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W.-H. Li et al.
1 Introduction
Color vision is a truly multidisciplinary subject involving physics, psychology, neuroscience, ophthalmology, genetics, ecology, evolution, molecular biology, biochemistry, etc. It has intrigued philosophers and scientists since Plato. While past progress
was made mainly from studies in physics, psychology, and vision science, recent
progress has been mainly due to the advent of molecular and biochemical techniques such as gene cloning, DNA sequencing, site-directed mutagenesis, and biochemical assays of pigment proteins. Thanks to new techniques and traditional
means, we now have a much better knowledge of the various genetic systems of
color vision in primates, the origins and evolution of these systems, and the critical
amino acid residues responsible for spectral sensitivity differences among primate
photopigments. We shall review progress in these topics. In addition, we shall
discuss how gene conversion has greatly complicated the inference of the evolutionary history of the systems. Finally, we shall discuss the role of lifestyle
(nocturnality or diurnality) and the role of natural selection in the evolution of
primate color vision systems.
2 Primate Taxonomy
We start with a sketch of the primate phylogeny (Fig. 1; see Goodman et al. 1998).
The primates are traditionally classified into the simians (higher primates) and the
prosimians. The prosimians are divided into two groups: (1) the lemurs, bushbabies,
lorises, etc., and (2) the tarsiers. The tarsiers are actually more closely related to the
simians than to the other prosimians. The simians consist of the New World monkeys (NWMs) and the Old World primates. The latter includes Homo sapiens (humans), the apes, and the Old World monkeys (OWMs). The NWMs are often classified into two families, Cebidae and Atelidae; alternatively, Atelidae is further
divided into two families, Atelidae and Pitheciidae (Schneider et al. 1993, 1996).
3 Color Vision Systems in Primates
3.1 Old World Primates
Among the mammals, the Old World primates possess the most sophisticated color
vision system. They are trichromatic because they possess three types of pigments:
the blue (short wavelength), green (middle wavelength), and red (long wavelength)
pigments (opsins). The blue opsin is encoded by an autosomal gene, while the red
and green opsins are encoded by two tightly linked duplicate genes on the X chromosome (Nat hans et al. 1986a,b). [A normal human may possess up to 5 green
opsin genes, but since they are almost identical and since only the 5' most green
W.-H. Li et al.
1 Introduction
Color vision is a truly multidisciplinary subject involving physics, psychology, neuroscience, ophthalmology, genetics, ecology, evolution, molecular biology, biochemistry, etc. It has intrigued philosophers and scientists since Plato. While past progress
was made mainly from studies in physics, psychology, and vision science, recent
progress has been mainly due to the advent of molecular and biochemical techniques such as gene cloning, DNA sequencing, site-directed mutagenesis, and biochemical assays of pigment proteins. Thanks to new techniques and traditional
means, we now have a much better knowledge of the various genetic systems of
color vision in primates, the origins and evolution of these systems, and the critical
amino acid residues responsible for spectral sensitivity differences among primate
photopigments. We shall review progress in these topics. In addition, we shall
discuss how gene conversion has greatly complicated the inference of the evolutionary history of the systems. Finally, we shall discuss the role of lifestyle
(nocturnality or diurnality) and the role of natural selection in the evolution of
primate color vision systems.
2 Primate Taxonomy
We start with a sketch of the primate phylogeny (Fig. 1; see Goodman et al. 1998).
The primates are traditionally classified into the simians (higher primates) and the
prosimians. The prosimians are divided into two groups: (1) the lemurs, bushbabies,
lorises, etc., and (2) the tarsiers. The tarsiers are actually more closely related to the
simians than to the other prosimians. The simians consist of the New World monkeys (NWMs) and the Old World primates. The latter includes Homo sapiens (humans), the apes, and the Old World monkeys (OWMs). The NWMs are often classified into two families, Cebidae and Atelidae; alternatively, Atelidae is further
divided into two families, Atelidae and Pitheciidae (Schneider et al. 1993, 1996).
3 Color Vision Systems in Primates
3.1 Old World Primates
Among the mammals, the Old World primates possess the most sophisticated color
vision system. They are trichromatic because they possess three types of pigments:
the blue (short wavelength), green (middle wavelength), and red (long wavelength)
pigments (opsins). The blue opsin is encoded by an autosomal gene, while the red
and green opsins are encoded by two tightly linked duplicate genes on the X chromosome (Nat hans et al. 1986a,b). [A normal human may possess up to 5 green
opsin genes, but since they are almost identical and since only the 5' most green