders and oxbow lakes. The foot soldiers of scientific progress, the PhD students, swim in the river. With their heads just above water (if lucky), they can see the route over the next few yards, but no farther. They may be fortunate and find themselves in the mainstream, but there is a real risk that without guidance they will end up stuck in a channel from which there is no exit.

By the time our postgraduates have secured a postdoctoral position or some permanent job, there is a chance that a few of them will manage to clamber aboard some passing tree trunks. But while these lucky ones have little opportunity to steer their own course, for the current is dominant, they are at least able to see the banks of the channel along which their own trunk drifts. For better or worse, they can assess their contributions within the speciality in which they work. But they still cannot see the “big picture”, the whole river, and they cannot see any useful distance into the future.

The most talented of the bunch not only clamber onto a steadier log, but manage to grab a branch so they can paddle ashore. They probably land on a small island somewhere in mid-delta. After exploring the island, they appreciate better how their channel of scientific progress relates to neighbouring disciplines. Nevertheless, the trees growing on the island prevent any long-distance view. To gain that over-view, it is essential to climb a tree.

Only the very talented can climb trees. But there is a problem. From the ground it is impossible to tell whether the trunk before them goes only as far as the lower canopy or emerges above the forest canopy. If the former, the view is not much different from that on the ground. If, on the other hand, the scientist has, in the first place, the talent to be a tree-climber and, in the second, the good luck to have selected an emergent tree up which to clamber, our scientist is hailed as a genius.

From the treetop vantage point, he or she can discern how the many channels of the scientific river intermingle. They can appreciate the most important channels of the day and spot the most sluggish and unproductive. But there is still an important asymmetry. Because rivers start steep and then flow along a gentler gradient as they near the sea, any view from the delta is always likely to offer better vistas upstream than downstream. Even for the treetop genius it is easier to appreciate, integrate and explain the scientific flow of the past than it is to peer forward across the flat canopy of the delta’s trees and struggle to make out where the flow will be strongest in the future.

It does seem then that the progress of science is analogous to a flowing river. Both are driven forward by a powerful head of pressure – the one by gravity the other by the body of scientists and their collective knowledge. In neither case has any one point in the flow a view of its ultimate destination.

If the most talented scientists have the most coherent appreciation of the forward flow of science, it is important that they are the ones who allocate scarce research funds. But woe betide us if the ultimate arbiter is some second-rater struggling to stay afloat on his or her log. It will be no surprise if the resulting referee’s report is a page of visionless nit-picking.

Finally, just before the river eventually discharges into the sea, there are signs that the myriad channels of scientific progress may be coalescing. Perhaps, then, just as a river becomes so broad that one bank is invisible from the other, the boundaries between science disciplines will one day vanish. Then all knowledge could become contained in one Grand Unified Theory of Everything.

One thing is sure. The decades ahead will be exciting ones for anyone launching onto the river of scientific progress.

Handedness is partly under genetic control. The proportion of left-handers – 13.0 per cent in males, 10.7 per cent in females – is similar in all ethnic groups. This minority status is the key to understanding their survival, according to Michel Raymond of the University of Montpellier. Left-handers need not be inherently superior fighters, he says. But as long as they remain in the minority, they will be at an advantage each time they fight a right-hander.

Right-handers, the argument goes, will face an unfamiliar type of opponent each time they take on a southpaw. The left-handers, however, should be more than used to taking on a right-handed opponent. “Since women fight less than men in the majority of cultures, this could explain why left-handedness is consistently rarer in women than men,” says Raymond.

Testing this idea was tricky, however, as Raymond could not ask people to engage in mortal combat. Instead, he looked at data from sporting contests, working with Anders Moller of Copenhagen University and researchers at the University of Lyon. Raymond described these results earlier this month in Edinburgh, at a meeting of the European Society for Evolutionary Biology. For sports which do not involve face-to-face duels, such as swimming or athletics, Raymond found that the proportion of left-handers among sportsmen and women was no higher than normal. But the picture changed when he looked at sports involving individual confrontation.

In the case of tennis, with the opponent a court’s length away, left-handers were more common than expected. Raymond looked at the world rankings for 1994 and 1982, choosing two widely spaced years to get different players. Although there was no excess of left-handers among the women, 16 per cent of men ranked in the top 100 were left-handed.

The results became more striking for sports which bring adversaries closer together. Thirty per cent of top junior Danish male table tennis players are left-handed, the researchers found. And in the true combat sport of fencing, half the men and one third of the women reaching the quarter-finals of the world championship between 1979 and 1993 were left-handed.

“This is fascinating work,” says Robin Dunbar of the University of Liverpool. “It’s the most sensible idea I’ve heard about this problem for a long time.”

