D
As PhD research goes, Brian Wisenden might be envied: watching baby fish swimming swiftly through the clear waters in the Costa Rican tropical dry forest. By recording their growth and numbers, he hoped to look at their risks of being eaten. Instead, he witnessed something strange. Many groups were increasing in numbers. In these groups, some were smaller than others, suggesting they weren’t siblings. Wisenden had accidentally discovered that the fish, called convict cichlids, adopt each other’s babies. Why would they do that, he wondered?
In the human world, we think of adoption as a selfless act. But in nature, its presence is puzzling. Taking on the burden of bringing up babies with no genetic link would seem to reduce an animal’s chance of survival or at least provide no gain. Yet, adoption is surprisingly common in the natural world.
Take the eastern grey kangaroo. Between 2008 and 2013, Wisenden followed the fates of 326 baby kangaroos in the Wilsons Promontory National Park in Victoria and recorded 11 cases of pouch (育儿袋) swapping. The circumstances behind some of these adoptions aren’t known, but four were straight swaps and another four occurred after a mother had lost her own baby. How come? Before independence, baby kangaroos go through a period inside and outside their mothers pouch. Following out-of-pouch attempts, mothers normally sniff their young before allowing them back in, but Wisendens team suspect that during an emergency they may omit the sniff test, allowing a weak baby to quickly climb in before fleeing from danger.
Some of nature’s adoptions are, actually, driven by young. In burrower bugs (土蝽), for example, females lay a nest of eggs close to those of unrelated bugs. Mother bugs tend their developing eggs before they hatch, and then feed babies nuts from weedy mint plants. Finding nuts is a competitive business, so not every mother bug gets her fair share. And if the delivery rate isn’t up to standard, clever young may abandon their mothers to join a better-fed group.
The consequences of adoption following mistaken identity can be horrible. The true babies of adopting mothers were abandoned. But it can have remarkable benefits, not just for adoptees but also for adoptive parents.
32. What can we learn about Wisenden’s research about baby fish?
A. It was beyond his expectations.
B. It put many rare species at risk.
C. It showed a genetic similarity in fish.
D. It found a new way to protect forests.
33. What does the underlined word “omit” mean in the passage?
A. confirm. B. repeat.
C. adopt. D. skip.
34. Why would some burrower hugs abandon their mothers?
A. To live in warmer nests. B. To reproduce.
C. To seek for better parenting. D. To adapt to competition earlier.
35. What may the author most probably talk about next?
A. The causes of accidental adoption. B. The processes of accidental adoption.
C. The drawbacks of accidental adoption. D. The advantages of accidental adoption.
