Yet evolution has created an unexpected conflict.
Although each flatworm can technically act as either s3x, neither wants to take on the role of motherhood.
The result is one of the strangest battles in the animal kingdom.
The Hidden Cost of Reproduction
To understand why these conflicts occur, scientists point to a fundamental principle of evolutionary biology: reproduction is expensive.
For females in many species, producing eggs requires enormous amounts of energy and resources.
The costs do not stop there.
After fertilization, the developing embryos require additional nutrients and biological investment.
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