The world’s media, from the Reader’s Digest to the San Francisco Chronicle,
latched onto the story. The message was appealingly simple. If the debris
of humankind, the polluter, had reached Ducie, 5000 kilometres miles from
any large landmass – New Zealand to the west or South America to the east
– where on Earth might a rubbish-free spot be found?

Yet the self-flagellating response was only part of the story. The conservation
problems of the Pitcairn Islands – the two low atolls of Ducie and Oeno,
Pitcairn itself (home to the 60-odd descendants of the mutineers from the
Bounty), and the uninhabited World Heritage Site of Henderson Island – can
be traced back hundreds of years. The problems started, in fact, with the
Polynesians who arrived at the islands around AD 800. That is the bad news.

On Henderson, the expedition found that Polynesian rats, Rattus exulans,
which the Polynesians had deliberately released onto the island to provide
protein snacks, were killing the great majority of gadfly petrel hatchlings.
These ocean-going seabirds were able to hatch their eggs without undue
difficulty. But once the downy chick moved from under the parent’s sheltering
body, it was snatched by rats.

This might not be too urgent a conservation issue if all species of
petrel were widespread. But for one species, Henderson Island is probably
the world headquarters. If the island’s population of petrels is lost to
rat predation, the species might disappear forever. The problem is that
Henderson, at 37 square kilometres, is some ten times larger than the largest
island from which rats have been successfully eliminated. Rat control is
perhaps not feasible on Henderson, but it would be practical on Oeno, whose
mere 65 hectares of land sit in the bluest of lagoons. Cleared of rats,
Oeno could provide a safe haven for the petrels.

Henderson Island is visited about once a year by the Pitcairn Islanders,
who cut two hardwoods there that they call tao and miro. These woods, taken
from trees that were themselves brought to the island by Polynesians, are
then crafted into fine carvings which generate important income for the
islanders. However, since the advent of chainsaws, the islanders have been
harvesting the hardwoods more vigorously than is sustainable. Yet they naturally
want to maintain the woodland. So too do conservationists since, ironically,
the Henderson woodland represents a type now rare elsewhere in Polynesia.
Management is clearly required. Such management needs expert forestry advice
and a new boat to allow the Pitcairn Islanders to travel safely to the island
about three times a year.

Forestry management and a new boat were included in the recommendations
of the management plan that the expedition drafted for the Joint Nature
Conservation Committee (JNCC), which coordinates Britain’s national effort
in nature conservation. Yet in the two years since the draft was received,
there has been little obvious progress towards it being adopted. The combination
of the JNCC, the Foreign and Commonwealth Office, the British High Commission
in New Zealand, and the Department of the Environment, which is responsible
for Britain’s World Heritage Sites, has so far proved an administrative
swamp from which the Henderson management plan has yet to emerge. Until
the plan is adopted, there is little prospect of action on the ground.

And what of the blindingly beautiful atolls of Oeno and Ducie? They
are rare examples of atolls in southeast Polynesia that have their original
vegetation largely intact; they are not monotonous coconut plantations.
Oeno holds an important population of the bristle-thighed curlew (Numenius
tahitiensis), a bird with a status bordering on the endangered that migrates
from its Alaskan breeding grounds to the islands of the South Pacific. The
atolls are certainly strong candidates for designation, under the 1971 Ramsar
Convention, which aims to protect wetland sites as one of its objectives.
To its credit, the Department of the Environment did fund a desk-study in
1992 that assessed which wetland sites in the Dependent Territories merited
designation. But since then, nothing.

The conservation problems of the Pitcairn Islands are soluble. Yet it
is difficult to avoid the impression that the government is nervous of committing
itself to spending money, even though the sums would be paltry. A few hundred
thousand pounds, equivalent to a few yards of widened M25, would do the
trick of eliminating Oeno’s rats and restoring Henderson’s woodland.

Mindful of local susceptibilities in the Dependent Territories, the
British government does not wish to appear to be usurping the role of locally
elected authorities. That approach may be high-minded and appropriate for
the 6 million people of Hong Kong. It is clearly inappropriate for the 60
Pitcairn Islanders. For sure, the Pitcairn Island Council should be thoroughly
involved in conservation planning for the future. But it is wholly unrealistic
to expect a council with a budget that might appear meagre to a parish council
to take the lead in conservation matters.

The good news is that the conservation problems of the Pitcairn Islands
– and indeed of most of Britain’s other Dependent Territories – can be
solved if the British government picks up the challenge. By doing so it
could immeasurably enhance its conservation credibility. To use a sporting
metaphor of the type favoured by John Major, it would then have earned its
green cap.

Michael Brooke writes from the Department of Zoology at the University
of Cambridge.

On closer inspection, these apparently altruistic bee-eaters usually
turn out to be males that are helping out either their brothers or parents.
In this way, the bereaved bird is helping to raise young related to itself,
and so ensure the survival of at least some of its own genes.

