Charles Darwin was a careful scientist. In the middle of the 19th century, while he was collecting evidence for his theory that species evolve by natural selection, he noticed it didn’t explain the fancy tails of male peacocks, the antlers paraded by male deer, or why some the males of some species are far larger then their female counterparts.
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For these quirks, Darwin proposed a secondary theory: the sexual selection of traits that increase an animal’s chance of securing a mate and reproducing. He carefully distinguished between weapons such as horns, spurs, fangs and sheer size that are used to subdue competing rivals, and ornaments that are aimed at charming the opposite sex.
Darwin thought that sexually selected traits could be explained by uneven sex ratios — when there are more males than females in a population, or vice versa. He reasoned that a male with fewer available females would have to work harder to secure one of them as a mate, and that this competition would drive sexual selection.
In a new study, it is confirmed that there is a link between sexual selection and sex ratios, as Darwin suspected. But surprisingly, the findings suggest Darwin got things the wrong way round. It is found that sexual selection is most pronounced not when potential mates are scarce, but when they’re abundant — and this means looking again at the selection pressures at play in animal populations that feature uneven sex ratios.
Since Darwin’s time, we’ve learned a lot about uneven sex ratios, which are common in wild animal populations. For instance, in many butterflies and mammals, including humans, the number of adult females exceeds the number of adult males.
This skew is most extreme among marsupials. In Australian antechinus, for instance, all males abruptly die after the mating season, so there are times when no adult males are alive and the entire adult population is made up of pregnant females.
In contrast, many birds parade more males than females in their populations. In some plovers, for example, the males outnumber females by six to one.
So why do many birds species have more males, while mammals often have more females? The short answer is that we don’t know. But there are smoking guns.
Explaining uneven sex ratios
Some uneven sex ratios can be partially explained by lifespan differences. Female mammals, including humans, usually outlive their male counterparts by a wide margin. In humans, females live on average about 5 per cent longer than males. In African lions and killer whales, the female lifespan is longer by up to 50 per cent.
Predator preferences could also play a part. African lions kill approximately seven times more male than female buffalo, because male buffalo tend to roam alone, whereas females are protected within herds. In contrast, cheetahs kill many more female Thompson’s gazelles than males, presumably because they can outrun female gazelles easier — especially the pregnant ones.
Finally, males and females often suffer differently from parasites and diseases. The COVID-19 pandemic is a striking example of this: the number of infected men and women is similar in most countries, but male patients have higher odds of death compared to female ones.
Sex ratios and sexual selection
Despite our growing knowledge of uneven sex ratios, Darwin’s insight linking sex ratios with sexual selection has received little attention from scientists. The study sought to address this, pulling together these two strands of evolutionary theory in order to revisit Darwin’s argument.
The study looked in particular at the evolution of large males in different species, which are often several times larger than their female counterparts. It is seen in male baboons, elephant seals and migratory birds, for example. Sometimes, females are larger than males — as with some species of bird, such as the African jacana. The scientific term for when one sex in a species is larger than the other is “sexual size dimorphism”.
It’s clear how sexual selection can sometimes create size dimorphism. Knocking out an enemy requires muscular power, while fight endurance requires stamina. So being bigger often means dominating rivals, thereby winning the evolutionary lottery of reproduction. Analysing 462 different species of reptiles, mammals and birds, the study found a tight association between sexual size dimorphism and sex ratios, vindicating Darwin’s conjectures.
But the trend was the opposite to the one Darwin predicted with his limited evidence. It turns out the most intense sexual selection — indicated by larger males relative to females — occurred in species where there were plenty of females for males to choose from, rather than a scarcity of females as Darwin suggested.
Implications for sexual selection
This in no way invalidates Darwin’s theories of natural selection and sexual selection. The finding simply shows that a different mechanism to the one Darwin proposed is driving mating competition for animals living in sex-skewed populations.
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- Lowering Emissions by Accelerating Forest Finance (LEAF) Coalition, a collective of the United States, United Kingdom and Norway governments, came up with a $1 billion fund.
- LEAF is supported by transnational corporations (TNCs) like Unilever plc, Amazon.com, Inc, Nestle, Airbnb, Inc as well as Emergent, a US-based non-profit.
- The world lost more than 10 million hectares of primary tropical forest cover last year, an area roughly the size of Switzerland.
- Ending tropical and subtropical forest loss by 2030 is a crucial part of meeting global climate, biodiversity and sustainable development goals. Protecting tropical forests offers one of the biggest opportunities for climate action in the coming decade.
- Tropical forests are massive carbon sinks and by investing in their protection, public and private players are likely to stock up on their carbon credits.
- The LEAF coalition initiative is a step towards concretising the aims and objectives of the Reducing Emissions from Deforestation and Forest Degradation (REDD+) mechanism.
