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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[wptelegram-join-channel link=”https://t.me/s/upsctree” text=”Join @upsctree on Telegram”]2021 WEF Global Gender Gap report, which confirmed its 2016 finding of a decline in worldwide progress towards gender parity.
Over 2.8 billion women are legally restricted from having the same choice of jobs as men. As many as 104 countries still have laws preventing women from working in specific jobs, 59 countries have no laws on sexual harassment in the workplace, and it is astonishing that a handful of countries still allow husbands to legally stop their wives from working.
Globally, women’s participation in the labour force is estimated at 63% (as against 94% of men who participate), but India’s is at a dismal 25% or so currently. Most women are in informal and vulnerable employment—domestic help, agriculture, etc—and are always paid less than men.
Recent reports from Assam suggest that women workers in plantations are paid much less than men and never promoted to supervisory roles. The gender wage gap is about 24% globally, and women have lost far more jobs than men during lockdowns.
The problem of gender disparity is compounded by hurdles put up by governments, society and businesses: unequal access to social security schemes, banking services, education, digital services and so on, even as a glass ceiling has kept leadership roles out of women’s reach.
Yes, many governments and businesses had been working on parity before the pandemic struck. But the global gender gap, defined by differences reflected in the social, political, intellectual, cultural and economic attainments or attitudes of men and women, will not narrow in the near future without all major stakeholders working together on a clear agenda—that of economic growth by inclusion.
The WEF report estimates 135 years to close the gap at our current rate of progress based on four pillars: educational attainment, health, economic participation and political empowerment.
India has slipped from rank 112 to 140 in a single year, confirming how hard women were hit by the pandemic. Pakistan and Afghanistan are the only two Asian countries that fared worse.
Here are a few things we must do:
One, frame policies for equal-opportunity employment. Use technology and artificial intelligence to eliminate biases of gender, caste, etc, and select candidates at all levels on merit. Numerous surveys indicate that women in general have a better chance of landing jobs if their gender is not known to recruiters.
Two, foster a culture of gender sensitivity. Take a review of current policies and move from gender-neutral to gender-sensitive. Encourage and insist on diversity and inclusion at all levels, and promote more women internally to leadership roles. Demolish silos to let women grab potential opportunities in hitherto male-dominant roles. Work-from-home has taught us how efficiently women can manage flex-timings and productivity.
Three, deploy corporate social responsibility (CSR) funds for the education and skilling of women and girls at the bottom of the pyramid. CSR allocations to toilet building, the PM-Cares fund and firms’ own trusts could be re-channelled for this.
Four, get more women into research and development (R&D) roles. A study of over 4,000 companies found that more women in R&D jobs resulted in radical innovation. It appears women score far higher than men in championing change. If you seek growth from affordable products and services for low-income groups, women often have the best ideas.
Five, break barriers to allow progress. Cultural and structural issues must be fixed. Unconscious biases and discrimination are rampant even in highly-esteemed organizations. Establish fair and transparent human resource policies.
Six, get involved in local communities to engage them. As Michael Porter said, it is not possible for businesses to sustain long-term shareholder value without ensuring the welfare of the communities they exist in. It is in the best interest of enterprises to engage with local communities to understand and work towards lowering cultural and other barriers in society. It will also help connect with potential customers, employees and special interest groups driving the gender-equity agenda and achieve better diversity.