Lemurs have poor eyesight because Madagascar has no poisonous snakes!
http://news.yahoo.com/s/nm/20060720/sc_nm/science_snakes_dc
< Snake-spotting may have helped us evolve -study
Thu Jul 20, 5:03 PM ET
Snakes may make people jump for a good reason -- human close-up vision may have evolved specifically to spot the reptiles, researchers reported on Thursday.
Humans, monkeys and other primates have good color vision, large brains, and use their vision to guide reaching and grasping.
But while some scientists believe these characteristics evolved together as early primates used their hands and eyes to pick fruit and other foods, Lynne Isbell, a professor of anthropology at the University of California Davis, believes they may have evolved to help primates evade snakes.
"A snake is the only predator you really need to see close up. If it's a long way away it's not dangerous," said Isbell, who has published her theory in the Journal of Human Evolution.
Neurological studies show the structure of the brain's visual system seems to be well connected to brain structures involved in vigilance, fear and learning, she said.
Mammals evolved about 100 million years ago and fossils of snakes with mouths big enough to eat those mammals appear at about the same time, she pointed out.
Other predators such as big cats, and hawks and eagles, evolved later. And then venomous snakes evolved about 60 million years ago, which forced primates to get better at detecting them.
"There's an evolutionary arms race between the predators and prey. Primates get better at spotting and avoiding snakes, so the snakes get better at concealment, or more venomous, and the primates respond," Isbell said.
And there are no dangerously venomous snakes on Madagascar, and lemurs, which only live on that large island and which have poor eyesight, have not evolved much in other ways in the past 60 million years, either, Isbell added.
Copyright © 2006 Reuters Limited.
< Snake-spotting may have helped us evolve -study
Thu Jul 20, 5:03 PM ET
Snakes may make people jump for a good reason -- human close-up vision may have evolved specifically to spot the reptiles, researchers reported on Thursday.
Humans, monkeys and other primates have good color vision, large brains, and use their vision to guide reaching and grasping.
But while some scientists believe these characteristics evolved together as early primates used their hands and eyes to pick fruit and other foods, Lynne Isbell, a professor of anthropology at the University of California Davis, believes they may have evolved to help primates evade snakes.
"A snake is the only predator you really need to see close up. If it's a long way away it's not dangerous," said Isbell, who has published her theory in the Journal of Human Evolution.
Neurological studies show the structure of the brain's visual system seems to be well connected to brain structures involved in vigilance, fear and learning, she said.
Mammals evolved about 100 million years ago and fossils of snakes with mouths big enough to eat those mammals appear at about the same time, she pointed out.
Other predators such as big cats, and hawks and eagles, evolved later. And then venomous snakes evolved about 60 million years ago, which forced primates to get better at detecting them.
"There's an evolutionary arms race between the predators and prey. Primates get better at spotting and avoiding snakes, so the snakes get better at concealment, or more venomous, and the primates respond," Isbell said.
And there are no dangerously venomous snakes on Madagascar, and lemurs, which only live on that large island and which have poor eyesight, have not evolved much in other ways in the past 60 million years, either, Isbell added.
Copyright © 2006 Reuters Limited.