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Our Expert Voices conversation on why sex exists.

Charles Darwin famously asked why organisms should be produced by combining two sexual elements, instead of by cloning: "The whole subject is as yet hidden in darkness." Evolutionary biologists are still asking this question, but some progress has been made. One idea — with empirical support from studies of New Zealand snails that have sexual and asexual females and lots of virulent parasites — is that sexual reproduction protects populations from disease. That depends on reciprocal evolution between hosts and parasites. The basic idea is that cloning is very good when rare. The clones are all female, and this gives them a massive reproductive advantage. But, once the clone becomes common, it can become the target of rapidly evolving parasites. If these parasites are common and virulent, they could drive the clone back down in frequency, and thus prevent it from replacing the outcrossing females (and males). In contrast, outbred sexual populations can be highly diverse for disease-resistance genes, which reduces the spread of infection among offspring. The bottom line: Sexual reproduction produces genetically variable offspring, which may give sexual females an advantage over asexual females in the face of rapidly evolving parasites. Other voices in the conversation: Sarah Otto, theoretical biologist, University of British Columbia: Sex is evolution's answer to an ever-changing world Joan Roughgarden, evolutionary biologist, University of Hawai'i: Male, female: it goes back to size

Go deeper

Everyone wants to be an influencer

Illustration: Aïda Amer/Axios

The number of people looking to become online influencers has exploded during the pandemic.

Why it matters: Almost anyone can find themselves in a position to become an influencer, and brands are throwing billions of dollars at online content creators.

At least 3 dead after Amtrak train derails in Montana

Photo: Jacob Cordeiro/Twitter

An Amtrak train derailed near Joplin, Montana, resulting in at least three deaths and multiple injuries to passengers and crew on Saturday, per authorities and a company statement.

The big picture: 141 passengers and 16 crew members were estimated to be on the Empire Builder train, traveling from Chicago to Seattle and Portland, when eight of the 10 cars derailed about 4p.m., Amtrak said early Sunday.

Updated 11 hours ago - Politics & Policy

Federal judge blocks vaccine mandate for NYC teachers

Students are dismissed from the first day of school at PS 133 in Brooklyn on Sept. 13. Photo: Michael Nagle/Xinhua via Getty Images

A federal appeals court is set to hear a challenge Wednesday to a vaccine mandate planned for New York City school employees.

Why it matters The vaccine mandate was set to begin on Monday, prompting concerns over staffing shortages in schools across the nation's largest school system. But a judge on Friday temporarily blocked the measure, per AP.

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