Being in a position to help one’s relatives would seem to depend on
related birds nesting reasonably near to each other, as the behaviour would
be impractical if birds dispersed so widely between birth and breeding that
colonies rarely contained relatives. Females do disperse widely, and that
is probably part of the reason why they are only rarely helpers. But more
details were needed for a true portrait of how male bee-eaters turn nursemaid.

In a study of the bee-eaters nesting along 2 kilometres of a canal in
the marshy Camargue in southern France, Kate Lessells of the University
of Sheffield, together with Mark Avery and John Krebs of the University
of Oxford, has asked a series of more subtle questions about the phenomenon
(Behavioural Ecology, vol 5, p 105). In particular, the biologists looked
at the dispersal of brothers between one year and the next. They found that
brothers that survive to breed in the following year do tend to nest closer
together than expected by chance. In the most remarkable case, two brothers
dispersed almost 2 kilometres from the nest of their birth, and ended nesting
only 1 metre apart.

Lessells and her colleagues found that the median distance between the
nests of failed breeding males and the nests of relatives was 46 metres
where the male helped and 178 metres where they did not. In other words,
failed breeders were more likely to help, and so enhance the survival of
their nephews and nieces, if they had nested close to a potential recipient
of that help.

These results led the researchers to ponder why, if helping was more
likely when the birds nested near each other, the brothers did not regularly
nest cheek-by-jowl. It turned out that nest failures, which are mostly due
to snakes, tended to occur in clumps. If all brothers nested very close
together, they would tend to succeed or fail together, and helping behaviour
would be irrelevant. Either the birds would be busy raising their own
chicks, or there would be no chicks to raise.

But this poses an awkward question. Does x ‘units’ of molecular difference
between the two lineages always imply a shared ancestor y years ago? In
other words, does the molecular clock tick at the same rate in, say, whales
and mice? The answer is, no. But as long as the molecular clock ticks at
a constant rate in different animal lineages this information can still
be of use. Andrew Martin and Stephen Palumbi of the University of Hawaii
have found that the molecular clock might be better calibrated if these
different ticking rates are taken into account (Proceedings of the National
Academy of Sciences, vol 90, p 4087).

Martin and Palumbi examined data from the globin molecule, which is
coded for by nuclear DNA. They found that in small primates such as spider
monkeys, weighing about 6 kilograms, mutations – substitutions of DNA bases
– occurred about twice as rapidly as in humans, who weigh on average 70
kilograms. This inverse relationship between mutation rate and body size
also applied to the cytochrome b gene, part of the genome of the energy-processing
mito-chondria. Base changes occurred much faster in mice than in much larger
whales.

No one knows why different parts of the mitochondrial genome mutate
at different rates. But because they do, it is better to assess the overall
rate of mtDNA evolution by focusing on the whole genome rather than on a
particular area such as the cytochrome b region. Martin and Palumbi did
this, using a technique known as restriction fragment length polymorphism
analysis. Again, they found an inverse relationship between the mutation
rate and body size.

Polar bears and European brown bears, which shared a common ancestor
about half a million years ago, now show a 1 per cent divergence in mtDNA
sequence. This is equivalent to a 2 per cent divergence per million years.
Human and chimpanzee lineages probably split about 5 million years ago and
now show a 10 per cent mtDNA difference. This too is equivalent to 2 per
cent divergence per million years. At the alternate extremes, the mtDNA
of small rodents diverges rather briskly, at around 5 per cent per million
years, while that of whale species – such as the fin and humpback – has
diverged at a mere half per cent per million years.

Smaller body size tends to mean a shorter lifespan and a shorter generation
time. If each generation represents a new opportunity for DNA substitutions,
then generation time might explain the relation between body size and the
rate of the molecular clock. But generation time is not the whole story.
The generation time of whales is shorter than humans and chimpanzees, yet
whales have a slower substitution rate.

Martin and Palumbi found a clue to the solution when they collated substitution
rates in various ‘cold-blooded’ or poikilo-thermic animals. As before, they
found that rates were slower in large animals such as sharks than in smaller
animals such as newts. But, weight for weight, the poikilothermic animals
had slower rates than the homeothermic birds and mammals. Metabolic rate
therefore appears to be another crucial influence on the rate of DNA substitution.
Whales may not have especially long generation times but they do have a
slow metabolic rate, which would explain their sluggish rate of molecular
evolution.

If DNA damage is related to metabolic rate, the effect may be due to
oxygen radicals, highly reactive molecules which can damage DNA. About 90
per cent of a cell’s oxygen is used in the mitochondria, so oxidative damage
is likely to be greatest there. This may partly explain why the rate of
nucleotide substitution is generally higher in mtDNA than in nuclear DNA.