- REDD+ was created by the United Nations Framework Convention on Climate Change (UNFCCC). It monetised the value of carbon locked up in the tropical forests of most developing countries, thereby propelling these countries to help mitigate climate change.
- It is a unique initiative as it seeks to help developing countries in battling the double-edged sword of development versus ecological commitment.
- The initiative comes at a crucial time. The tropics have lost close to 12.2 million hectares (mha) of tree cover last year according to global estimates released by Global Forest Watch.
- Of this, a loss of 4.2 mha occurred within humid tropical primary forests alone. It should come as no surprise that most of these lost forests were located in the developing countries of Latin America, Africa and South Asia.
- Brazil has fared dismally on the parameter of ‘annual primary forest loss’ among all countries. It has lost 1.7 mha of primary forests that are rich storehouse of carbon. India’s estimated loss in 2020 stands at 20.8 kilo hectares.
- Between 2002-2020, Brazil’s total area of humid primary forest reduced by 7.7 per cent while India’s reduced by 3.4 per cent.
- Although the loss in India is not as drastic as in Brazil, its position is nevertheless precarious. For India, this loss is equivalent to 951 metric tonnes worth carbon dioxide emissions released in the atmosphere.
- It is important to draw comparisons between Brazil and India as both countries have adopted a rather lackadaisical attitude towards deforestation-induced climate change. The Brazilian government hardly did anything to control the massive fires that gutted the Amazon rainforest in 2019.
- It is mostly around May that forest fires peak in India. However, this year India, witnessed massive forest fires in early March in states like Odisha, Uttarakhand, Madhya Pradesh and Mizoram among others.
- The European Union’s Copernicus Atmospheric Monitoring Service claimed that 0.2 metric tonnes of carbon was emitted in the Uttarakhand forest fires.
- Implementation of the LEAF Coalition plan will help pump in fresh rigour among developing countries like India, that are reluctant to recognise the contributions of their forest dwelling populations in mitigating climate change.
- With the deadline for proposal submission fast approaching, India needs to act swiftly on a revised strategy.
- Although India has pledged to carry out its REDD+ commitments, it is impossible to do so without seeking knowledge from its forest dwelling population.
Context:-
At the recently concluded Leaders’ Summit on Climate in April 2021, Lowering Emissions by Accelerating Forest Finance (LEAF) Coalition, a collective of the United States, United Kingdom and Norway governments, came up with a $1 billion fund plan that shall be offered to countries committed to arrest the decline of their tropical forests by 2030.
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Why LEAF Coalition?
Brazil & India
According to the UN-REDD programme, after the energy sector, deforestation accounts for massive carbon emissions — close to 11 per cent — in the atmosphere. Rapid urbanisation and commercialisation of forest produce are the main causes behind rampant deforestation across tropical forests.
Tribes, Forests and Government
Disregarding climate change as a valid excuse for the fires, Indian government officials were quick to lay the blame for deforestation on activities of forest dwellers and even labelled them “mischievous elements” and “unwanted elements”.
Policy makers around the world have emphasised the role of indigenous tribes and local communities in checking deforestation. These communities depend on forests for their survival as well as livelihood. Hence, they understand the need to protect forests. However, by posing legitimate environmental concerns as obstacles to real development, governments of developing countries swiftly avoid protection of forests and rights of forest dwellers.
For instance, the Government of India has not been forthcoming in recognising the socio-economic, civil, political or even cultural rights of forest dwellers. According to data from the Union Ministry of Tribal Affairs in December, 2020 over 55 per cent of this population has still not been granted either individual or community ownership of their lands.
To make matters worse, the government has undertaken systematic and sustained measures to render the landmark Scheduled Tribes and Other Traditional Forest Dwellers (Recognition of Forest Rights) Act, 2006 ineffective in its implementation. The Act had sought to legitimise claims of forest dwellers on occupied forest land.
Various government decisions have seriously undermined the position of indigenous people within India. These include proposing amendments to the obsolete Indian Forest Act, 1927 that give forest officials the power to take away forest dwellers’ rights and to even use firearms with impunity.
There is also the Supreme Court’s order of February, 2019 directing state governments to evict illegal encroachers of forest land or millions of forest dwellers inhabiting forests since generations as a measure to conserve wildlife. Finally, there is the lack of data on novel coronavirus disease (COVID-19) deaths among the forest dwelling population;
Tardy administration, insufficient supervision, apathetic attitude and a lack of political intent defeat the cause of forest dwelling populations in India, thereby directly affecting efforts at arresting deforestation.
Way Forward
Tuntiak Katan, a global indigenous leader from Ecuador and general coordinator of the Global Alliance of Territorial Communities, aptly indicated the next steps at the Climate Summit:
“The first step is recognition of land rights. The second step is the recognition of the contributions of local communities and indigenous communities, meaning the contributions of indigenous peoples.We also need recognition of traditional knowledge practices in order to fight climate change”
Perhaps India can begin by taking the first step.